[Palaeontology, Vol. 54, Part 2, 2011, pp. 287–302] CALLISTOPHYTALEAN PTERIDOSPERMS FROM PERMIAN AGED FLORAS OF CHINA by LEYLA J. SEYFULLAH and JASON HILTON School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK; e-mails [email protected]; [email protected] Typescript received 22 September 2009; accepted in revised form 5 April 2010 Abstract: Recent investigations into Permian aged floras Permian period in both North and South China, including from China have highlighted the widespread occurrence of the Upper Shihhotse Formation, Shihchienfeng Group, callistophytalean pteridosperms that challenge previous Xuanwei Formation, and possibly also in the mid-Pennsylva- understanding of their spatial and temporal distribution and nian Benxi Formation. Although macrofossil specimens are diversity. In China, the group spans the Permian period and uncommon elements in the assemblages that contain them, constitutes a distinctive but rare component in many peat- they demonstrate the continuity of callistophytalean pterido- forming environments. The stratigraphically earliest calli- sperms from the Pennsylvanian sub-period into the early stophytalean occurs in the Asselian-Sakmarian stages with Guadalupian epoch of the Permian in North China and into fossils from the Taiyuan Formation of northern China the Lopingian epoch of the Permian in South China. Of the including ovules of Callospermarion undulatum in coal ball species present, both Callistophyton boyssetii and Callosper- assemblages, and ovulate fronds of Norinosperma shanxiensis marion undulatum are known from the Pennsylvanian–earli- and synangiate fronds of Norinotheca shanxiensis in adpres- est Permian age floras of Euramerica, whereas Norinosperma, sion assemblages. More abundant in the fossil records are ad- Norinotheca and Emplectopteris appear to represent endemic pression remains from the Roadian-Wordian stages with the Cathaysian elements. Results imply that callistophytalean Lower Shihhotse Formation preserving abundant vegetative pteridosperms can no longer be excluded from theories of and ovulate remains of Emplectopteris triangularis that is now post-Carboniferous plant evolution and floristics, appearing considered to represent a callistophytalean. The youngest to have played an important role in both Permian and Car- callistophytalean recognised is from the Wuchaipingian- boniferous aged plant communities. The presence of Vesicas- Changhsingian stages with the Xuanwei Formation of pora in several formations from which macro-remains have southern China containing a single stem of Callistophyton not been identified is a hopeful indicator that further calli- boyssetii that provides indisputable evidence of the group in stophytalean pteridosperms are yet to be found. the lead up to the end-Permian mass extinction. These accounts are augmented by analysis of pollen records that Key words: Cathaysian flora, seed plant, pteridosperm, Cal- demonstrate the callistophytalean pollen genus Vesicaspora to listophyton, Callospermarion, Emplectopteris, Norinosperma, be widespread through palynological assemblages from the Norinotheca, Vesicaspora, extinction. T he seed plant order Callistophytales is a rare but (Rothwell 1980, 1981). The C. poroxyloides plant occurs important group of Palaeozoic pteridosperms that lived only in the Pennsylvanian sub-period of North America in peat-forming mire settings and had scrambling ⁄ climb- but the C. boyssetii plant is known from the Pennsylva- ing habits (Rothwell 1981; DiMichele et al. 2006). They nian of North America and earliest Permian of France constitute the most comprehensively characterised pteri- (Rothwell 1975; Galtier 2008). Both whole plant species dosperm order following a series of detailed investigations comprise stems of Callistophyton Delevoryas and Morgan conducted by Rothwell based on anatomically preserved (1954), ovules of Callospermarion Eggert and Delevoryas specimens in coal balls from the Carboniferous system in (1960), pollen organs of Idanothekion Millay and Eggert North America and chert assemblages from the earliest (1970) containing Vesicaspora-type pollen, with the two Permian system of France (Rothwell 1971, 1972a, b, 1975, whole plants having organs attributable to the same genus 1977, 1980, 1981). From this work, two conceptual whole but as distinct species based on details of their morphol- plant species have now been reconstructed, namely, the ogy and histology (Rothwell 1981). In addition to two Callistophyton poroxyloides plant and the C. boyssetii plant reconstructed whole plant species, other species have been ª The Palaeontological Association doi: 10.1111/j.1475-4983.2010.01025.x 287 288 PALAEONTOLOGY, VOLUME 54 assigned to the group including permineralised stems of 1975, 1981). The vascular cambium is bifacial and pro- Johnhallia lacunosa Stidd and Phillips (1982) from Penn- duced a cylinder of xylem and phloem, with periderm sylvanian coal balls of North America (Stidd and Phillips replacing the primary cortex at proximal levels in rela- 1982; DiMichele et al. 2006) and adpression foliage refer- tively old stems (Rothwell 1975, 1981). Callistophyton able to Dicksonites (Schlotheim ex Sternberg) Stertzel and poroxyloides has mesarch vascular bundles and capitate Pseudomariopteris busquetti (Danze´-Corsin) Krings and glands at the margin of the primary cortex differentiating Kerp from the Pennsylvanian sedimentary sequences of it from C. boyssetii that is exarch and has cortical append- Europe (e.g. Rothwell 1981; Krings et al. 2001; Galtier ages that are spine-like (Rothwell 1975, 1981). and Bethoux 2002). Stidd and Phillips (1982) considered In addition to being the most comprehensively recon- Johnhallia to represent a primitive member of the Callist- structed whole plant pteridosperm order that allows fea- ophytales, while Rothwell (1981) and Galtier and Bethoux tures of habit and ecology to be determined (Rothwell (2002) considered Dicksonites pluckenetii to represent the 1981; DiMichele et al. 2006), Callistophytales provide adpression foliage of the Callistophyton plant. Data from valuable information on the reproductive biology of pteri- morphology of Dicksonites suggest the frond had a basal dosperms, including pioneering discoveries on ovule dichotomy although this feature has not yet been verified ontogeny (Rothwell 1971), the oldest evidence of pollen from anatomical information. Evidence from the adpres- tubes (Rothwell 1972a) and pollination drops to facilitate sion record of Dicksonites suggests the presence of two pollination (Rothwell 1977). These studies have led to types that may be distinct species in their own rights, Callistophytales being considered the most reproductively based primarily on differences in the organisation of the sophisticated Palaeozoic pteridosperms (e.g. Rothwell seed-bearing pinnae (Meyen and Lemoigne 1986); while 1980, 1981), pushing back previously interpreted ‘mod- both kinds have fronds with a proximal dichotomy, older ern’ pollination strategies into the Carboniferous period. (Westphalian regional substage; upper Bashkirian to In terms of their evolutionary and phylogenetic impor- upper Moscovian stage) specimens have unmodified tance, they have been included in numerous cladistic fronds with ovules borne subapically on veins in the analyses as the terminal taxon Callistophyton. Cladistic pinnules, whereas in slightly younger (Stephanian regional results demonstrate Callistophyton to diverge from the substage; late Moscovian to Gzhelian stage) fertile fronds, stem after hydrasperman and medullosan pteridosperms ovules are attached subapically to strongly modified pinn- and prior to other, more derived, pteridosperm groups ules. However, it is uncertain whether the two kinds of and cycads (e.g. Rothwell and Serbet 1994; Doyle 2006; Dicksonites relate to the two whole plant species charac- Hilton and Bateman 2006). This position places Callisto- terised from anatomical data, or, whether they represent phyton at an important junction in seed plant evolution phenotypic variation within a single anatomical whole within pteridosperms but may also be of relevance to the plant species (Seyfullah and Hilton 2009: Seyfullah et al. origin of modern seed plant groups including cycads and 2009). Ginkgo. However, in these cladistic results Callistophyton As currently characterised, whole plant species of Cal- is proceeded by, and followed by, evolutionary long listophyton have been reconstructed as small, shrubby branches suggestive of missing taxa or saltational macro- plants with scrambling stems up to 30 mm in diameter evolution (e.g. Bateman and DiMichele 1994; Hilton and (Rothwell 1981). Fronds are small and rarely exceed Bateman 2006; Cleal et al. 2009). 300 mm long and are bipinnately quadrapinnately com- Based on data from North America and Europe, Cal- pound with sphenopterid pinnules (Rothwell 1975, 1981). listophytales first occurred in the middle of the Pennsyl- Branching is axillary with buds or branches borne in the vanian subsystem of the Carboniferous (Rothwell 1981), axils of leaves (Rothwell 1975, 1981). Roots are adventi- but experience a regional demise broadly coinciding with tious and diarch and diverge from the stem distally from the Carboniferous ⁄ Permian boundary (Rothwell 1981) axillary branches where the stem is in close proximity to and have their youngest occurrences in the earliest Perm- ground (Rothwell 1975, 1981). Reproductive organs are ian period