ephedroids from the Early Cretaceous Yixian Formation in Liaoning ...

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252 C. Rydin et al.: Cretaceous ephedroids from China
C. Rydin et al.: Cretaceous ephedroids from China 253 Considering the nomenclatural problems with the taxon Ephedrites and the difficulty to unambiguously correlate the present material with extant Ephedra, we prefer to keep the name Liaoxia, and suggest that Liaoxia is used for Ephedra-like megafossils that cannot be unambiguously assigned to the extant genus. Interpretation of the new fossils and comparison with extant species. The material presented here comprises impression-compression fossils with remains of oxidized organic material. Most specimens have stems, leaves, and cones in connection, but none of the fossils is preserved as whole plants and none has roots attached. No anatomical details are preserved. Characters are summarised in Table 2. The reconstruction of Liaoxia chenii (Fig. 21) is based on the holotype (PB17800) and the new specimens (PB20717–PB20718). Vegetative characters of Liaoxia. The fossils have erect stems, which are longitudinally striate probably from preserved fibers. Upper parts are thinner than the basal parts and in all species the stems become wider at the nodes. Liaoxia robusta is larger than the other species and has the widest stems, but the variation is generally larger within each plant than between them. Leaves are absent in Liaoxia changii and L. elongata; leaf scars are missing in all specimens. In Liaoxia longibractea, only the uppermost part of a reproductive shoot is preserved and it is unknown whether or not it had leaves. The other species all have narrow, linear leaves, opposite at nodes. The leaf bases are probably sheeted in all the species, but the poor preservation prevents unambiguous conclusions. The venation is also generally poorly preserved, but obvious in at least some parts of the leaves. In all species there is a primary parallel venation and no second order venation. Liaoxia chenii and L. acutiformis appear to have two parallel veins. Liaoxia robusta has four veins. In extant Ephedra, the size and shape of leaves and stems may vary significantly within and between species (Gifford and Foster 1989) and the variation in the fossils is covered in the extant genus. For example, Ephedra leaves are generally minute (less than 10 mm long), ovate to triangular in shape, but Ephedra foliata has linear leaves with a well-developed lamina, often 10–15 mm long, sometimes extending up to 40 mm in length (Freitag and Maier-Stolte 1994). Leaves of Ephedra have 2–3 parallel veins (Kubitzki 1990). Second order venation is unknown in Ephedra, but occurs in Gnetum and Welwitschia. Cones and cone bracts of Liaoxia. The cones of Liaoxia chenii and L. robusta are obovate and wide, whereas the cones of L. acutiformis and L. changii are elongate to slightly obovate. Cones of L. elongata are narrowly elongate, but one of the cones of L. elongata has a distinctly different shape and is smaller and rounded. It was probably preserved in an immature stage. In L. longibractea, the cones are rounded to obovate and several cones are densely crowded at nodes, forming a head-like structure. Multiple axillary branching resulting in four or more cones at a node is obvious in Liaoxia robusta, L. longibractea and L. elongata, and this feature is also common in extant Ephedra. Presence of multiple axillary buds is a synapomorphy for the Gnetales (Crane 1996, Doyle 1996). Liaoxia chenii has 2–6 pairs of ovate to triangular cone bracts with a pointed apex. b Figs. 16–20. Liaoxia robusta Rydin, S.Q. Wu et Friis sp. nov. and Liaoxia longibractea Rydin S.Q. Wu et Friis sp. nov. 16–18 Liaoxia robusta sp. nov (PB20719–PB20720); a large species with preserved seeds, also in the axil of proximal cone bracts. Leaves and stems are surrounded by precipitations that make them appear wider than they are. 19–20 Liaoxia longibractea sp. nov. (PB20725–PB20726); the uppermostpartofareproductiveshoot. It is unknown if this species had leaves or not. Note the spectacular cone bracts, and the densely crowded cones that form head-like structures. Scale bars = 1 cm in Figs. 16–20. S =seed;L =leaf
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ephedroids from the Early Cretaceous Yixian Formation in Liaoning ...

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