IAWA Bulletin n.s., Vol. 1 (3), 1980 87

WOOD ANATOMY OF THORNEA, INCLUDING SOME COMPARISONS WITH OTHER

by

Arthur C. Gibson Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona 85721, U. S. A.

Summary The wood anatomy of the new Thor­ num virginicum (Holm, 1903) lacked descrip­ nea (Hypericaceae) is described and compared tions of secondary tissues. Nevertheless, with that of other presumed relatives in the sections of hypericaceous stems are available in family. Woods of Thornea are very similar to wood collections, and the goal of this study those of and Triadenum but quite was to describe the woods of Thornea and to dissimilar to those of Cratoxylum, with which make comparisons with its putative relatives. Thornea presumably shares common ancestry. Materials and Methods Introduction Wood specimens from mature of Breedlove and McClintock (1976) proposed Thornea calcicola (StandI. & Steyerm.) Breedl. the genus Thornea to include two evergreen & McClint. 7 cm and 4 cm in diameter were fruticose species from Chiapas, Mexico and collected in Chiapas and air dried by Dr. adjacent Guatemala that were originally de­ Dennis Breedlove (36973, 37070, OS). These scribed as species of Hypericum. Thornea has specimens were also those used in the generic nine fertile stamens grouped in three fasci­ description. In addition, Breedlove provided cles of three each, three persistent and free small stems of T. matudae (Lundell) Breedl. & styles, tricarpellate ovaries developing into McClint. liquid-preserved in formalin-acetic three nearly separate dehiscent capsules, and acid-alcohol (Breedlove 40408, OS). Wood pink and white petals with parallel stria­ samples of T. calcicola have been deposited in tions, features characteristic of Triadenum. the Madison Wood Collection (MADw). On the other hand, Triadenum are herbaceous Air-dried blocks were sectioned after re­ perennials of wet temperate habitats, quite hydrating, on a sliding microtome and stained unlike the habitus of Thornea. with safranin. Macerations were prepared by Based on the studies by Robson (1956, Jeffrey's macerating fluid and used to ob­ 1972), Wood and Adams (1976) and Breedlove tain 50 measurements of length for elements, and McClintock (1976) suggested that Triade­ whereas other features were obtained from num and Thornea, respectively, are closely sections. Young stems of T. matudae were em­ related to Cratoxylum of tribe Cratoxyleae, bedded in paraffin, sectioned at 15 J.Lm, and subfamily Hypericoideae, having an indepen­ stained with safranin and fast green. These dent origin from Hypericum, which is external­ microslides were examined but not used in the ly similar to Triadenum. Robson (1977) generic diagnosis for older woods. Nonethe­ elaborated on the close relationships of Triade­ less, woods of the two species are qualita­ num and Thornea to Cratoxylum and Eliaea tively very similar. and not to Hypericum, and he defined three Intergeneric comparisons with Hypericoi­ tribes, Hypericeae, Vismieae, and Cratoxyleae, deae were made using wood microslides borrow­ in subfamily Hypericoideae to recognize those ed from the Harvard Wood Collection (from differences in flower colour, staminal composi­ Vestal, 1937) and Rancho Santa Ana Botanic tion, and fruit and seed features. Garden, Claremont, California. Materials exam­ Vegetative anatomy of Hypericoideae is very ined include species of Harungana, Psorosper­ poorly known. Useful surveys on woods of mum, and Vismia of tribe Vismieae; Triadenum Hypericaceae (including Guttiferae and Hyperi­ virginicum and numerous species of Cratoxy­ caceae s.s.) are in Vestal (1937), Record and lum of Cratoxyleae; and over 100 species of Hess (1943), and Metcalfe and Chalk (1950), Hypericum, including the segregate genus and Baas (1970) has provided illustrated Ascyrum (Adams & Robson, 1961), especially descriptions of woods in Cratoxylum and the least derived and most woody sections of Eliaea. The only anatomical study on Triade- the genus (Robson, 1977).

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Fig. 1-4. Thornea calcicola. - I: Transverse section, showing diffuse porous wood with faint growth rings; x 50. - 2: Tangential section, in which uniseriate and multiseriate rays can be observed; x 50. - 3: Transverse section; tissue is composed of vessels, libriform fibres, and rays but not axial paren­ chyma; x 540. - 4: Tangential section, in which vessel-element length can be observed; x 540. -­ Fig. 5-6. Triadenum virginicum (Hw 5649). - 5: Transverse section at same magnification as Fig. 3, showing general similarities in these two woods. - 6: Tangential section as in Fig. 4; x 540.

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Observations Axial parenchyma absent. Rays exclusively uniseriate, ca. 20/mm. Cells Wood diagnosis for Thomea (Figs. 1-4) exclusively upright and containing resin. Macroscopic description - Wood moderately Secondary xylem nonstoried. light, reddish brown to cinnamon brown in col­ our, no distinctive figure. Heartwood not Secondary xylem of Hypericum (Hw; those clearly differentiated. Rays not conspicuous used in Vestal, 1937; Figs. 7-9) on the end grain. Microscopic description - Growth rings Microscopic description - Growth rings generally not well defined, sometimes observed presen t, weakly defined by strongly lignified in semi-ring porous species, e.g., H. patulum; wood fibres. Pores diffuse, 75-110/mm2, soli­ rarely distinctly marked by fibre dimorphism, tary and in radial pore chains and pore clus­ e.g., H. densiflorum. Pores typically diffuse, ters mostly of 2-4 but chains up to 14. Pores less commonly semi-ring porous, very numer­ irregular in outline; diameters in longest di­ ous, in many greatly exceeding 200/mm2, rection 18-81 j.lm, with means 40-59 j.lm. Walls solitary and in radial pore chains and irregular about 3 j.lm. Vessel-element length medium­ pore clusters. Pores typically irregular in ou t­ sized, 226-712 j.lm, with means 425-507 j.lm. line; maximum diameters in longest direction Perforation plates simple, rarely aberrant multi­ 75 j.lm. Walls usually very thin, mostly 3 j.lm or perforate, mostly oblique and having short to less. Vessel-element length very short, mostly fairly long pitted tails. Intervascular pitting mul­ less than 250 j.lm as measured in tangential sec­ tiseriate alternate and bordered; pits mostly 2- tion. Perforation plates simple, rarely multi­ 4 j.lm across with a slit-like aperture, especially perforate, oblique to near transverse and ap­ elongate on tails. Pits to parenchyma as be­ pearing to have relatively short tails or none tween vessels or more elongate. Tyloses absent. at all. Intervascular pitting alternate and Wood fibres libriform and mostly septate; bordered; pits mostly 4 j.lm or less; some with wall thickness 4-6 j.lm. Maximum fibre diame­ large bordered pits to 6 j.lm, tending to have ter 30 j.lm. Fibres very short, 425-971 j.lm, fewer longitudinal rows; pits mostly circular means 665-719 j.lm. Average fibre-vessel with slanted slit-like apertures. Tertiary helical element length ratio 1.5. thickenings and tyloses present in some species. Axial parenchyma absent. Fibre-tracheids and libriform fibres even in Rays uniseriate and narrow multiseriate (to the same wood, in which very thick-walled ele­ 4), 16-22/mm, often difficult to distinguish ments have simple pits and fairly thin-walled in transection. Uniseriate rays homocellular, ones have prominent circular bordered pits. composed of upright cells; very low, generally Walls of libriform fibres mostly 2-4 times less than 10 cells high. Multiseriate rays hetero­ thicker than vessel walls, but in some both cellular with mostly square cells; 250-1,900 walls are equal; where fibres have thin walls j.lm high. Some ray cells with resin and starch and lack lignification, vessel walls have the grains. thicker walls. Fibre-tracheids usually associated Wood nonstoried. with vessels (Vestal, 1937); these cells, called vascular tracheids (Baas, 1970), are narrower Secondary xylem of Triadenum virgin/cum and longer than vessel elements and have (Hw 5649, sections only; as Hypericum virgin­ pointed end walls. icum; Figs. 5-6) Axial parenchyma absent. Microscopic description - Only one growth Rays uniseriate except in exceptional cir­ layer present. Pores diffuse, ca. 500/mm2, soli­ cumstances where branch traces diverge through tary and in radial pore chains and small pore secondary tissues; rays low to extremely low, clusters. Pores irregular to somewhat angular composed mostly of square cells; rays often in ou tline; diameters in longest direction homocellular with upright cells in stems with 20-50 j.lm. Walls 1-3 j.lm. Vessel-element very little secondary growth. Resin present in length very short, mostly 200-250 j.lm as many species. measured in tangential section. Perforation plates exclusively simple, mostly oblique and Wood diagnosis for Vismieae (Figs. 10-12) appearing to have relatively short tails or none Microscopic description - Growth rings at all. Intervascular pitting multiseriate alternate generally present, faint, marked only by thick­ and bordered; pits mostly 2-4 j.lm across with er fibres. Pores diffuse but often unevenly slanted slit-like apertures. Tyloses absent. distributed in radial or oblique bands; pores Wood fibres libriform nucleate and frequent­ solitary and in small multiples, the latter with ly septate; wall thickness 3-5 j.lm. Maximum 1-4 wide ~Iements and sometimes several ex­ fibre diameter 20 j.lm. Fibres very short. tremely narrow ones. Pores circular to radial-

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Downloaded from Brill.com09/24/2021 10:24:58PM via free access IAWA Bulletin n.s., Vol. 1 (3), 19BO 91 ly ovoid in outline; diameters medium sized, wider pores than any other species and tend to maximum observed 240 Ilm in Vismia ferrugi­ have more paratracheal parenchyma, whereas nea and Psorospermum androsaemifolium, banded apotracheal parenchyma and vascular means of outer wood 90-lBO Ilm, less in tracheids are less developed. younger stems. Walls mostly 4-6 Ilm, occasion­ ally thicker. Vessel-element length (observations Discussion from tangential sections) moderately short to Secondary xylem of Thomea, Triadenum, medium-sized, mostly 250-500 Ilm. Perfora­ and Hypericum is organized on a common tion plates simple, oblique to nearly transverse. design, having very numerous, short and Intervascular pitting multiseriate alternate and narrow vessel elements and no axial parenchy­ bordered; pits mostly 3-6 Ilm across with a ma. All have very similar uniseriate rays, but slit-like aperture. Tyloses abundant in some. woods of Thomea are clearly distinguishable Fibres composing wood matrix libriform, by the presence of multiselliate rays. Thomea often in discrete radial rows. Wall thickness also has the longest vessel elements. Cellular mostly 2-4 Ilm, to 7 J.Iffi in Psorospermum features of xylem in Thomea and Triadenum androsaemifolium. Maximum fibre diameter are strikingly similar, even though species of 20-30 Ilm. Libriform fibre length apparently Thomea are large tropical species with abundant short to very short. Fibre-tracheids (vascular wood production whereas Triadenum are tracheids) typically present in radial or oblique temperate, rhizomatous herbaceous perennials. bands with vessels, often seen in transection Triadenum has extremely abundant vessels, a connecting adjacent pores; length very short, condition found elsewhere in Hypericaceae somewhat longer than adjacent vessel elements. (incl. Guttiferae) only in certain species of Axial parenchyma abundant, apotracheal in Hypericum. In Hypericum, woods most closely tangential bands, becoming para tracheal where similar to Thomea are found in sections bands touch pores; apotracheal diffuse paren­ Campylosporus, Ascyreia, Brathys, Adenosepa­ chyma rarely observed. Resin present in some lum, and to lesser degrees Spachium and species. Myriandra, which Robson (1977) treats as the Rays uniseriate and narrow multiseriate 10- least specialized groups of the genus. Several IB/mm; heterogeneous type II; cells ofuniseri­ of these sections occur in the American tropics, ate rays mostly square or upright, tending to overlapping in distribution with Thomea. homocellular. Some rays with resin deposits. On the other hand, woods of Thomea are Wood nonstoried. fundamentally dissimilar to those of Cratoxy­ lum, Eliaea, and Vismieae, which have very Woods of Cratoxylum and Eliaea (Figs. 13-15) few, relatively wide pores, axial parenchyma in Wood descriptions of Cratoxylum and Eliaea conspicuous tangential bands, and a uniform by Baas (1970) compare closely to those pre­ type of heterogeneous rays. Comparisons with sented here for Vismieae (compare Figs. photomicrographs in Vestal (1937) reveal that 10-15). Eliaea is exceptional in having only this design is very reminiscent of woods in fibre-tracheids and no vascular tracheids or Calophyllum, less so to those of Garcinia and libriform fibres. In Cratoxylum, the most Platonia, and is apparently a widespread pat­ remarkable differences occur in section Isopte­ tern in Hypericaceae with simple perforation rygium, two evergreen species in Malesia. plates (Record & Hess, 1943; Metcalfe & Woods of C. arborescens and C. glaucum have Chalk, 1950).

Fig. 7-15. Woods of other Hypericaceae. All x 50. - 7: (Hw 5632), trans­ verse section, having general features of Thomea but some vascular tracheids (fibre-tracheids) asso­ ciated with vessels. - B: (Hw 549B), transverse section, in which growth rings are fairly well defined. - 9: (Hw 5619), tangential section, showing low uni­ seriate rays and extremely short vessel elements. - 10: Psorospermum androsaemifolium (Hw 5462), transverse section; pores are few in number and moderately wide, and apotracheal parenchyma oc­ curs in tangential bands. - 11: Vismia ferruginea (Hw 5699), transverse section, similar in organiza­ tion to Fig. 10. - 12: Psorospermum androsaemifolium, tangential section, showing uniseriate and multiseriate rays along with apotracheal parenchyma. - 13: (Hw 5492), transverse section, in which the tangential bands of axial parenchyma touch vessels. - Fig. 14-15. (USw 13310). - 14: Transverse section, showing wide, mostly solitary ves­ sels with paratracheal aliform parenchyma instead of apotracheal bands. - 15: Tangential section, illustrating uniseriate and multiseriate rays, para tracheal parenchyma, and short vessel elements.

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A conclusion that wood anatomy negates from Indo-Malesia (Guttiferae). Blumea 18: relationships between Cratoxylum and the 369-39l. Thomea and Triadenum phylad is contradicto­ Breedlove, D.E. & E. McClintock. 1976. Thor­ ry to the systematic views of Robson (1977), nea (Hypericaceae), a new genus from who assigns Triadenum and Thomea to tribe Mexico and Guatemala. Madrofio 23: 368- Cratoxyleae. Robson characterizes Cratoxyleae 373. by capsular fruits with winged seeds, white and Holm, T. 1903. Triadenum virginicum (L.) pink petals, and interstaminal glands. Any of Raf.: a morphological and anatomical these features, even wood structure, could have study. Amer. 1. Sci. IV. 16: 369-376. arisen by parallel evolu tion; therefore, Ro bson Metcalfe, C.R. & L. Chalk. 1950. Anatomy of places great emphasis on similarities between the Dicotyledons. Clarendon Press, Oxford. Triadenum and Cratoxylum in vascularization Record, S.l. & R.W. Hess. 1943. Timbers of of sterile and fertile fascicles, notwithstanding the New World. Yale Univ. Press, New the complexity in Cratoxylum. However, to Haven. date no one has determined whether this Robson, N.K.B. 1956. Studies in the genus vascular pattern occurs elsewhere in this Hypericum. Ph.D. thesis, Edinburgh Univ. family, in which most genera have not been - 1972. Evolutionary recall in Hypericum examined. Consequently, the phylogenetic (Guttiferae)? Trans. Bot. Soc. Edinburgh relationships of Thomea cannot here be fully 41: 365-383. explored. The ultimate analysis will have to - 1977. Studies in the genus Hypericum L. integrate the findings on wood anatomy. (Guttiferae). I. Infrageneric classification. Bull. Brit. Mus. Nat. Hist., Bot. 5: 293- 355. References Vestal, P.A. 1937. The significance of compara­ Adams, W.P. & N.K.I3. Robson. 1961. A re­ tive anatomy in establishing the relation­ evaluation of the generic status of Ascyrum ship of the Hypericaceae to the Guttiferae and Crookea (Guttiferae). Rhodora 63: and their allies. Philip. 1. Sci. 54: 199-256. 10-16. Wood, C.E. & P. Adams. 1976. The genera of Baas, P. 1970. Floral and vegetative anatomy Guttiferae (Clusiaceae) in the southeastern of Eliaea from Madagascar and Cratoxylum United States. 1. Am. Arbor. 57: 74-90.

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