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 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.