Wood, Bark, and Stem Anatomy of Gnetales: a Summary

WOOD, BARK, AND STEM ANATOMY OF GNETALES: A SUMMARY

SHERWIN CARLQUIST

Santa Barbara Botanic Garden, 1212 Mission Canyon Road, Santa Barbara, California 93105

Data from a series of eight papers, representing a survey of Gnetales at the species level, are summarized in order to develop concepts on the relationship between the anatomical data and ecology, phylogeny. and systematics. Most of the characters and character states newly reported have phylogenetic and ecological correlations for Gnetales as a whole rather than systematic significance within the genera. Wood features are sensitively related to habit, although strategies in lianoid species of Ephedra differ from those in lianoid Gnetuin species. Data also bear close relationships to organography. Vessel details are given special attention because workers have questioned whether vessels originated in Gnetales independently of those in angiosperms. and thus whether or not vessel origin in the two groups is a synapomorphy. The evidence cited here favors origin of vessels in Gnetales independent of vessel origins in angio sperms. Hitherto unappreciated contrasts between vessels of Gnetales and those of angiosperms are detailed: the torus margo structure of pits in Gnetales (both Ephedra and Gnetuin), and the aspiration ability of gnetalean pits represent modes of conduction and promotion of conductive safety different from those in angiosperms, and the shape difference (circular vs. scalariform), cited in data matrices of cladograms. is secondary to the different functional syndromes. The intercalation of circular bordered pits into helical secondary wall thickenings of primary xylem tracheary elements of Ephedra and Gneturn (a feature found also in conifers and Ginkgo but not in angiosperms) is given new functional interpretations. Ephedra and Gnetum contain both tracheids and fiber-tracheids that co-occur in a mode different from that in angiosperms which Contain both cell types together. Ray structure like that of Gnetales occurs widely within seed plants and likely offers little conclusive information about relationships. Wood data on Gnelalec are compatible with the hypothesis that a vesselless group of gymnosperms, such as Pentoxylales or Bennettitales, is the closest sister group of angiosperms. Formation of successive cambia in Gnetum differs from that in Welwirschia: the latter has phellem but no other bark. Because Welwiischia has only phellem, there are more numerous bark features in common between Ephedra and Gnetum than one might have expected. The three genera appear monophyletic on the basis of wood and bark. Infrageneric anatomical features of systematic importance are few, although the arboreal Gnetum gneinon differs from the lianoid Gnetuni species in significant ways.

Introduction dence: the new wood and bark information must be analyzed and summarized in diverse contexts. This article summarizes eight papers that attempt to The studies on wood and bark of Gnetales at the survey wood, bark, and stem anatomy of Gnetales at species level was begun with a study of the New the species level, and thereby concludes the series. World species of Ephedra (Carlquist 1989), the Old With respect to anatomy of wood and bark, earlier lit World species of Ephedra (Cariquist 1992), and the erature (e.g., Martens 1971) is based on study of a very phenomenon of near-vessellessness in some high-al small number of species. Therefore, a new survey, rep pine species of Ephedra (Carlquist 1988b). The initi resenting many more species than had been studied ation of the survey with study of the New World spe before, was initiated. This point is made because ear cies of Ephedra was related to the fact that material lier conclusions about the nature of wood and bark of of those species was more readily available to me. Al Gnetales are based on a small base of information, and though Welwitschia has been studied for many de many character states summarized here do not appear; cades, important new structural data proved worthy of therefore, in recent papers on relationships of Gnetales. reporting (Carlquist and Gowans 1995). One tree spe The fact that much new information has been acquired cies of Gnetum, Gnetum gnemon, is widespread requires integration of that information in various (Markgraf 1930) and was considered in a separate pa ways: (1) simple descriptions of features, (2) alterna per (Carlquist 1994) because this species differed so lions of earlier descriptions, (3) integration of the new much from the lianoid species of the genus. Both Af information into the patterns provided by earlier work rican lianoid species of Gnetum were available (Carl ers, (4) analysis of the phylogenetic significance of the quist and Robinson 1995); all New World species ex data now available, and (5) consideration of the eco cept a recently named one were studied (Cariquist logical implications of wood and bark data. The task 1996b). The series concluded with a study of Indoma at hand in analyzing these data sets, therefore, is much lesian and Asiatic lianoid species (Carlquist I 996a). more than citation of how features of wood impinge Representation at the species level was 92% in Ephed on hypotheses of seed plant evolution. The organiza ra and 66% in Gnetum. Although less than optimal in tion of this article cannot, therefore, be a linear ex coverage of the Indomalesian and Asiatic species of amination of past hypotheses in terms of current evi Gnetum, the survey provides a baseline to which in formation on species not included can readily be added Address for correspondence and reprints: 4539 Via Huerto, Santa as material becomes available. Barbara, California 93110. Previous studies on wood, bark, and axis anatomy Manuscript received October 1995; revised manuscript received of Ephedra, Gnetum, and Welwitschia were summa February 1996. rized by Pearson (1929) and Martens (1971). The de

S58 CARLQUIST—ANATOMY OF GNETALES S59 scription of G. gnernon wood by Greguss (1955) has (“anomalous secondary growth”) in the two genera not been cited widely. Information on wood anatomy cannot be regarded as a synapomorphy but rather as was assembled on a floristic basis for Ephedra by Fahn two autapomorphies. On the contrary, the presence of et al. (1985) and for Gnetum by ter Welle and Detienne minute intercellular calcium oxalate crystals in Ephed (1991). Muhammad and Sattler (1982) presented some ra and Welwitschia (a feature otherwise not reported observations on certain Gneturn vessels as a way of in vascular plants, to my knowledge), seems best in promoting particular phylogenetic concepts. terpreted as a symplesiomorphy. Perhaps phyletically By surveying Gnetales at the species level, much the most important new report is that of tori in pits of new information was uncovered. The following fea tracheary elements of Gneturn, because this feature tures were newly reported for Gnetales as a whole: (1) represents a clearly gymnospermous feature rather helical thickenings in secondary xylem vessels and tra than one transitional to angiosperms. These examples cheids of Ephedra (Carlquist 1989, 1992); (2) near show that the new reports of structural features in Gne vessellessness in Ephedra (Carlquist 1988b); (3) pres tales take on significance when integrated with our ence and nature of fiber-tracheids as well as tracheids previous knowledge of wood, bark, and stems of Gne in wood, and distribution of these cell types with re tales. Thus, before conclusions with regard to ecology lation to each other, in Ephedra (Carlquist 1989, 1992) and phylogeny are attempted below, a summary at the and Gnetum (Carlquist 1994, 1996a, 1996b); (4) pres generic level of axial anatomy is presented. Infrage ence and nature of axial parenchyma in Ephedra (Carl neric diversity is cited in terms of exceptions to com quist 1989, 1992), Gneturn (Cariquist 1994, 1996a, mon conditions within the genera. Although the salient 1996b; Cariquist and Robinson 1995), and features of wood and bark of Gnetales are summarized Welwitschia (Cariquist and Gowans 1995); (5) diver below, many details presented in the earlier papers of sity in axial parenchyma distribution types in Ephedra this series are not repeated here. Likewise, details on (Carlquist 1989, 1992) and Gnetum (Carlquist 1994, methods, techniques, material, and terminology are not l996a, 1996b; Carlquist and Robinson 1995); (6) mi repeated here. nute calcium oxalate crystals lining intercellular spaces in Ephedra (Carlquist 1989, 1992) and Welwitschia Wood anatomy (Carlquist and Gowans 1995); (7) tyloses in vessels of EPHEDRA Gnetum (Carlquist 1996b); (8) tyloses in laticifers of Gnetum (Cariquist 1996b); (9) storied structure of Stems and roots of Ephedra feature a single cam wood in Ephedra (Cariquist 1989, 1992); (10) phel bium with secondary phloem formed externally and loderm origin of lateral menstem activity in Weiwit secondary xylem, internally. Rays, chiefly multiseriate, schia (Carlquist and Gowans 1995); and (11) presence separate broad fascicular areas. Particular fascicular ar of various types of sclerenchyma and crystals in bark eas may experience addition of secondary xylem more of Ephedra (Carlquist 1989, 1992) and Gneturn (Carl rapidly than others; this lack of synchronization be quist 1994, 1996a, 1996b; Carlquist and Robinson comes evident in diagonal orientation of ray cells that 1995). interconnect equivalent portions of adjacent fascicular In addition, some features were newly reported for areas (Cariquist 1989, figs. 8, 12; Carlquist 1992, figs. particular genera of Gnetales, although they were al 36—38; Lev-Yadun and Aloni 1993, figs. 3, 4). In rath ready reported for one or both genera not listed: (1) er old Ephedra stems (diameter depends on species) tori in pits of tracheary elements in Gneturn (Carlquist distortion in orientation of fascicular and ray portions 1996a, l996b; Carlquist and Robinson 1995); (2) can occur (Lev-Yadun and Aloni 1993). This phenom wood plan as in other plants with secondary growth, enon should not be equated with lateral meristem ac rather than vascular strands organized on some other tivity leading to the production of successive cambia, basis, in Welwitschia (Carlquist and Gowans 1995); features characteristic of Gnetum and Welwitschia. (3) growth rings in Gnetum (Carlquist 1994); (4) pres Vessels of Ephedra are essentially solitary; if con ence of uniseriate as well as multiseriate rays in tacts between vessels occur, they appear attributable to Ephedra (Carlquist 1989, 1992); (5) branching in la random vessel placement in wood in which vessel den ticifers in Gneturn (Carlquist 1996b); (6) secretory ca sity is great. There is no tendency toward vessel group nals, in addition to laticifers, in Gneturn (Cariquist ing as there is in dicotyledons that have fiber-tracheids 1 996a); and (7) nature of phloem parenchyma, with or libriform fibers as the imperforate tracheary element respect to secondary xylem cells, in Gneturn (Cariquist type (Carlquist 1 984a). Ephedra, like other Gnetales, 1 996a). exemplifies the hypothesis that when tracheids are Some of these features are of major importance phy present as the imperforate tracheary element type, logenetically. For example, the demonstration that lat grouping of vessels does not occur to any appreciable eral meristem activity originates from cortex in Gne extent (Cariquist 1984a). The shrubby species of turn (La Rivière 1916; Carlquist 1994, 1996a, 1996b; Ephedra show strongly marked growth rings. Not only Carlquist and Robinson 1995) but from phelloderm in are vessels larger in earlywood than in latewood but Welwitschia (Carlquist and Gowans 1995) means that vessels may be absent in latewood in some species lateral meristems have had different origins in the two (Carlquist 1989, 1992). In a few species from high genera and that the presence of successive cambia elevations, vessels are extremely few in number, re /

SDN3IDS LNV’Id 1O ‘1VNf1Of ‘IVNOLLVNJ3LNI 09S CARLQUIST—ANATOMY OF GNETALES S6 I

suiting in a near-vesselless condition (Cariquist latter illustrated in Carlquist 1992, fig. 24); occasional 1988b). The lack of vessels in iatewood in dicotyle large fiber-tracheid aggregations are present. dons that have tracheids as an imperforate tracheary Rays are mostly multiseriate, but uniseriates occur element type has been interpreted as representing max in a few species, in which they are much less common imal abundance of tracheids, which are more resistant than multiseriates. Rays are composed of upright, to formation of air embolisms than are vessel elements square, and procumbent cells; upright cells predomi (Cariquist 1988a). Woods are mostly ring porous. nate in rays of smaller-diameter samples, whereas pro The vessel elements of Ephedra have perforation cumbent cells increase in abundance as a stem increas plates composed of foraminate (circular) perforations es in diameter (Cariquist 1989). Starch grains are similar to the outlines of pit cavities of lateral wall pits common in ray cells, as they are also in fiber-tracheids. on vessels on tracheid-to-vessel or tracheid-to-tracheid Minute calcium oxalate crystals occur among tra pits (figs. 1—4). There is little variation in these fora cheary elements and ray cells. Although uncommon in minate perforations (sometimes termed “ephedroid a few species of Ephedra, these minute crystals are perforations”). The number of series of perforations abundant in the vast majority of Ephedra woods. ranges from one, in the most slender vessels, to two Storying has been reported in Ephedra coryi Reed (fig. 1) or three (figs. 2—4), but rarely more than three, var. viscida Cutler (Carlquist 1989), Ephedra equise series. There are borders on perforations in some spe tina Bunge, and E. foliata (Carlquist 1992). Storying cies (fig. 1), but most borders are minimal (figs. 2—4). is more common in dicotyledons with short fusiform Both prominently bordered and minimally bordered cambial initials, so the occurrence of storying in perforations can characterize a single species (figs. 1, Ephedra, which has shorter fusiform cambial initials 2), although perforations tend to be more prominently than do other gymnosperms (with the exception of bordered in Ephedra americana Humb. & Bonpi. and Welwitschia), is not surprising (Cariquist 1992). Ephedra andina Poepp. ex Mey. (Carlquist 1989). No Wood of lianoid or scandent species of Ephedra has fusion of perforations is evident, although in a few some distinctive features. Lianoid species include species, such as Ephedra kokanica Regel, relatively Ephedra pedunculata Engelmann ex Watson in the large perforations placed closely tend to be somewhat New World, and in the Old World, species of section polygonal in outline rather than circular (fig. 4). Pits Pseudobaccatae, tribe Scandentes: Ephedra altissima on lateral walls of vessels, like tracheid-to-tracheid Desf., Ephedra aphylla Forssk., Ephedra campylopoda pits, are circular and fully bordered, and have promi C. A. Mey., E. foliata, Ephedra fragilis Desf., and E. nent tori connected to margo threads (fig. 9). Helical kokanica. Compared to nonlianoid species, these spe thickenings occur in inner surfaces of secondary xy cies have a much greater density of vessels per mm2 lem vessels of the majority of New World species of transection, longer vessel elements, and greater per (Cariquist 1989) and some Old World species (Carl foration diameter (table 1), as well as less thick walls quist 1992); in species with helical sculpturing in ves on imperforate tracheary elements. Differences be sels, such sculpturing also occurs in tracheids. lrnper tween lianoid and nonlianoid Ephedra species with re forate tracheary elements in Ephedra are clearly spect to vessel diameter and in wall thickness of ves differentiated into tracheids, with large bordered pits sels are negligible. and without cellular contents, and fiber-tracheids, which have pits bordered on contacts with vessels or WELwITscHIA tracheids, but pits simple or quite vestigially bordered The axis of Welwitschia consists of a long taproot on contacts with other fiber-tracheids. Fiber-tracheids and a relatively short, wide stem. From investigations of Ephedra are nucleate but not septate. The reason to date, there is every reason to believe that the same why fiber-tracheids of Ephedra are not termed “axial histology (except for organization of primary xylem) parenchyma” is that they are not strands of cells sep is found in both roots and stems. The vascular strands arated by lignified walls; such strands do occur in a of stems are so contorted that secondary growth and few species of Ephedra (Ephedra foliata Boiss., E. histology in them cannot be readily demonstrated. kokanica Regel; Carlquist 1992, fig. 31). By contrast, Therefore, descriptions here are based primarily upon Gnetum characteristically has both fiber-tracheids and root material. In both stems and roots, there is a first axial parenchyma. Other arguments for use of this ter cambium that produces a limited amount of secondary minology, not used throughout Gnetales prior to the xylem and secondary phloem, not unlike the second current series of papers, have been presented (Carl ary growth in seedlings of various vascular plants with quist 1989, p. 421). Fiber-tracheids in Ephedra are ar secondary growth. This stage has been illustrated by ranged in diffuse or diffuse-in-aggregates fashion (the Bower (1881), Sykes (1910), Pearson (1929), and But-

Figs. 1—4 SEM photographs of perforation plates of Ephedra, from radial sections. Figs. 1, 2, Ephedra major Host, Stainton 18280. Fig. 1, Perforation plate with clearly bordered perforations. Fig. 2, Perforation plates with minimal borders. Fig. 3, Ephedra intermedia Schrenk, Elias. July 21, 1983; perforations of nearly circular outline, minimally bordered. Fig. 4, E. kokanica, Elias 9742; relatively large perforations somewhat polygonal in outline. Bars at upper left in each photomicrograph = 10 m.

Se- to

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perforations foraminate of merging that grooves have tracheids and elements Vessel data).

and

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suggest sizes and shapes perforation (original as tracheids numerous as 30%—35% are only

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foraminate-coalescent; as characterized be can 7), elements vessel The wide. elements tracheary three to

5—

(figs.

here

illustrated those as such vessels, wider one are which xylem, fascicular of bands the of some

somewhat

in plates

15). Perforation fig. 1994, quist interrupts parenchyma Axial cells. ray some among es

(Carl

perforations

well-bordered of of row a consist spac intercellular line crystals oxalate calcium Minute

that

plates

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have vessels of these rowest upright. are cells ray All multiseriate. to idly widen

nar The

5—7). (figs.

occasionally occur plates foration rap but uniseriate as begin rays Some 1995). Gowans

per

foraminate

xylem, primary near vessels narrow and (Carlquist present are areas ray and fascicular lem:

shown).

portion 8,

(fig. simple predominantly are xy secondary with plants vascular of other that like

plates

1994). Perforation (Carlquist collections few a much plan xylem secondary a has above, strand” cular

observed been

sort have inconspicuous an of rings “vas term the vague of use the despite xylem, ondary

Growth

dictate.

would vessels of placement random sec the Nevertheless, 1995). Gowans and (Cariquist

what

likely number 1.09—a group, per vessels produce cambia the xylem secondary the with pared

number

so—mean or nearly solitary are Vessels com fibers, phloem gelatinous of abundance by cated

investigation. further of need as indi phloem, secondary of amounts large atively

in a

topic This

is cylinder. main of the phloem and rel produce Welwitschia of cambia successive The

xylem

with interconnected be must cambia these from quist 1989).

formed tissue new vascular the way some in although (Carl Ephedra of those like much 1995) Gowans and

1994),

(Carlquist in bark formed from cambia inate (Carlquist crystals oxalate calcium minute with lined

orig segments

These Keng 1975). (Rao and be found are tissue conjunctive the in spaces intercellular Many

may

segments xylem additional trees, of older bases crystals. oxalate calcium large relatively embedded

in age;

moderate of trees in least at cylinder woody are of which surface outer the near walls latinous

single

and cambium a single has gnemon Gnetum ge with fibrosciereids large and cavities, secretory ma,

parenchy of starchy consist tissues

Conjunctive sue.”

GNEMON GNETuM

tis “conjunctive termed are strands, vascular the in

served. formed cells parenchyma than other meristem, lateral

were fiber-tracheids no present; elements cheary the by produced tissues of parenchyma the All 1995).

tra

imperforate of type the only are Tracheids tori. of Gowans and (Carlquist Gnetum of species lianoid of

evidence no with view, sectional in flat are that branes roots and stems in meristems lateral in involved chyma

mem

only

revealed far thus has SEM and microscopy paren of files the radial of that from different origin

light

both with examination Careful (1971). Martens of a mode have thus and phelloderm, with continuous

copied were figures these view; in sectional tical inter- files are radial These meristem. lateral a from

ellip

membranes pit suggest (1960) by Bierhorst ures formed parenchyma files of radial within originate

fig

although elements, tracheary pits of in are absent cambia Subsequent long. before exhausted are bia

Tori 1960).

(Bierhorst perforations circular bordered cam these of origin for sites parenchyma cortical ma,

two,

one, rarely of consist elements of vessel plates parenchy cortical in arise cylinder original the of side

Perforation

Welwitschia. in thickenings shows (1910) out cambia first the Although 1971). (Martens cambia

Sykes

although Ephedra, in as thickenings, than rather successive from formed is cylinder first the of outside

1995)

Gowans 1960; and Carlquist (Bierhorst ities tissue vascular that agree authors all although ured,

cav pit elliptical inner of

extensions lateral represent fig less been have stages Subsequent (1973). al. et ler

species. Indomalesian include species Gnetum Asiatic

original.

Welwitschia on Data rim.

tracheids. of thickness wall mean 7, TWT tim; = tracheids,

length

mean TL 6, mm’; mm 2 transection, per

= area conductive mean 5, CA tm; thickness, =

wall

vessel mean 4, VW tm; elements,

= vessel of length mean 3, VL transection; mm 2 per =

of vessels

number mean VM 2, tm; of vessels,

diameter lumen mean VD 1, columns: to Key =

(1995). and Robinson and Carlquist l996b); 1994, l996a, (1992, Carlquist from Data Sources.

3.6

.21 1364 5.1 1123 20 124 averaged lianas all Gnetum,

3.5 1532 .27 4.6 1250 19 134 lianas Asiatic Gnetum,

4.4 1360 .19 5.7 1057 10 155 lianas World New Gnetum,

2.9 1200 .16 4.9 1062 31 82 lianas African Gnetum,

4.8 1691 .11 3.5 1235 21 82 shrubs) (trees, gnemon Gnetum

3.8

592 .04 5.0 508 249 15 Welwjtschja

2.2 808 .16 2.4 723 143 38 lianoid World Old Ephedra,

3.1

669 .05 2.1 585 65 32 nonlianoid World Old Ephedra,

(7) (6) (5) (4) (3) (2) (1) Group

TW TL CA VW VL VM VD

GNETALE5 OF CHARACTERISTICS WOOD

1 Table

SCIENCES PLANT OF JOURNAL INTERNATIONAL S62 CARLQUIST—ANATOMY OF GNETALES S63 lective pressure for greater conductive area within the and secondary xylem they yield are most clearly vis perforation plate. ible in Gnetum africanum Welw. (Carlquist and Rob Lateral wall pits of vessels have circular bordered inson 1995). pits with a cavity diameter much smaller than the di Cambial action is sluggish in future ray areas but ameter of perforations. These pits bear vestures (fig. much more active in fascicular zones. Wide multise 8) that occur at or near the mouth of the pit aperture, nate rays originate from the successive cambia. Within and vesturing is lacking within the pit cavity. Imper the fascicular areas, biseriate or uniseriate rays also forate tracheary elements consist of both fiber-trache originate (fig. 16). The interrelationships between ids and tracheids. The fiber-tracheids are relatively thin these narrower rays, tracheids, and fiber-tracheids in walled and usually septate; they have vestigially but the lianoid species have not been stated clearly in ear clearly bordered pits that are relatively small and are lier literature. An attempt to clarify this situation can distributed randomly with respect to tracheids (fig. 13). be found in Carlquist (1996a). The vessel elements of Tracheids have thicker walls than fiber-tracheids, lack the lianoid species of Gnetum are much like those of contents and septa, and have large circular bordered G. gnemon; as in that species, only a few narrower pits very close in cavity diameter to those on lateral vessels have foraminate perforation plates, and the ma walls of vessels. No tori have thus far been observed jority of perforation plates are simple. Vesturing is var on pit membranes of G. gnemon tracheary elements. iously represented on lateral wall pits of vessels, but Paratracheal axial parenchyma is vasicentric and rel in no species is vesturing wholly absent in these pits. atively abundant in G. gnemon; apotracheal parenchy In addition to vessel elements, the fascicular sec ma is scarce and is diffuse. Strands consist of four to ondary xylem of lianoid Gnetum species consists of 10 cells, have thin but lignified walls, and contain tracheids, fiber-tracheids, and axial parenchyma (figs. starch and sometimes calcium oxalate crystals (fig. 14, 15). The features by which these three cell types 13). differ from each other are as in G. gnemon, except that Rays are both uniseriate and multiseriate, with al diffuse and diffuse-in-aggregates axial parenchyma are most all cells procumbent, except at tips of multiseriate more abundant than in G. gnemon. The large circular rays and in uniseriate rays. The ray cells have lignified bordered pits of vessel elements and of tracheids have walls. Bordered pits are common on tangential walls pit membranes that bear tori, in at least some species. of ray cells; simple pits predominate elsewhere on ray Tori were observed in G. africanum, Gnetum buch cells. Calcium oxalate crystals of various sizes and hoizianum Engler (Carlquist and Robinson 1995), starch grains are common within ray cells. Gnetum leyboldii Tul. (Carlquist 1996b), Gnetum cus pidatum Blume, and Gnetum microcarpum Blume LIAN0ID SPECIES OF GNETuM (Carlquist 1996a). Liquid-preserved material of all of The lianoid Gnetum species have a first cambium these species was available. Lack of tori might bear a that forms a cylinder of secondary xylem—with a pith relationship to the mode of sample preservation. Tori in the stem, without a pith in the root. Subsequent were demonstrated by both light microscopy and SEM, vascular cylinders arise from successive cambia, and although in some SEM photomicrographs, differenti parenchyma between these vascular cylinders is ation between torus and margo is less marked than in termed “conjunctive tissue” here. Conjunctive tissue Ephedra or conifers. is composed of parenchyma that contains starch and, Radially oriented files of parenchyma cells in sec near rays, calcium oxalate crystals. The conjunctive ondary phloem of lianoid species of Gnetum (fig. 16) tissue may contain laticifers (fig. 17) in some species. have been likened to companion cells (Maheshwari Secretory cavities were observed in conjunctive tissue and Vasil 1961), but they are not sister cells to sieve external to strands of phloem in Gnetum gnemonoides cells and were accurately designated as parenchyma Brongn. The second and perhaps several more of the cells by Esau (1969). What has not been clarified is successive cambia originate in cortical parenchyma. the relationship between these parenchyma cell files Cortical parenchyma would be used up in the forma and the extensions of these files into the secondary tion of these cambia eventually, but what I am terming xylem (fig. 16, bottom). The radial orientation of xy a lateral meristem here forms additional parenchyma lem cells intercontinuous with the phloem parenchyma in the cortical region through production of radial files files suggests that they might be xylem rays, and in of cells (figs. 17, 18). Pearson (1929) hypothesized fact some of them are rays, as confirmed by presence that more than one site of origin for lateral meristem of uniseriate and biseriate rays as seen in tangential activity might occur. However, a cortical site of origin and radial sections of these fascicular zones. However, for origin of lateral meristem activity was demonstrat study of these tangential and radial sections reveals ed in Gnetum by La Rivière (1916), and this has been relatively few such rays, too few to account for the confirmed in each of three main taxonomic and geo numerous radial files of narrow cells in secondary xy graphical groupings of lianoid Gnetum species (Carl lem as seen in transections (fig. 16). The radially ori quist and Robinson 1995; Cariquist 1996a, 1996b). ented rows of cells that lie between radial files of tra Cambia originate within the radial files formed by per cheids prove mostly to be fiber-tracheids or possibly a iclinal divisions I am terming “lateral meristem.” The few axial parenchyma strands. Although fiber-trache origin of these cambia and the first secondary phloem ids were not mentioned for African species of Gnetum 9 L -‘ I

•/ a

4 I1 I 4r 1 I i d i

I IL

S3DNI3S INV’Id dO ‘1VNIflOf 1VNOI1VNLLNI 179S CARLQUIST—ANATOMY OF GNETALES S65

(Carlquist and Robinson 1995), careful study of slides The roster of features in the bark of Gnetum—es of those species revealed fiber-tracheids, albeit in small pecially the diffuse gelatinous fibers and the presence numbers. Therefore, all of the lianoid species of Gne of sclerenchymatous phelloderm—is remarkably sim turn, as well as G. gnernon, are now claimed to possess ilar to that for Ephedra. At least some of these features fiber-tracheids as defined for Gnetum by Cariquist seem likely to be symplesiomorphies. Rather than con (1994). cluding that the similarities between the two genera Bark mark them as more closely related to each other than either is to Welwitschia, one should consider the pos Bark of Ephedra (Cariquist 1989, 1992) has been sibility that in its anatomical structures, as well as in shown contain to the following cell types: (1) sieve its bizarre gross morphology, Welwitschia has departed cells, phloem parenchyma, phloem ray parenchyma from a hypothetical common ancestor and thereby (obliterated to various extents depending on age of contains a number of autapomorphies the other two bark); (2) sclereids derived from axial parenchyma genera lack. cells; (3) suberized phellem; (4) phelloderm (thin walled or sometimes scierenchymatous), often Condusions on organography, habit, and ecology associated with minute intercellular calcium oxalate crystals; (5) sclereids derived from phloem ray cells; ORGAN0GRAPHY (6) gelatinous phloem fibers; in addition, younger In Ephedra, relationships of vessel features to or stems reveal the presence of (7) gelatinous fibers dif ganography were detailed (Carlquist 1989, 447) be fusely distributed in the cortex (fig. 20). The diffuse p. cause collections of particular portions were made in cortical fibers were not mentioned in earlier accounts the field. These data, in sum, show that vessels are of bark because they were not evident once the cortex wider in roots and underground stems than in upright was lost. The diffuse fibers are noteworthy because aerial stems, thereby agreeing with those in dicotyle similar fibers occur in cortex and bark of lianoid Gne dons (Patel 1965). However, the reverse trends occur turn species. Not all of the above seven features may in Gneturn, admittedly on the basis of a small sampling be present in all Ephedra species, and accurate data of lianoid species (Carlquist 1 996a). Vessel diameter on systematic distribution of the features within the in roots is less than it is in genus are not available. stems not only in lianoid Gneturn species but in Gneturn gnernon as well (Carl In Gnetum gnernon bark, the following cell types quist 1994), perhaps because the roots studied occur (Carlquist 1994): (1) thin-walled (nonscleren are smaller than stems (although not dramatically so; see chymatous) phellem; (2) starch-rich parenchyma; (3) data in Cariquist 1994). In dicotyledons, vessels ordi nests of brachysclereids, some of which contain large narily increase in diameter with increase in stem di calcium oxalate crystals; and (4) gelatinous phloem ameter (Cariquist l984b). Increase in vessel diameter fibers. In the lianoid Gneturn species, all of these cell with increase in stem diameter was evident in types occur, but in addition, one may find (5) occa Ephedra (Ephedra boelckii Roig, Ephedra trifurca Torr., sional sciereids in phloem (Cariquist 1996b); (6) ge and Ephedra viridis Coville). Relationships between latinous fibers scattered in the cortex (fig. 19); (7) a quan titative vessel features and cylinder of brachysclereids, outside of the parenchy organography deserve de tailed further study in Gnetum. matous inner cortex but inside of the nests of bra chysciereids (fig. 17, top; fig. 18, top); laticifers (8) HABIT (easily visible in some species, such as Gneturn schwackeanurn Taub. (fig. 17); and (9) sclerenchyma In Ephedra, habit ranges from small shrubs to large tous phelloderm (Carlquist 1 996a). The sclerenchy shrubs to small trees and to lianas or sprawling shrubs. matous cylinder and sclerenchymatous phelloderm are To be sure, the lianas and sprawling species of Ephed absent in underground roots and stems of lianoid spe ra are not a uniform group with respect to habit. The cies (fig. 19; Cariquist 1996a). lianas in Gneturn vary somewhat but seem amply dis There is no bark in the ordinary sense in Weiwit tinct in habit from the tree species Gnetum gnemon schia, only phellem, which contains a few of the giant and Gneturn costaturn K. Schum., judging from the gelatinous fibrosciereids in the walls of which large descriptions of Markgraf (1930). However, Markgraf crystals are embedded. Secondary phloem in Welwit (1930, p. 436) claims that the species one usually sees schia vascular strands does contain large numbers of as a tree, G. gnernon, can be a shrub or a liana as well. the gelatinous phloem fibers of the sort seen in Ephed The nature of lianoid individuals of G. gnernon is in ra and Gneturn bark, however. need of investigation, because such lianas have not

Figs. 5—8 Perforation plates of Gnetum gnenson, Cariquist 8088; from radial sections (figs. 5, 6, 8) illustrated with SEM and from a maceration (fig. 7) illustrated with light microscopy. Fig. 5, Perforation plate showing little alteration from a foraminate condition. Fig. 6, Perforation plate with fewer, larger perforations. Fig. 7, Perforation plate with three perforations, one partially traversed by wall material. Fig. 8, Simple perforation plate (vesturing visible in apertures of lateral wall pits of vessels). Fig. 7, Magnification scale above photograph (divisions = 10 p.m). Figs. 5, 6, 8, Bars, upper left, = 10 aim.

quanti the

Nevertheless,

inapplicable. is used usually This is species. lianoid the in lower much is plate tion

methods

scanning random the by areas comparable perfora bars per of number the species, broad-leaved

finding that

tissue

conjunctive of areas large such in lianoid and both shrubby/arboreal have that plates tion

scattered

and small so

are of xylem areas transectional perfora scalariform with families dicotyledonous in

because

estimate,

an essentially is 2) col. mm 2 , sels per that is observation the Gnetum in plate perforation the

ves of

number (mean density vessel figure for The 1. of simplification to relates habit lianoid the that tion

table

Welwitschia for data the to develop selected interpreta the Reinforcing plate. perforation aminate

was

transection root

typical a differ, undoubtedly tions for the of morphology the of modification for pressure

collec Although

xerophytes. other of various or any selective is no there and lianas, in rates flow increased

succulent,

stem

shrub, desert a of that to comparable accommodate to suffice diameter perforation mean er

not really is

Welwitschia of wood the because ficult, larg slightly a and density vessel greater that siderably

dif

data these of significance the Analyzing schia. con so transpiration reduces microphylly that likely

of Weiwit

xylem secondary for presented been erto very is it Ephedra, In liana. broad-leaved in a and

not hith

data have tracheid and vessel Quantitative tree broad-leaved in a both great is plates perforation

simple for pressure selective the

Evidently, collections. XER0M0RPHY

Gneturn lianoid or arboreal the in either 1.0 above tion

Gneturn. in trend the of esting confirmation a frac only thus is plate perforation per perforations

an inter (3.1 jim), species shrubby the of than those of number mean The simple. are majority far the by

jim) (2.2 are thinner col. 1, 7) (table species Ephedra are foraminate; Gneturn of root or stem any in plates

lianoid the in walls Tracheid be desirable. would perforation few a only whereas foraminate, ways

and dicotyledons in collected infrequently are point are al Ephedra of plates Perforation Ephedra. in than

on this liana. Data related a in than tree a in strength dramatic more are much features vessel quantitative

mechanical promote to wall thickness for lection in differences of papers), series present the in studied

se greater there is that concept the with be accord in collections Gneturn all on based figures 1; (table cies

would This 7. 1, column table in shown as (4.8 jim), spe Gneturn to nonlianoid lianoid comparing When

collections G. the gnernon do than jim) (3.6 walls ner 1975). (Carlquist dons

have thin Gnetum of species lianoid the in Tracheids dicotyle in species xeric

characterize elements vessel

181). 1975, (Cariquist vessels thicker-walled have shorter since xeromorphic, more are species shrubby

to of dicotyledons species lianoid for tendency the if expected be trend would This significant. tistically

with accord is too, in This, 1, 4). col. G. gnernon (table also sta 3) is 1, col. (table species World Old lianoid

in than lianas Gnetum the in thicker are appreciably non versus lianoid in elements of vessel length greater

walls that is vessel Gneturn in comparisons nonliana The investigated. be to need shrubs and lianas of istics

liana from emerges that feature One noteworthy character vessel the and ecology and habit between

lianas. other the for correlations Possible nonlianas. and lianas in same the

than smaller much is species African the for available about and limited, so are Ephedra of surfaces stem the

plants the of size the because probably of lianas groups because interesting is Ephedra in nonlianas and anas

other the of those to comparable features quantitative li between area in conductive difference The nificant.

not have do of Gnetum species The African sig 206). statistically is

nonlianas, and lianas differentiating

1975, (Carlquist of dicotyledons samples woody factor subsidiary a although area, perforation The cies.

and mesic lianas between difference the to similar is spe shrubby of latewood in narrow rather and absent

Gneturn in nonlianas with compared lianas of section to few are Vessels difference. this of most for account

tran mm 2 per area conductive the Still, lianas. in the species lianoid the in vessels latewood Ephedra) (for

density vessel for figures obtaining in excluded were large relatively and numerous The species. nonlianoid

wide rays and the tissue conjunctive the measurement: of as that as large times three than more is species

for adopted conventions the of artifact an part in be lianoid the of 5), 1, col. table mm 2 ; per vessels of ber

may mm 2 ) per 20 to vessels (both close collections turn num mean times perforations of number mean times

Gne

and nonlianoid lianoid between col. 2) 1, (table area perforation (mean transection mm 2 per area tive

density vessel in similarity apparent The 206). 1975, conduc The m). (10.4 species Old World nonlianoid

(Carlquist forms growth dicotyledonous of range a in the of than that greater appreciably is rim) (13.9 lianas

diameter for vessel shown to values similar is ference these of diameter Perforation 1992). (Cariquist dentes

dif 1). This 1, col. table jim; (82 collections gnemon) Scan tribe in available species of seven collections

(G.

arboreal the do jim) than (124 diameter er vessel 11 were there because sample liana the for 1 table in

great appreciably have species Gneturn lianoid The used exclusively were species World Old shrubs. the

understandable. therefore, is, ones the lianoid of that twice than more density vessel a have lianas

well in as Gneturn collections arboreal the in trend the 2): (col. density vessel in difference more much

1975). That (Carlquist dicotyledons in foration plates 1) but (col. diameter vessel in difference is little there

per of simplification accelerated have also er vessels that finds one 1), (table species shrubby of wood the to

Wid 1978). al. et Dickison 1950; Chalk and (Metcalfe Ephedra in lianas of wood the compares one When

Dilleniaceae in and by Tetracera Hibbertia and 984b) 1 mention.

(Cariquist Trimeniaceae in

by Piptocalyx shown brief Markgraf’s since study or comment received

SCIENCES PLANT OF JOURNAL INTERNATIONAL S66 CARLQUIST—ANATOMY OF GNETALES S67 tative wood data for Weiwitschia show it to have a dons, sculpturing in vessels and tracheids characterizes remarkably xeromorphic wood. The mean vessel di species of areas drier and colder than those occupied ameter for a sampling of dicotyledonous desert shrubs by congeners that lack the helical sculpturing (Carl is 29 m (Cariquist 1975, p. 206), whereas the figure quist 1975). Although there is uncertainty about the for Welwitschia is 15 m. To be sure, the former sam- physiological significance of helical sculpturing in sec pie was obtained measuring outside diameter of ves ondary xylem vessels and tracheids of dicotyledons, sels, so that for that sample the lumen diameter (which there is little doubt that it represents a xeromorphic was what was measured for the Gnetales in table 1) adaptation because of the ecological and systematic would be Ca. 24 rim, but that is still significantly wider distribution of this phenomenon. Helical sculpturing than the figure for Welwitschia. The conductive area occurs in tracheids of some conifers, notably Taxaceae per mm2 transection (based on number of vessels per and some Cupressaceae (Greguss 1955). mm2) is low for Welwitschia (.04) but close to figures The mesic ecology of Gnetum is evident in low ves for dicotyledonous desert shrubs (0.18), stem succu sel density: the vessel density in lianoid Gnetum spe lents (.09), and woody species with successive cambia cies is almost the same as for a sampling of dicoty (.06) (Carlquist 1975, p. 206; because vessel wall ledonous lianas (Cariquist 1975, p. 206). The mean thickness was included in vessel diameter in these di- diameter of vessels in G. gnemon (82 jim) does not cotyledon figures, figures based on lumen area as in fall much short of that for a sampling of mesic dicot the Gnetales data would be smaller by perhaps 10%). yledon woody species (108 jim), and the discrepancy The conductive area for liana stems is, by comparison, can be explained by the inclusion of a young stem 0.36 mm2 per mm2 transection (Cariquist, 1975, p. sample and a shrub sample in the G. gnemon survey. 206). However, tracheids are likely quite effective in The vessel diameter of Gnetum lianas (124 jim) is less conduction in Welwitschia and are Ca. three times as than outside vessel diameter for dicotyledon lianas numerous as vessel elements in Welwitschia secondary (157 jim, with lumen diameter probably as much as xylem (tracheids were not included in the estimate of 10 jim less than 157jim). However, again taking into conductive area per unit transection, only vessels). account some immature liana samples—notably the The vessel element length of Welwitschia (508 lim; African Gnetum species—G. gnemon seems to fit the table 1, col. 3) does not seem short by comparison to templates for mesic woody dicotyledons. that of dicotyledonous desert shrubs (218 aim; Carl Phylogenetic conclusions quist 1975, p. 206). That length is shorter than the vessel element length for shrubby species of Ephedra The uncertain nature of relationships of Gnetales to (585 I.tm; table 1, col. 3) and is less than half the vessel other seed plants remains a central interest. The value element length of any Gnetum species. The mean ves of data from morphology and anatomy in this respect sel lumen diameter of dicotyledonous desert shrubs is has not lessened but has increased because at least sev ca. 24 aim; the vessel lumen diameter of Ephedra is eral extinct groups of seed plants may be the sister slightly larger (nonlianoid species, 32 m; lianoid spe groups closest to Gnetales. We can continue to accu cies, 38 pm), but the order of magnitude is compara mulate anatomical information both on these sister ble: few mesic dicotyledonous trees have vessel di groups and on Gnetales, but DNA data for the extinct ameter less than 100 jim (Metcalfe and Chalk 1950). groups are not available. The importance of this cir As in Welwitschia, we cannot estimate the likely con cumstance cannot be overemphasized, because exam ductive capabilities of tracheids as compared to those ples of the effect on phylogeny of inclusion versus of vessels in Ephedra or Gnetum. Comparisons with exclusion of DNA data in cladograms based on several conductive areas per unit transection of dicotyledon data sets can be cited. Such examples are shown in the woods with tracheids, dicotyledon woods with libri cladograms of Albert et al. (1994), Doyle et al. (1994), form fibers or fiber-tracheids, or with conifer woods and Nixon et al. (1994) that exclude fossils. In clado where conductive areas are concerned are premature grams based on DNA evidence alone, Gnetales in until we know the role tracheids play relative to ves variably appear closer to angiosperms, sometimes sels in conduction in Gnetales. showing angiosperms as the sister group closest to Welwitschia and many species of Ephedra possess Gnetales. When DNA evidence and macromorphology a feature that is considered indicative of xeromorphy: are combined (Doyle and Donoghue 1992; Albert et helical sculpturing on the inner surfaces of vessels and al. 1994, pp. 549—55 1; Doyle et al. 1994, p. 426), Pen tracheids. In Ephedra, this takes the form of helical toxylales and Bennettitales are shown to be the closest thickenings on the inner surfaces of vessels and of sister groups of Gnetales, with Glossopteridales and tracheids of most of the New World species (Carlquist Caytoniales separated from Gnetales by relatively 1989) and a scattering of the Old World species (Carl small quantitative cladistic values. quist 1992). In Welwitschia, grooves that represent lat eral extensions of pit apertures around the cell occur VEssELs in vessels and tracheids, providing texturally a grooved The most important item from vegetative anatomy wall surface similar topographically, even if different in attempting to decipher the relationships of Gnetales in phylogenetic origin, to the helical sculpturing pres is the nature of the gnetalean vessel. Thompson (1918) ent in vessels and tracheids of Ephedra. In dicotyle and Bailey (1944, 1953) claimed that the angiosperm

evident

plate, perforation

Gnetum the of modification the to according regarded, is 1—4) (figs. Ephedra

accelerated The

xylem. primary

to close vessels xylem of plate perforation foraminate the Thus, argument.

secondary

narrow in

clearly

most Gnetum, in seen be the from excluded not is pitting wall lateral so that

can

still

condition

ephedroid the but 5—8), (figs. plate pitting, wall lateral of, modification a or of, extension

perforation a

simple

result as to so perforations the an represent to considered is plates of perforation the

coalescence

and

enlargement in notably ifications, nature the In turn, plate. perforation the of the nature

mod further

represent would

vessels Gnetum branes. in lie of angiosperms those from separately originated

mem pit

of loss and

pits

wall lateral to compared as have to vessels gnetalean considered 1953) (1944, ley

perforations

the of size in

increase include would plate Bai and (1918) Thompson why reasons central The

perforation

ephdroid the

modifications The above). gymnosperms. of group a vesselless from

cited papers

cladistic

(see Gnetum and Welwitschia arose Gnetales that the idea favor would angiosperms

basal as

Ephedra of

placement cladistic universal and Gnetales in vessels of origin homoplastic whereas

virtually

the with

accordance in Gnetales, of vessels groups, two the of closeness for evidence of piece

from

primitive

modified

as little concept this in garded significant a be would symplesiomorphy a as groups

in Ephedra condition 9).

The (fig. walls lateral major two in the presence Vessel (1982). Sattler

the

on those

like pits

bordered of circular semblage and Muhammad by questioned been has concept This

as an

from derived as hypothesis,

Thompson-Bailey origins. separate had vessel gnetalean the and vessel

10 p.m.

each in

left upper

Bars

pit in membranes.

pores of size

small show to tracheid of end wall pits from s. three n.; AW Oliver, sinense

10, Tetracentron Fig.

intact. are

which of some

least

threads, margo with connected each of center in torus conspicuous showing pits three

1425; Freitag

Wallich,

gerardiana Ephedra 9,

Fig. sections. radial on seen as tracheids from pits of 10 photomicrographs SEM Figs. 9,

I -‘k •‘

SCIENCES PLANT OF JOURNAL INTERNATIONAL S68 CARLQUIST—ANATOMY OF GNETALES S69

in coalescent-foraminate conditions (figs. 5, 6) as well 1994). However, should shape be the central issue? as in simple and near-simple (figs. 7, 8) conditions, is The circular shape of gnetalean pits is contrasted by easily explained in terms of flow rate. With minute these authors with the scalariform type of pitting wide foliar surface, selective pressure for simplification of ly thought to be primitive in angiosperms. However, the perforation plate of Ephedra is minimal, whereas if examined in terms of adaptations to function that the greater probable transpirational rates of the broad underlie phylesis, shape may not be the primary con leaves of Gnetum favor simplification of the perfora sideration. The gymnospermous tracheary element pit, tion plate to accommodate peak flows in vessels. as exemplified by those of Ephedra (fig. 9), contains The perforation plate of Welwitschia is not generally a thick central torus, suspended by margo threads. The entered into this sequence, presumably because vessels function of the torus (Frey-Wyssling 1976) is closure in that species are so different from those in Ephedra of the pit aperture during aspiration, when a tracheid and Gnetum. Also, the consequence of considering that has filled with air is sealed off, by displacement Ephedra the basal genus of Gnetales means that in of tori so as to close pit apertures, from tracheary el determining relationships of Gnetales, the nature of the ements that are still functioning. Moreover, the margo vessel in Ephedra is more important than that of Wel strands feature wide spaces, spaces wide enough to witschia. Muhammad and Sattler (1982), however, accommodate passage of colloidal gold particles concentrate on attempting to show a morphological (Frey-Wyssling 1976) or other objects about 0.2 im continuum between vessels of selected angiosperms in diameter (Panshin and De Zeeuw 1980). These and those of Gnetum rather than a continuum between spaces are much larger than the micropores in pit Ephedra or Welwitschia vessels and those of angio membranes of angiosperms (fig. 10; pits from an end sperms. Muhammad and Sattler (1982) designate cer wall of a Tetracentron tracheid are shown there, but tain perforation plates of Gnetum as “scalaroid” (e.g., lateral wall pits would be quite similar in this respect). fig. 7), and apparently present these plates because The margo strands, by their slender, flexible strandlike they are considered to be suggestive of what vessels nature and the way they suspend the torus, allow for intermediate between those of Gnetales and those of movement of the torus and thus closure of the gym primitive angiosperms might be like. These plates do nospermous pit during aspiration. The angiospermous not appear to me to be scalariformlike but, rather, can pit (fig. 10), on the other hand, lacks a torus and is, in be more accurately categorized as “foraminate coales any case, generally too rigid to function in aspiration. cent,” exactly what would be expected in a phyloge Exclusion of potential air entry from a deactivated tra netic series in which an ephedroid perforation plate is cheid of this type into a functioning water-filled tra undergoing simplification in response to adaptation to cheid is prevented by the excessively small size of the higher peak flow rates. micropores, through which air bubbles cannot pass Muhammad and Sattler (1982) have chosen for (Carlquist 1988a, p. 108; Jarbeau et al. 1995). A cir comparisons with Gneturn a series of angiosperms that cular shape is irrelevant to the primitive angiosperm are not at all basal within angiosperms in terms of pit because a movable torus is not present; instead, the contemporary phylogenies, either those that are based scalariform shape covers the lateral width of the wall on cladistics (e.g., Qiu et al. 1993) or those that use efficiently, maximizing pit area on a tracheid and con more traditional methods (e.g., Thorne 1992). Vessels tact with adjacent cells. Thus, water handling and con of Juglandaceae, Myricaceae, and Salicaceae are used ductive safety mechanisms of the circular gymnosper by Muhammad and Sattler (1982) for purposes of mous pit and the scalariform angiospermous pit comparison, although those families seem, on the basis represent two alternative functional modes, and the na of our current ideas of their phylogenetic placement, ture of this difference should not be described primar unlikely to retain perforation plates like those of an ily in terms of pit shape. The different shape is, as we cestral angiosperms. have seen, a by-product of differences in physiological However; additional features in vessel phylesis with mechanisms, not a cause for them or a fundamental regard to Gnetales are worthy of consideration and phylogenetic feature in its own right. have not been discussed to date to any appreciable The discovery of tori in tracheary elements of Gne extent at all. The circular bordered pits on lateral walls turn (Carlquist and Robinson 1995; Carlquist 1996a, of Ephedra, Gnetum, or Welwitschia vessels are mark 1996b) is of significance because thus the pits of Gne edly unlike those on lateral walls of angiosperm ves turn tracheids are not transitional from those of cycads sels considered to be primitive. In turn, the primitive to those of conifers, as thought by Frey-Wyssling gnetalean tracheid from which gnetalean vessels are to (1976, p. 61), and the simplified perforation plates of be derived bears little resemblance to tracheids widely Gnetum that allegedly look transitional (“scalaroid”) considered to be primitive in angiosperms. This con to scalariform angiosperm plates must be viewed as trast is stressed by the juxtaposition of figs. 9 and 10 modifications of lateral wall pitting that, in Gnetum, is but needs additional explanation. A difference in the not at all like that of angiosperms. The fact that tra shape of perforations or the shape of pits of lateral cheary elements of Gnetum are not fundamentally dif walls between Gnetales and angiosperms has been ferent from those of Ephedra can be considered evi considered by many authors, especially recent seed dence for monophyly of Gnetales. Thus, a transitional plant cladists (e.g., Doyle et al. 1994; Nixon et al. position for Gneturn between more primitive Gnetales S70 INTERNATIONAL JOURNAL OF PLANT SCIENCES

Figs. 11, 12 SEM photographs of walls of primary xylem tracheary elements from radial sections of stems of Gnetum leyboldii, McPherson 10003. Fig. 11, Pit membranes lacking in the circular pitlike structures, top and bottom, which therefore are perforations. Fig. 12, Smaller circular bordered pits intercalated into the helical thickenings; a pit membrane is clearly present in the pit at left, and neither of the pitlike structures is likely a perforation. Bars at upper left = 10 p.m. and angiosperms is not supported. There is similar ev conifers, Ginkgo, and Gnetales is that circular bordered idence in phloem: according to Ray F Evert (personal pits are intercalated into these bands. This situation has communication), ultrastructure of sieve elements of been noticed for many years (Bierhorst 1960). Such Gnetales is like that of gymnosperms rather than that intercalated bordered pits are not present in the pri of angiosperms. mary xylem of angiosperms. Thus, those who visual A highly significant formation in the primary xylem ize Gnetales as transitional to angiosperms are faced of Gnetales also offers evidence about the phyloge with explaining the presence of this neglected feature netic position of Gnetales. In metaxylem tracheids and in Gnetales. vessel elements of Gnetum (fig. 11, 12) and Ephedra, I hypothesize that the presence of circular bordered bordered helical thickenings, composed of lignified pits intercalated into the helical secondary wall bands secondary wall material, are attached to the thin pri of primary xylem tracheary elements of conifers, mary walls, just as in many vascular plants. As has Ginkgo, and Gnetales is related to functions that have been described extensively, the gyres of helical thick not yet been considered, largely because emphasis has enings in such metaxylem elements can stretch out, been placed on this feature from a descriptive or tax accommodating increase in length by the tracheary el onomic point of view. One functional possibility for ements. A special feature of the helical bands of sec these circular pits is suggested by their structure in ondary wall material in the metaxylem tracheids of figure 11, in which the two circular pits are, in fact, CARLQUIST—ANATOMY OF GNETALES S71 not pits, but perforations. Lack of pit membranes is existing with fiber-tracheids in a wood in this well shown for these two circular areas, and earlier instance—do not appear to be basal within studies by means of light microscopy were not able to angiosperms. Among dicotyledons that appear at all demonstrate lack of pit membranes with any certainty. close to being basal in recent phylogenetic treatments, Presumably, perforations of this sort would occur in dimorphism of this kind has been identified only in primary xylem of Gnetum and Ephedra but not in Austrobaileyaceae (Carlquist 1 988c), and such dimor Ginkgo or conifers, which are vesselless. phism has not been identified in any gymnosperms A second likely functional significance of the inter other than Ephedra and Gnetum. Axial parenchyma is calated circular bordered pits of primary xylem ele present in numerous gymnosperms and in primitive ments of Gnetales has to do with the torus-margo or dicotyledons, and it occurs in Welwitschia (Cariquist ganization of secondary xylem tracheary element pits. and Gowans 1995) and in all species of Gnetum (figs. By forming the circular bordered pits, the conductive 13—15) and in a few species of Ephedra (Carlquist capabilities of the large spaces that characteristically 1992). In addition to differing from wood of other occur among margo strands are available. Also, the pit gymnosperms and from woody dicotyledons other aspiration mechanism, by virtue of the presence of a than Austrobaileya and some more specialized phylads torus, is also potentially present. The primary xylem in having tracheid dimorphism, Gnetum and Ephedra elements evidently have negligible microporosities in woods are further distinct in the distribution of fiber the lateral primary wall between the helical gyres of tracheids with respect to tracheids. In dicotyledons that secondary wall material, according to my SEM pho have tracheid dimorphism, the tracheids occur in a vas tographs (figs. 11, 12). Thus, conduction capabilities icentric pattern, whereas fiber-tracheids are distal to of the primary xylem tracheary elements with the in the vessels (Carlquist 1985). In Gnetum gnemon, fiber tercalated circular pits are greatly enhanced by the tracheids appear distributed randomly with relation to availability in these pits of the spaces between the mar- tracheids; in the lianoid Gnetum species, fiber-trache go strands. This potential mechanism for enhancement ids tend to be in radial files alternating with tracheids of conduction is available to Ginkgo and conifers, as (fig. 16). In Ephedra, fiber-tracheids are arranged dif well as Gnetales, and has not received comment as a fusely or in tangential bands (“diffuse-in-aggregates” functionally valuable feature. is the term applied to that distribution, but this term is normally applied to axial parenchyma, not to fiber-tra OTHER XYLARY FEATURES cheids). In no species of Ephedra or Gnetum was a Ephedra, Gnetum, and Welwitschia were claimed, vasicentric distribution of tracheids seen. in almost all earlier literature, to have only two types The observation that both Ephedra and Gnetum of tracheary elements: tracheids and vessel elements. have fiber-tracheids together with tracheids, a condi Axial parenchyma was claimed to be present in Ephed tion otherwise unreported in gymnosperms, suggests ra and Gnetum (Martens 1971), although drawings by this feature may be plesiomorphic in Gnetales, in Greguss (1955) claim fiber-tracheids for Gnetum gne which case lack of fiber-tracheids in Welwitschia mon. Fiber-tracheids are not present in Welwitschia, would have to be interpreted as an autapomorphy. but fiber-tracheids are present in all species of Ephedra Gnetales are distinctive in having both multiseriate and Gnetum (fig. 13) studied thus far. The phyloge and uniseriate rays, although in Ephedra, multiseriate netic significance of this is interesting in several re rays predominate and uniseriate rays are relatively spects. Dimorphic tracheary elements—tracheids co scarce. In Welwitschia, rays are more difficult to ob

Figs. 13—16 Light photomicrographs of Gnetum to show differentiation between cell types. Fig. 13, Gnetum gnemon, Carlquist 8088; radial section of root showing, bottom to top, a tracheid, two fiber-tracheids containing septa and starch, and a pair of cells from an axial parenchyma strand, separated by a lignified wall, which is vertical in this photograph. Fig. 14, Gnetum cuspidatum Blume, transection of stem, showing three cell types in axial secondary xylem: tracheids have thick walls; fiber-tracheids have walls of intermediate thickness; and axial paren chyma cells (some of which contain crystals) have very thin walls, some of which are not clearly delineated. Fig. 15, Gnetum schwackeanum, Farifio 425; transection of stem, showing a portion of secondary xylem in which axial parenchyma cells (thin gray walls) are relatively abundant. Fig. 16, Gnetum leyboldii, McPherson 10003; transection of juncture between secondary phloem (above) and secondary xylem (below), to show that the files of phloem parenchyma (narrower cells with thin walls) are intercontinuous with files of narrow cells in the secondary xylem. Wide cells in the secondary phloem = sieve cells; wide cells in the secondary xylem = tracheids. Further explanation in text. Figs. 13, 14, 16, Magnification scale above figure 7; fig. 15, scale above figure 15 (divisions = 10 p.m).

Figs. 17—20 Light photomicrographs of Stem transections of Gnetum (figs. 17—19) and Ephedra. Fig. 17, Gnetum schwackeanum, Farino 425; portion of outer stem to show (top to bottom), sclerenchymatous cylinder, lateral meristem region, recently formed vascular strand (five vessels visible in secondary xylem), and conjunctive tissue in which several laticifers are present. Fig. 18, Gnetum cuspidatum, Carlquist 8091; portion of vascular strand (phloem fibers are dark, near center), above which and to the right of which are radially oriented files of cells related to lateral meristem activity. Fig. 19, Gnetum latifolium Blume, Carlquist 8087; transection of outer portion of underground stem; a thin gray band about one-fourth from the top of the photograph delimits phellem (above) from cortex; in cortex, there are scattered gelatinous fibers and (lower right) a few sclereids. Fig. 20, Ephedra cal(fornica, cortex of primary stem; arrows point to gelatinous fibers, which are pale gray. Figs. 17, 19, Scale above figure 17 (divisions = 10 m); figs. 18, 20, scale above figure 15. SZ’NIDS INVId 1O 1VN1f1Of ‘IVNOIIVNINI ZLS CARLQUIST—ANATOMY OF GNETALES S73

“4:

)f 1%i’

F •?;

Gne

Merrill.

klossii Gnetum in

astrosclereids ray liar of ira- distribution vasicentric without yet

tracheids,

pecu

of presence the is

discovery await may interest fiber and tracheids both have Ephedra

and Gnetum

features

some that

indication One present. at tures that demonstration the and Gnetum of species five least

fea these

delimit to

poor

is too

Gnetum and Ephedra at of pits in tori of demonstration the by

reinforced

sampling

part, In uncovered.

were levels fragenenc is interpretation This rays. uniseriate and

multiseriate

in at

significance

taxonomic be

to likely features both with group gymnosperm vesselless a from

nated

few

very level, species

a at

wood and bark of survey origi have to appear Gnetales evidence.

cited ously

the

from

emerged

contexts

ecological and logenetic previ as well as concepts new of basis the

on here,

phy

major in valuable

information

much Although supported are Gnetales in and angiosperms in dently

bark.

and

phloem, wood, indepen arose vessels that 1953) (1944,

Bailey of

of cells

within

has crystals Gnetum

localities. mesic and (1918) Thompson of opinions The opinion. my in

into

shifted phylad that

Gnetum of ancestors in lost angiosperms, with synapomorphies any indicate fore,

feature

plesiomorphy, a

is Welwitschia and Ephedra there not, do Gnetales of features stem and Wood

in crystals

intercellular minute the of occurrence haps autapomorphies.

Per genera. two

these in reported form the least in at of series a but or symplesiomorphies synapomorphies

plants,

vascular

unknown otherwise is feature This not likely are Gnetales within activity cambial in tions

features.

lining

intercellular crystals oxalate calcium varia the Therefore, cortex. than rather phelloderm

intercellular

minute

of occurrence Welwjtschja: and from derived are however, Welwitschia, in files stem

Ephedra

link to

appears decades earlier in reported not men- lateral The species. lianoid the in those of igin

feature

One peculiar

phelloderm. from meristem lateral or with compared delayed much is evidently cambia

origin and

fibrosclereids, crystal-bearing large of new these of origin of the time although involved, is

presence

cavities, secretory of presence tracheids, and tissue cortical in that similar is gnemon G. of the bark

vessels surfaces on

inner thickenings) than (rather in cambia new of origin The l996b). 1996a, Cariquist

grooves vessels, of

walls lateral of those like plates 1995; Robinson and (Carlquist studies recent more

perforation simple

with vessels fiber-tracheids, of lack in confirmed as and (1916) La Rivière by claimed as

are

Welwitschia

autapomorphies the likely Among cortex, inner in is species lianoid Gnetum all in tivity

ways.

numerous in

stock

gnetalean ancestral an from ac meristem lateral of origin The stem. aging of the

has

departed it

suggests features) bark other lacks but conformation contorted increasingly to owing entation

phellem has

(which Welwitschia in autapomorphies ori cambial of to distortion be appear conditions those

in richness

however:

entertained, be may planations category; this in Ephedra for (1993) Aloni and dun

Alternative genera. two the

between resemblance a Lev-Ya by described modifications cambial the place

suggest

fibers,

gelatinous distributed diffusely of ence do not I activity. meristem lateral of kind a from rived

pres as

such

features,

bark Several plates). perforation de parenchyma in originate that 18) 17, (figs. cambia

foraminate and

tracheids, and fiber-tracheids both of of successive presence the is significance phylogenetic

presence

(e.g.,

and Gnetum Ephedra between affinity potential major of feature stem or wood other The

suggest of papers,

series in this reported newly are sperms.

that

of those

some especially wood features, Several angio with only Gnetales link would that apomorphy

altogether.

vesturing

lack to judged was studied cies syn a as interpreted not best therefore is feature this

spe but no

inconspicuous, quite is vesturing which in and to Gnetales, close considered commonly nosperms

species some in

find

vessels can one with laticifers, As gym among widespread appears rays uniseriate with

Gnetum.

for

autapomorphy

likely a also is vessels of intermixed rays of multiseriate presence Thus, rays.

pits in

Vesturing Gnetum. of

species all in velopment multiseriate some least at having as Caytoniales score

de of stage

some at

present be to likely be to sumed (1986) Donoghue and Doyle and 1953), (Bose eriate

be should

laticifers

stages; of developmental study tris to uniseriate rays has Bucklandia 1957), nu-Mittre

without of Gnetum

species any for claimed be cannot (Vish ones uniseriate as as well rays multiseriate and

absence and

development, to

related a feature ered biseriate some has Pentoxylon 1906). (Wieland titales

consid

be must thus

Laticifers species. Gnetum some Bennet of wood in the present are rays biseriate and

roots

and

stems older in

evident not are ticifers uniseriate Both Gnetales. of groups sister be to likely

la 1971),

(Martens

commonly laticifers contain plants gymnosperms of orders those especially cladograms,

Gnetum of

stages

younger developmentally though recent in to Gnetales close placed are that nosperms

Gnetum. to

restricted feature a of example good gym the in present are rays uniseriate and tiseriate

a are

17)

(fig.

Laticifers anatomy. xylem and stem mul both is whether pertinent More 1968). (Greguss

respect

with

autapomorphies in are rich Gnetales cycads in is common of rays types both of Presence

appreciated. been generally has than gymnosperms Gnetales within Relationships

within widely more occur may it addition, In Gnetales.

data.

wood by supported

thereby are gymnosperms of in feature plesiomorphic a be may it but angiosperms,

group

vesselless

is Gnetales

of group sister likely the to resemblance of point a as cited been has Gnetum in

that

indicate that

(1994) al. et

Nixon and (1994), al. et rays uniseriate and multiseriate both of presence The

Doyle

(1994), al. et

Albert

by cladograms The phism. rays. uniseriate as begin may of these a few least at

dimor tracheid

have

that angiosperms all as in cheids

but present, are rays multiseriate certainly and serve,

SCIENCES PLANT OF JOURNAL INTERNATIONAL S74 CARLQUIST—ANATOMY OF GNETALES S75

turn gnernon appears rather different from the lianoid patterns within these two remarkably widespread and species of Gneturn in bark and wood characters, but divergent genera, and even our concepts about what study of the sister species of G. gnernon, Gneturn cos constitutes a species within these genera are tentative. taturn K. Schum. is needed, and much infraspecific Acknowledgments diversity within G. gnernon remains to be explored. For grants that Attention should be focused on whether Markgraf’s permitted collection of specimens of Gneturn and Welwitschia, I express my (1930) sections and subsections—which correspond appreciation to the National Geographic Society and the American with habit and geography—are confirmed by newer Philosophical Society. Collections by Gordon Mc data. The placement of the New World lianas in the Pherson were made possible through the courtesy of same section as G. gnernon rather than in the section Dr. Peter H. Raven. Dr. Jack Fisher shared material of that includes the Indomalesian and Asiatic lianoid Gneturn rnicrocarpurn. Living material of Gneturn was Gneturn species is one feature of Markgraf’s (1930) provided by Stephen Morgan of the Botanic Garden system that invites reinvestigation. Although wood and of the University of California, Riverside. Dr. Dennis bark data seem to offer a number of features of major Stevenson of New York Botanic Garden aided with phylogenetic and ecological significance, molecular identifications and material from the herbarium of that data will likely be of prime importance for infrageneric institution. The studies were begun at Rancho Santa systematics of Ephedra and Gneturn. At present, we Ana Botanic Garden, which aided by providing sup have few reliable hints about evolution and speciation plies. Literature cited

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SCIENCES PLANT OF JOURNAL INTERNATIONAL S76