Review of Palaeobotany and Palynology 114 2001) 157±174 www.elsevier.nl/locate/revpalbo

A new species of vascular plants from the Xujiachong Formation Lower Devonian) of Yunnan Province, China

De-Ming Wang, Shou-Gang Hao*

Department of Geology, Peking University, Beijing 100871, PR China Received 31 May 2000; accepted for publication 6 December 2000

Abstract A new species of early land vascular plants, Huia gracilis, is described from the Lower Devonian Pragian±early Emsian) Xujiachong Formation, Qujing district, Yunnan Province, southwestern China. The plant possesses K- or H-type branching in the rhizome and a dichotomously branched erect system. An axillary tubercle is sometimes present at the branching position. Fertile axes terminate in loose spikes comprising terminal and lateral sporangia arranged helically. Sporangia with long stalks are ovate or elongate±ovate and re¯ex adaxially. The sporangium dehisces longitudinally in the radial plane of the fertile axis into two parts. The xylem is probably centrarch. Tracheids of G-type are characterised by annular secondary thickenings, between which is a sheet with irregular simple perforations. There may be some `pores' in the enclosing wall of the perforation. H. gracilis differs from the type species H. recurvata mainly in the branching pattern, more slender morphology of the stem, sporangium and stalk. It is suggested that Huia may have originated from the primitive Cooksonia-like plants. q 2001 Elsevier Science B.V. All rights reserved.

Keywords: Huia gracilis ; Xujiachong Formation; Lower Devonian; China; Fossil plant

1. Introduction recurvata was ®rst described by Geng 1985) from the Posongchong Formation, near Zhichang village, Gumu Four plants have been documented from the Lower county, Wenshan district of Yunnan. Characters of its Devonian Pragian±early Emsian) Xujiachong Forma- branching, sporangium and anatomy were provided. The tion and the corresponding Longhuashan Formation, in new species of Huia described here was found in the Qujing district, Yunnan Province, China. These are middle part of the Xujiachong Formation and its diag- Zosterophyllum yunnanicum HsuÈ, 1966; Cai and nosis is based on more than 60 specimens. Schweitzer, 1983; Hao, 1985), HsuÈa robusta Li, 1982, 1992), Z. australianumHao, 1992) and Drepanophycus 2. Locality and stratigraphy qujingensis Li and Edwards, 1995). In contrast, there are many species from the Lower Devonian Pragian) All specimens were collected from the Xujiachong Posongchong Formation, outcropping in southeastern Formation near Xujiachong village, 13 km northwest Yunnan Province Hao and Gensel, 2001). Huia of Qujing City, in the northeastern part of Yunnan Province and 167 km northeast of Kunming City. * Corresponding author. Details of the locality and stratigraphy are given in E-mail address: [email protected] S.-G. Hao). Hao 1992).

0034-6667/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S0034-666701)00041-0 158 D.-M. Wang, S.-G. Hao / Review of Palaeobotany and Palynology 114 42001) 157±174 According to the lithostratigraphic classi®cation mudstone of yellow-grey colour. The bed containing made by Li and Cai 1978), the Xujiachong Formation the plant is ca. 30 cm thick. incorporates eight lithological units and attains a Specimens were prepared using steel needles. thickness of 869.5 m. The Longhuashan Formation, Conventional hydrochloric followed by hydro¯uoric outcropping ca. 6 km northeast of the Xujiachong acid maceration failed to yield cuticles from axes or Formation, is comparable in lithology and plants sporangia, but spores and tracheids were obtained. with the eighth and upper part of the seventh Slivers of coali®ed axes, when removed and treated unit of the Xujiachong Formation. In the opinion of with concentrated nitric acid or Schulze's solution Fang et al. 1985), however, the Xujiachong Forma- produced satisfactory casts of epidermis and even tion is only 325.8 m thick with a basal conglomerate lumina. These casts were mounted directly on stubs layer. for SEMexamination. For further anatomical investi- As to the age of the Xujiachong Formation, in view gation, extremely rare and ¯at pieces of permineral- of vertebrates, spores and plants, historically there are ised axes less than 1 mm long were embedded and two different opinions. One is that the Xujiachong then sectioned, polished. Only one transverse section Formation is Emsian e.g. Liao et al., 1978; Lu and of a xylem strand was obtained Plate IV, 1). It was Ouyang, 1976; Li and Cai, 1977, 1978). The other is photographed using re¯ected light. that it is of Pragian to Emsian age e.g. Pan et al., 1978; Gao, 1981; Hao, 1992). Recent evidences support the latter opinion. 4. Systematics The Xujiachong Formation is conformably underlain Taking account of the new observations on the by the Guijiatun Formation and unconformably overlain morphology and anatomy, it is possible to expand by the Chuandong Formation. Wang 1997) and Cai the generic diagnosis of Huia. Additions are indicated 2000) suggested that the Guijiatun Formation was by bold typeface. Lochkovian±Pragian age. Zhu and Wang 1996) concluded that the Chuandong Formation was late Division Tracheophyta sensu Kenrick and Crane, Emsian and had a short period of interruption of sedi- 1997) mentation with the Xujiachong Formation. Thus, in incertae sedis view of the biostratigraphy, the Xujiachong Formation is Pragian±early Emsian. In the upper part of this forma- Genus Huia Geng, 1985 tion, Emsian bivalves such as Cimitaria guangxiensis, Antactinodion cf. cuneatum Cai et al., 1994) were Generic diagnosis: Axes naked. Creeping axes with found. The occurrence of ®sh Gantarostrataspis gengi K- or H-type branching. Aerial axes mainly Zhu et al., 1994) here perhaps indicates the successive dichotomous and pseudomonopodial, forming three- evolution of some Pragian elements. With regard to the dimensional systems. Spikes terminal, each compris- plants, those in the mid±lower part of the Xujiachong ing lateral and terminal sporangia. Sporangia with Formation, e.g. Zosterophyllum australianum Hao, long stalks, ovate to elongate±ovate, adaxially re¯exed 1992), Huia and others under study), also occurred and helically arranged. In radial plane of the fertile in the Posongchong Formation Li and Cai, 1977; axis, sporangium dehiscing longitudinally into two Geng, 1985; Hao, 1989; Hao and Gensel, 1998). So, parts. Protostele centrarch, comprising G-type trac- according to the animals and plants, the mid±lower heids with rounded or oval simple perforations and upper parts of the Xujiachong Formation perhaps between annular secondary thickenings. Elongate separately date Pragian and early Emsian. epidermal cells with tapering or truncated ends, stomata anomocytic. Isoporous. 3. Materials and methods Huia gracilis Wang and Hao, sp. nov. Plates I±V; Figs. 1±4; Table 1) The plant is preserved as impressions and compres- sions in a somewhat oxidised micaceous arenaceous Holotype: CPUW 981207 Plate I, 5). D.-M. Wang, S.-G. Hao / Review of Palaeobotany and Palynology 114 42001) 157±174 159 Paratypes: CPUW 981201, 04±06, 09, 10, 13, 15, 5. Description 33, 42, 50, 51. Repository: The Department of Geology, Peking Also see diagnosis of Huia gracilis. University, Beijing, P.R. China. Type locality: Unmade road between Xujiachong and 5.1. Axes and branches Xichong villages, ca. 1000 m north Xujiachong Axes are smooth. Creeping ones divide repeatedly village, Qujing district, Yunnan Province, P.R. up to six times Plate I, 10). Most show K- or H-type China. branching Plate I, 10; Plate II, 4, 5), some with taper- Horizon: Xujiachong Formation, Lower Devonian ing or rounded tips Plate I, 10; Plate II, 4). Plate II, 4 Pragian±early Emsian). shows a K-type branching possibly in early stage of Etymology: Name derived from Latin gracilis, mean- growth. In one instance a creeping axis is 13.1 cm ing slender. long, with a small branching on one side and a Diagnosis: Vascular plant with smooth axes. bifurcation on left Plate I, 8). Creeping axes 1.0±3.1)±6.0 mm wide, K- or H-type The possible sterile axis reaches 21.0 cm long. In branching at angles of 15±1508. three dimensions, it divides in close succession Plate II, 9, 10; Plate III, 1), at angles of 15±608. It shows a Erect axes 0.8±4.5)±8.6 mm wide. The possible trifurcating pattern. The longest single fertile axis is sterile axes dividing at angles of 15±608, sometimes 15.0 cm Plate I, 2). Sometimes ¯exuous Plate II, 1, in close succession forming a trifurcating pattern. 2, 7), fertile axes divide isotomously Plate I, 1, 7) or Occasionally an axillary tubercle occurs at the branch- anisotomously Plate II, 1). A fertile axis divides ing position of fertile or sterile axes. twice with an interval of 4.3 cm Plate I, 7). Fertile axis isotomous or anisotomous at angles of An axillary tubercle is sometimes present at the 10±358, terminating in loose spikes, 4.1±6.6)± branching position of an axis Plate I, 1 at lower 10.0 cm long by 0.5±1.1)±1.6 cm wide. Two or arrow, 7 at upper arrow; Plate II, 9 at arrow, 10 at three terminal and many lateral sporangia in a lower arrow). It has rounded margin and measures complete spike. Vertical distance between sporangial 2.0±4.8 mm high by 2.3±4.0 mm wide. Some lateral insertion 1.9±5.0)±12.0 mm. Sporangia 1.9±4.7)± axes of the possible sterile branches end in rounded 7.5 mm high by 1.0±3.3)±5.2 mm wide n ˆ 200). tips Plate II, 10, upper arrow; Plate III, 1), 3.9± Parallel-sided stalks, 4.0±8.7)±13.0 mm long by 5.5 mm high by 2.2±3.6 mm wide. Plate II, 9±11 0.2±0.9)±2.0 mm wide, inserted at angles of 12± may be suggestive of sterile branches. An axis 658 n ˆ 97). Plate II, 8) shows a central dark line ca. 1.0 mm Protoxylem 5±10 mm and metaxylem 10±30 mmin wide 16% of the axis diameter), representing the diameter. Secondary thickenings 1.5±2.2)±3.1 mm vascular tissue. thick, with vertical distance of 1.6±3.7)±6.2 mm. Secondary wall between thickenings bearing 5.2. Spikes and sporangia irregular simple perforations, circular or oval, 0.1± 0.7)±1.4 mm in diameter. Sometimes small `pores', The helically borne sporangia form terminal spikes 0.1±0.5 mm in diameter, in the enclosing wall of Plate I, 1, 2, 5, 7, 8; Plate II, 1, 2, 7; Fig. 1A, B). A perforation. complete spike has two or three terminal sporangia Elongate epidermal cells parallel to the main axis. Plate I, 5; Plate II, 6; Plate III, 2, 3; Fig. 1A, G) Longer cells 230±296)±400 mm long by 12±22)± and many lateral sporangia. Upper sporangia in a 35 mm wide, 9±29 times longer than wide. Shorter spike sometimes are a little more closely spaced ones 77±134)±325 mm long by 15±28)±40 mm Plate I, 2, 5; Plate II, 7). Sporangium size tends to wide, 2±11 times longer than wide. Elongate stomata decrease distally Plate II, 1, 7), but this is not always 48.0±66.0 mm long by 21.0±27.0 mm wide. the case Plate I, 2, 5). Preparation reveals up to 21 Isospores rounded triangular, trilete and 22±41)± sporangia per spike Plate I, 5; Fig. 1A). 68 mm in diameter. Radiate rays extending 2/3±1 Sporangia are ovate or elongate±ovate in adaxial along the spore radius. Exine 1.0±2.0 mm thick. Plate III, 4, 5, 12) and in side view Plate II, 3; Plate 160 D.-M. Wang, S.-G. Hao / Review of Palaeobotany and Palynology 114 42001) 157±174 D.-M. Wang, S.-G. Hao / Review of Palaeobotany and Palynology 114 42001) 157±174 161 III, 8, 10). They re¯ex adaxially Plate I, 9; Plate III, 8; only primary xylem. As shown in Plate IV, 1, the Fig. 1F, J K), thus could be more effectively protected. elliptical xylem strand was ¯attened during fossilisa- In a few cases, a longitudinal dehiscence line, 0.1± tion to form strap shape, 0.6±1.2 mm long by 0.2± 0.2 mm wide, is visible in adaxial view Plate III, 4, 1.0 mm wide. The probable protoxylem area is 5, 12; Fig. 2E±G). Usually there is no clear demarcation indicated by an arrow. The extra-xylary tissues have between the sporangium and stalk except for a few undergone considerable decay during fossilisation. examples Plate I, 9; Plate III, 8, 11; Fig. 1F, J, K; Limonitic in®lls of tracheid lumina lumen casts) Fig. 2D, arrow). Therefore the dehiscence line often are visible Plate IV, 1±3). The tracheids are round seems to be fused by the subtending stalk. In abaxial or polygonal, 5±15)±30 mm in diameter. The cell wall view a sporangium appears to have two longitudinal Plate IV, 3) has annular secondary thickenings Plate parts Plate III, 6, 7; Fig. 2B, C). So it is likely that, IV, 2, upper arrow) and perforation cast is visible Plate in the radial plane of the fertile axis, the sporangium IV, 2, lower arrow). The outer cells are 10±30 mmin splits longitudinally into two parts. diameter and the central ones are 5±10 mm across. Thus Sometimes, the stalk turns abaxially Plate II, 7; the xylem maturation is probably centrarch. Plate III, 10; Fig. 1H, I), which could possible be The tracheids are indirectly attached annular due to the preservation. Occasionally the stalk elements sensu Bierhorst, 1960). In longitudinal thickens where it contacts the lower part of the view the protoxylem elements were not identi®ed re¯exed sporangium Plate III, 10, 12, arrows; Fig. with certainty. The tracheids measure more than 1E, H, I, arrows; Fig. 2E, arrow), which perhaps 2750 mm long and taper distally Plate IV, 12, acts as a sporangial `pedicile'. Two stalks sometimes arrow). Where the cell wall has broken away, the attach adjacently to the axis Plate I, 6, arrow; Plate II, lumen cast negative cast, sensu Li, 1990) is exposed 1, arrow; Fig. 1D, E). In many cases, the stalks are the with the horizontal indentations Plate IV, 4, 6, 7, 9, same in width to or merge decurrently with the axes 10, 12). These indentations represent the position of on which they occur Plate I, 1, 3±5; Plate II, 1, 2, 7; the original annular secondary thickenings Fig. 3). Plate III, 10) and seem to represent degenerate lateral Fragments of these thickenings could be left in the fertile axes. A reconstruction illustrating the general indentations Plate IV, 4 at left arrow, 6, 9 at morphology of the plant is shown in Fig. 4. arrow). In macerated tracheids, the annular secondary thickenings are smooth Plate IV, 5, 11). They some- 5.3. Anatomy times bifurcate Plate IV, 4, 10). The ratio of interval between annular thickenings to the width of metaxy- In transverse section the preserved protostele shows lem tracheids is 0.3.

PLATE I. Huia gracilis, sp. nov. 1. An isotomous fertile axis. Lower arrow indicates an axillary tubercle on the lateral branch; upper arrow, a sporangium enlarged in Plate III, 4. CPUW 981201  £ 1.3). 2. Two fertile axes with loose spikes. CPUW 981204  £ 0.8). 3. A fertile axis showing the helical arrangement of sporangia. Arrows indicate sporangia separately enlarged in Plate III, 5, 11. CPUW 981250  £ 1.5). 4. Two fertile axes. CPUW 981226  £ 1.6). 5. Holotype. Two fertile axes. Right one shows a complete spike, note the helical sporangial arrangement and terminal sporangia. CPUW 981207  £ 1.2). 6. A fertile axis. Arrow indicates two sporangia in abaxial view, with adjacent stalks. CPUW 981235  £ 1.5). 7. A twice-branching fertile axis on left and fragments of spikes on right. Arrows indicate two branching points, note the axillary tubercle upper arrow). CPUW 981206  £ 1.1). 8. Creeping and fertile axes. The right spike is the counterpart of that in Plate II, 7. Arrow indicates the dichotomy of a creeping axis. CPUW 981211  £ 0.8). 9. Two re¯exed sporangia in side view. CPUW 981227  £ 1.5). 10. A creeping axis showing K- or H-type branchings. CPUW 981210  £ 0.9). 162 D.-M. Wang, S.-G. Hao / Review of Palaeobotany and Palynology 114 42001) 157±174 In face Plate IV, 4 at arrow L, 9) and sectional casts just connect with but do not penetrate through Plate IV, 10) view of the tracheids etched with it. Thus, this outer layer may have been preserved as a Schulze's solution, a continuous outer layer neither thin cast, representing the original position of the cell protrudes into the indentations nor joins the secondary wall. thickenings preserved in them, it just crosses them. In Seen from the inside Plate IV, 5, 8, 11) or outside addition this outer layer is smooth, the perforation Plate IV, 8, uppermost part) of the macerated D.-M. Wang, S.-G. Hao / Review of Palaeobotany and Palynology 114 42001) 157±174 163 tracheid, the secondary wall is perforated. The per- Kenrick and Crane, 1991). In addition, the cell wall forate layer is between and continuous with the bars measurements are: thickness of annular thickening of secondary thickenings. The irregular simple d ˆ 1.5±2.2)±3.1 mm; interthickening distance perforations seem to have borders ca. 0.2 mm wide, e ˆ 1.6±3.7)±6.2 mm; maximum lumen diameter sometimes fused together) facing the tracheid lumen W ˆ 30.0 mm; thickenings number per mm N Plate IV, 11, arrow; Fig. 3A). In the enclosing wall of mm21 ˆ 110±155)±220; and interbar perforation a perforation there sometimes are several small diameter 0.1±0.7)±1.4 mm. The d and e of H. recur- `pores' Plate IV, 5, 11, arrows; Fig. 3A). The perfora- vata, respectively, are 2.5 and 3±6.5 mm Geng, tions are ®lled with mineral and form casts Plate IV, 1985). All of them approach the measurements of 6, 9, 10; Fig. 3B), ca. 0.7 mm long by 0.3 mm wide. G-type cells Kenrick and Crane, 1991; Kenrick et The perforation casts of adjacent cells do not coincide al., 1991). Plate IV, 6). In many cases, these casts taper toward the cell wall Plate IV, 6, arrows; Fig. 3B). Accord- 5.4. Epidermal cells ingly, the perforation has wider aperture. Correspond- ing to the perforation border, the perforation cast has a All are casts of the inner surface of epidermis. rim where it connects with the lumen cast Plate IV, 6, Epidermal cells with tapering or truncated ends have arrows; Fig. 3B). Some of the perforation casts bear long axes parallel to the main stem. There are the smaller super®cial `tubercles' Plate IV, 6, lower longer cells Plate V, 1, 5, 6). Those located near arrow; Fig. 3B), which are counterpart of the `pores' branches or around the possible papillate bases in the perforation. In transverse or sectional view, the Plate V, 7±9) are shorter and show variation in perforation casts seem to cross the original ligni®ed pro®le. The polygonal cells in Plate V, 9 are covered layer of secondary wall Kenrick and Edwards, 1988a, by numerous microcrystals ca. 5.0 mm in diameter, Fig. 26C; this paper, Fig. 3) to connect with the outer which resemble the microcrystalline pyrites respon- cell wall Plate IV, 2 at lower arrow, 10 at lower-left sible for depressions on the cuticle surface of Gosslin- arrows). The width of these casts corresponds to the gia breconensis Kenrick and Edwards, 1988a, Fig. minimum of perforation diameter, the length of them 24). In only one example, elongate stomata are perhaps represents the thickness of the ligni®ed preserved Plate V, 1, arrows). They are anomocytic, secondary wall. each comprising two elongate guard cells surrounding Thus in H. gracilis, the inner wall of the conducting a pore Plate V, 2±4, arrow g, p). The long axes of cell the ligni®ed layer) has irregular simple perfora- stomata are parallel to the surrounding epidermal tions between annular thickenings, which typi®es the cells. Each stoma is enclosed by ca. six epidermal G-type tracheids Kenrick and Edwards, 1988a; cells. The stomatal density is ca.13 mm22. There is

PLATE II. Huia gracilis, sp. nov. 1. A ¯exuous fertile axis dividing anisotomously. Arrow indicates two sporangia with adjacent stalks, respectively in abaxial view and in side view. CPUW 981233  £ 1.1). 2. Two ¯exuous fertile axes. CPUW 981203  £ 1.2). 3. A small immature sporangium near a spike top. CPUW 981245  £ 11.0). 4. A K-type branching with blunt tips. CPUW 981238  £ 1.7). 5. A creeping axis with repeated branchings extending toward different directions. CPUW 981205  £ 0.8). 6. A spike showing closer arrangement of terminal sporangia. CPUW 981218  £ 1.4). 7. A ¯exuous fertile axis showing loose arrangement of sporangia. Arrow indicates a possible branching point. CPUW 981209  £ 1.1). 8. A piece of axis containing the middle carbonaceous strand. CPUW 981220  £ 1.6). 9. A possible sterile axis dividing in close succession, showing trifurcating pattern. Arrow indicates an axillary tubercle on the lateral branch. CPUW 981213  £ 0.8). 10. The same as in 9. Lower arrow indicates a tubercle a little above the branching point and upper arrow, a rounded tip. CPUW 981215  £ 1.1). 11. A possible sterile axis with repeated branchings. CPUW 981212  £ 1.3). 164 D.-M. Wang, S.-G. Hao / Review of Palaeobotany and Palynology 114 42001) 157±174 D.-M. Wang, S.-G. Hao / Review of Palaeobotany and Palynology 114 42001) 157±174 165 a possible papillate base Plate V, 7, arrow), possible centrarch protostele. Adding to the anatomi- 160 £ 94 mm in diameter, picked directly from the cal description of H. recurvata, Li and Cui 1995) had lower tip of the lateral branch in Plate II, 4. illustrated clear centrarch xylem. H. gracilis differs The sporangial cells Plate V, 10) are elongate, 50± from H. recurvata in several aspects, i.e. axis, spike 69)±90 mm long by 20±24)±30 mm wide. No and sporangium Table 1). The major differences lie stomata were observed. This piece of material was in the branching pattern and dimension of axis, spor- picked off the counterpart of a sporangium in angium and sporangial stalk. The axes of H. recurvata Plate I, 3. divide mainly pseudomonopodially. In H. gracilis the fertile axes are chie¯y isotomous. Although more 5.5. Spores slender in gross morphology, its mature spikes bear more sporangia than H. recurvata. We exclude the possi- Isospores were observed with both light micro- bility that ontogenetically H. gracilis represents the scope LM) Plate III, 9, 13, 16) and scanning electron juvenile stage of H. recurvata, because the former microscope SEM) Plate III, 14, 15). The trilete rays plant is based on quite extensive specimens with spikes Plate III, 9, 13, 15, 16) extend 2/3±1 along the spore and the immature sporangium is different in form e.g. radius. Under LMthe spore seems granular, but Plate II, 3). So, H. gracilis is designated as a new species. ornament detail is impossible to elucidate. Spores The ovate, adaxially re¯exed sporangium makes Huia observed with SEMexhibit the reticulate ornament, different from other early land plants. Taeniocrada 0.2±1.1 mm in diameter. This reticulate nature is decheniana has oval sporangia in groups, the subtending perhaps a taphonomic effect, resulting from decay or stalk is fused to one side of the anatropous sporangium pyrite crystal damage. KraÈusel and Weyland, 1930; Schweitzer, 1980). It is somewhat comparable with Huia, but the sporangial 6. Comparison dehiscence and anatomy are unknown. Furthermore it has consistently distinctive ribbon-like axes with This plant is clearly a Huia in that it possesses repeated dichotomies and circinate tips. Sporangia are smooth axes, bifurcate fertile branching, terminal mostly terminal. In contrast Huia has terete axes, dicho- spikes of lateral and helical sporangia, ovate and tomous or pseudomonopodial branching, lateral sporan- long-stalked sporangia re¯exing adaxially, and a gia on long stalks and lacks circinate tips.

PLATE III. Huia gracilis, sp. nov. 1. A possible sterile axis having lateral branches terminating in rounded tips. CPUW 981251  £ 1.8). 2. Terminal sporangia of a spike. Arrow indicates a sporangium obscured by the left one. CPUW 981234  £ 4.3). 3. Counterpart of 2. CPUW 981225  £ 1.9). 4, 5. Sporangia from Plate I, 1, 3 upper arrows), in adaxial view, show the longitudinal dehiscent line. The sporangial stalk in 5 was uncovered. CPUW 981201, -50  £ 7.0, £ 7.7). 6, 7. The abaxial view of sporangia showing two possible parts and stalk. CPUW 981229, -52  £ 11.0, £ 12.3). 8. A re¯exed sporangium in side view, upper two arrows indicate the demarcation between the sporangium and stalk; lower arrow, stalk- inserted axis. CPUW 981258  £ 10.0). 9. LMof a spore showing the trilete rays with darkened area. WH1-20  £ 550). 10. A sporangium turning abaxially, in side view, shows the clear stalk thickening arrow). CPUW 981244  £ 5.6). 11. A sporangium from Plate I, 3 lower arrows), in side view. Arrow indicates the possible demarcation between the sporangium and stalk. CPUW 981250  £ 5.9). 12. A sporangium from the counterpart of Plate I, 3, in adaxial view, showing the longitudinal dehiscent line. Arrow indicates the stalk thickening. CPUW 981242  £ 5.4). 13. LMof two spores, the left one showing trilete rays. WH1-17  £ 880). 14. SEMof a spore showing reticulate surface and microcrystals. WH7-21  £ 3520). 15. SEMof a spore showing trilete rays and reticulate surface. WH-03  £ 1610). 16. LMof a spore showing trilete rays. WH1-19  £ 880). 166 D.-M. Wang, S.-G. Hao / Review of Palaeobotany and Palynology 114 42001) 157±174 D.-M. Wang, S.-G. Hao / Review of Palaeobotany and Palynology 114 42001) 157±174 167 Besides T. decheniana and Huia, Nothia aphylla subaxillary one does. This difference may result El-Saadawy and Lacey, 1979) has recurved sporan- from the preservation. Besides Huia gracilis, there gia. As in Huia, the axes of N. aphylla dichotomise, are also axillary or subaxillary tubercles mainly the lateral and terminal sporangia form terminal in plants with lateral sporangia, e.g. Gosslingia spikes. The xylem is centrarch. However it differs breconensis Edwards, 1970) and Odonax borealis from Huia in the reniform sporangium dehiscing Gerrienne, 1996). These tubercles differ in position transversely, shorter stalk and branches occurring from the axial tubercle, root-like and rhizophore-like within the fertile zone. branches of HsuÈa robusta, which are 4.5±9.0 mm Huia was though to resemble the sporangial region above the branching point and on the main axis Li, of Hicklingia Banks, 1992). It also shows similarity 1982). The axillary tubercle of H. gracilis sometimes in the stalk thickening in junction with the sporangium occurs a little above the branching point but on the and single sporangium below the branching point, but lateral axis Plate II, 10, arrow).The axillary tubercle lacks the upright sporangia of Hicklingia edwardii, of the possible sterile axis perhaps represents future which are hemispherical to globose Edwards, lateral branchings, as is illustrated by the successive 1976). In the latter plant, double lines extend developmental stages Plate II, 9±11). The tubercle vertically across the sporangium possibly resulting development of the fertile branching e.g. Plate I, 1, in a smaller adaxial valve and a larger abaxial valve. 7) is unclear in view of the increased number of fertile dichotomies. The axillary or subaxillary tubercle is interpreted as 7. Discussion the base of a lateral branch e.g. G. breconensis, Edwards, 1970) or a rhizophore as in Selaginella 7.1. Axillary tubercles e.g. Crenaticaulis verruculosus, Banks and Davis, 1969). Kenrick and Crane 1997, pp. 153±154) In Huia gracilis the tubercle seems not to occur just suggested that the subordinate branch was stemlike below the branching point, as the real axillary or rather than a rhizophore, provisionally homologous

PLATE IV. Huia gracilis, sp. nov. All the photographs except 1 are SEMs. 1. Transverse section of a ¯attened axis showing the possible centrarch xylem strand. Arrow indicates the small tracheids area of protoxylem. Note the outside large tracheids of metaxylem and crack in the strand. WH3-06  £ 98). 2, 3. Transverse view of metaxylem tracheids. Note the annular thickening upper arrow) and perforation casts connecting with the cell wall lower arrow) in 2. WH2-01  £ 1200), WH-06  £ 1540). 4. Longitudinal view of tracheids with fragments of cell wall arrow L) and exposed lumen casts. Left arrow indicates the fragment of secondary thickening in the indentation. WH6-03  £ 1290). 5. Longitudinal view of a macerated tracheid showing hollow annular thickenings and irregular simple perforations. Arrows indicate small `pores' in the enclosing wall of perforation. WH-11  £ 4420). 6. Longitudinal view of two tracheids showing different dimension of perforation casts between indentations of secondary thickenings. Arrows indicate perforation casts contracting toward the cell wall and having rims. Note the small `tubercles' on the surface of a cast lower arrow). WH-00  £ 3800). 7. Left tracheids have stripes of cell wall peeled off, revealing longitudinal rows of lumen casts and indentations of secondary thickenings. WH6-06  £ 424). 8. Macerated tracheids showing annular thickenings and perforations. WH-09  £ 1200). 9. Enlargement of the lower-right tracheid in 12. Note the cell wall, perforation casts and secondary thickening in the indentation arrow). WH6-22  £ 2340). 10. Two tracheids showing the perforation casts right arrow) and fragment of cell wall connecting with perforation casts left arrows). WH6-07  £ 1940). 11. Enlargement of the lower-left tracheid in 8, showing the irregular simple perforations between thickenings. Note the perforation bearing border and small `pores' in the enclosing wall arrow). WH7-14  £ 4240). 12. Longitudinal view of a tracheid with the tapering end arrow). WH6-20.  £ 368). 168 D.-M. Wang, S.-G. Hao / Review of Palaeobotany and Palynology 114 42001) 157±174 D.-M. Wang, S.-G. Hao / Review of Palaeobotany and Palynology 114 42001) 157±174 169

Fig. 2. Huia gracilis, sp. nov. A) A terminal immature sporangium Plate II, 3: CPUW 981245). B, C) Sporangia in abaxial view, showing the possible longitudinal two parts and stalk Plate III, 7, 6: CPUW 981252, -29). D) A sporangium in side view, showing possible demarcation between the sporangium and stalk arrow, Plate III, 11: CPUW 981250). E±G) Sporangium in adaxial view, showing longitudinal dehiscent line. Note stalk thickening E, arrow, Plate III, 12, 4, 5: CPUW 981242, -01, -50).

with the structure typical of H. robusta and outgrowth on the lateral branches of Sawdonia ornate Rayner, 1983). These tubercles or branches may be the result Fig. 1. Huia gracilis, sp. nov. A) A complete spike of two or three of the versatility of apical meristems in early land terminal and many lateral sporangia arranged helically Plate I, 5: plants Edwards and Kenrick, 1986; Banks, 1992). CPUW 981207). B) A fertile axis showing relatively loose and helical sporangia Plate I, 2: CPUW 981204). C) A fertile axis showing helical sporangia part and counterpart, Plate I, 3: 7.2. Anatomy CPUW 981250, -42). D, E) Two sporangia with adjacent stalks, note stalk thickening E. arrow, Plate II, 1: CPUW 981228, -33). F) An adaxially re¯exed sporangium with clear demarcation between As suggested by Li and Cui 1995); Kenrick and sporangium and stalk Plate III, 8: CPUW 981258). G) Terminal Crane 1997), the scalariform thickenings of Huia sporangia, note the obscured sporangium arrow. Plate III, 2: recurvata Geng, 1985) are annular ones. The latter CPUW 981234. H, I) Sporangial stalks directing abaxially, note authors also interpreted its wall structure as possible stalk thickening arrow, Plate II, 7; Plate III, 10: CPUW 981209, G-type, which is con®rmed in H. gracilis. In addition, -44). J, K) Re¯exed sporangium Plate I, 9: CPUW 981227). the poorly preserved and uncertain openings of the tracheid wall Geng, 1985) are now clari®ed as original interbar simple perforations in H. gracilis.

PLATE V. Huia gracilis, sp. nov. All photographs except 10 are SEMS of casts of the inner surface of the axes. 1. General view of epidermis cells and stomata arrows), stomata a and b are separately shown in 2, 3. WH6-15  £ 65). 2±4. A stoma showing two guard cells arrow g) enclosing a pore arrow p). WH6-15  £ 416),  £ 320),  £ 380). 5, 6. Outline of epidermal cells with tapering or truncated ends. WH6-12, -19  £ 181). 7, 8. Shorter, pillar-shaped epidermal cells. Arrow in 7 indicates a possible papillate base. WH6-13  £ 106), WH6-14  £ 238). 9. Rectangular or polygonal epidermal cells showing numerous microcrystals. WH-02  £ 328). 10. Cuticle of the sporangium showing the shape of epidermal cells. WH-04  £ 262). 170 D.-M. Wang, S.-G. Hao / Review of Palaeobotany and Palynology 114 42001) 157±174 Bierhorst, 1960; Bierhorst and Zamora, 1965; Brauer, 1980; Taylor, 1986; Cook and Friedman, 1998). In H. gracilis the continuous ligni®ed) part of the second- ary cell wall is the later-formed layer and exists clearly, the discontinuous cellulose) part of the secondary wall is the ®rst-formed layer and has been lost during etching or preservation. As in H. gracilis, the tracheid interbar perforations of Gosslingia breconensis Kenrick and Edwards, 1988a) and Thrinkophyton formosum Kenrick and Edwards, 1988b) are further supported by SEM Fig. 3. Huia gracilis, sp. nov. Longitudinal view of tracheid wall A) observations of counterpart small `blobs' or `knobs' and lumen cast B). A) Annular secondary thickenings and interbar on the surface of lumen casts. These perforations of irregular simple perforations of different size. Dense, light stipples the secondary wall were considered original in struc- respectively represent the ligni®ed, cellulose layer of secondary wall. Cellulose area also includes primary wall. Note small ture, not caused by the mineral growth in that the `pores' in the enclosing wall of perforation. B) Indentations corre- ligni®ed annular thickenings are smooth Kenrick sponding to annular secondary thickenings and perforation casts and Edwards, 1988a; Berry and Edwards, 1994). In with rims, contracting toward the cell wall. Note perforation casts H. gracilis the annular thickenings are smooth and the bearing small `tubercles', counterpart of `pores' in perforations. perforations could be viewed from both interior and exterior of the cell. Perforations and counterpart The ratio of distance between transverse thicken- protrusions are not angular, but circular or oval. The ings to width of tracheid is 0.3, so metaxylem protrusions themselves are parts of the lumen casts elements of H. gracilis may be de®ned as `close-set and do not merely adhere on the lumen casts like annular' Li, 1992), which represents a simple and microcrystals. Furthermore, some protrusions bear primitive type of metaxylem tracheid. small super®cial `tubercles', which is uncharacteristic The two stage deposition of secondary wall has of crystals. Therefore, the protrusions are casts of been reported in living and fossil plants e.g. perforations and `tubercles' could be counterparts of

Table 1 Comparison between Huia recurvata and H. gracilis, sp. nov.

Huia recurvata Huia gracilis

Axis: Width mm) 6.0±14.0 0.8±4.5)±8.6 Erect branching pseudomonopodial isotomous Axillary tubercle no yes Spike: Spike length mm) up to 65 41±66)±100 Spike width mm) up to 18 5±11)±16 Sporangial number per spike 3±9 up to 21 Degree of compact arrangement sporangial number/10 mm) 1.4) E)a 1.4±2.1)±2.7 E)a Sporangium below branching yes no Sporangium: Sporangial height mm) 2.7±7.9)±10.0 1.9±4.7)±7.5 Sporangial width mm) 1.6±4.0)±5.0 1.0±3.3)±5.2 Stalk length mm) 10.0±20.0 4.0±8.7)±13.0 Stalk width mm) 1.5±2.1)±3.0 0.2±0.9)±2.0 Stalk insertion 8) 10±30 12±65

a E, estimated based on the original description). D.-M. Wang, S.-G. Hao / Review of Palaeobotany and Palynology 114 42001) 157±174 171 `pores' in the perforation, the tracheidal perforations and `pores' are original in structure. The tracheid perforation of H. gracilis sometimes seems to have a border as in Drepanophycus gaspianus Grierson and Hueber, 1967) and Barinophyton citrul- liforme Brauer, 1980). Contracting toward the cell wall, the three-dimensional shape of the perforation differs from that of the bordered pit. The `pores' in the enclosing wall of the perforation may act to strengthen the substance exchange through tracheids.

7.3. Phylogenetic position

Considering that Huia recurvata and Taeniocrada decheniana have ovate, anatropous sporangia aggre- gating into spikes or groups, Geng 1985) established the Taeniocradaceae to include only these two species, provisionally assigned to the Rhyniophytina sensu Banks, 1975). In view of the unknown anatomy of T. decheniana and great difference between them see Comparison), it is perhaps early to place them in the same family, merely according to limited sporan- gial similarities. In view of the phylogeny, similar to Renalia Gensel, 1976), Nothia and HsuÈa, Huia may have stemmed from certain primitive plants e.g. Cooksonia-like plants with simple isotomous axes terminating in sporangia, through some intermediates. The possible reasons are: 1) naked axes divide iso- tomously and anisotomously; 2) the spike consists of both terminal and lateral sporangia sometimes two lateral sporangia have adjacent stalks); 3) sporangia have longer stalks possibly derived from lateral fertile branches also see Geng, 1985); and 4) protostele has centrarch xylem although the transverse anatomy of Renalia is unknown). In this process of developing from terminal to lateral sporangia, Renalia, Nothia and Huia seem to be more advanced than HsuÈa, because they bear sporangial stalks other than lateral fertile branches. Among them, the stalk of Huia is comparatively longer. Until details, such as sporangial dehiscence and anatomy, are obtained, Huia recurvata has been considered as incertae sedis Banks, 1992), possible rhyniophytes Gensel, 1992), or bridging zosterophyl- lophytes and trimerophytes Edwards, 1997). Banks Fig. 4. Huia gracilis, sp. nov. Reconstruction of a part of the plant. 1992) also thought it recalled the trimerophytes and differed from the rhyniophytes in view of the robust 172 D.-M. Wang, S.-G. Hao / Review of Palaeobotany and Palynology 114 42001) 157±174 axes branching pseudomonopodially. Huia is also for his loan of the holotype, Professors Cai Chong- dichotomous and differs from the trimerophytes or Yang, Fang Zong-Jie and Zhu Min for their useful Euphyllophytina sensu Kenrick and Crane, 1997) discussions. We are also indebted to Mr Zhou Chun- mainly in its terminal spike of many lateral sporangia Yuan, Xu Jian-Ru, Xue-Jia and Dr Liu Jian-Bo for aid and G-type tracheids. Also, it does not ®t the Rhyniop- in preparing photos and drawings. sida sensu Kenrick and Crane, 1997) mainly because of lacking the S-type tracheids. Although Huia is super®cially more similar to the Lycophytina sensu References Kenrick and Crane, 1997) in the lateral sporangia and G-type tracheids, it is conspicuously different in Banks, H.P., 1975. Reclassi®cation of Psilophyta. Taxon 24 4), possessing ovate, re¯exed sporangia which are long- 401±413. Banks, H.P., 1992. The classi®cation of early land plantsÐ stalked and dehisce longitudinally and centrarch revisited. Geophytology 22, 49±63. xylem. Being a vascular plant, thus it could only be Banks, H.P., Davis, M.R., 1969. Crenaticaulis, a new genus of provisionally treated as incertae sedis in the Tracheo- Devonian plants allied to Zosterophyllum, and its bearing on phyta sensu Kenrick and Crane, 1997). the classi®cation of early land plants. Am. J. Bot. 56 4), G-type tracheid and exarch xylem are typical of the 436±449. Berry, C.M., Edwards, D., 1994. New data on the morphology and Lycophytina consisting of plants characterised by anatomy of the Devonian zosterophyll Serrulacaulis Hueber and lateral sporangia. The exception is that besides Banks from Venezuela. Rev. Palaeobot. Palynol. 81, 141±150. Huia, HsuÈa has G-type cell Kenrick and Crane, Bierhorst, D.W., 1960. Observations on tracheary elements. Phyto- 1997) and centrarch xylem Li, 1982, 1992). The reni- morphology 10, 249±305. form sporangia of the latter plant are terminal but Bierhorst, D.W., Zamora, P.M., 1965. Primary xylem elements and element associations of angiosperms. Am. J. Bot. 52 7), perhaps developing laterally. In addition, Nothia has 657±710. reniform sporangia and central protoxylem, although Brauer, D.F., 1980. Barinophyton citrulliforme Barinophytales typical tracheid thickenings are not observed. Thus, Incertae Sedis, Barinophytaceae) from the Upper Devonian of there is perhaps another group of plants characterised Pennsylvania. Am. J. Bot. 67 8), 1186±1206. by lateral fertile structures and centrarch xylems, Cai, Chong-Yang, 2000. Nonmarine Devonian. In: Stratigraphical Studies in China 1979±1999). University of Science and Tech- which possibly represent a natural taxon. Among nology of China Press, Hefei, pp. 95±127 in Chinese). these plants, however, the lateral fertile structures Cai, Chong-Yang, Schweitzer, H.J., 1983. UÈ ber Zosterophyllum could be somewhat morphologically different, e.g. in yunnanicum HsuÈ aus dem Unterdevon SuÈdchinas. Palaeonto- sporangial shape or dehiscence as shown by Huia and graphica B 185, 1±10. HsuÈa. If we further consider the plant with leaf struc- Cai, Chong-Yang, Fang, Zong-Jie, Li, Xing-Xue, Wang, Yi, Geng, Liang-Yu, Gao, Lian-Da, Wang, Nian-Zhong, Li, Dai-Yun, Liu, ture, e.g. Eophyllophyton Hao, 1988; Hao and Beck, Zhong-Heng, 1994. 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