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

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256 C. Rydin et al.: Cretaceous ephedroids from China Fig. 21. Reconstruction of Liaoxia chenii, Cao et S.Q. Wu (emerd. Rydin, S.Q. Wu et Friis) based on the holotype (PB17800) and the new specimens (PB20717–PB20718). Drawing by Pollyanna von Knorring. Scale bar = 1 cm The cones of L. acutiformis and L. changii contain more bracts (6–12 in the former, 6–10 in the latter), but each bract is smaller and has a less distinctly pointed, acute apex. In L. elongata the cones have c. 10 pairs of pointed, narrowly ovate bracts. Several cones of Liaoxia robusta have approximately 4 pairs of cone bracts but there are also larger cones with up to 10 bract pairs. The cones of L. longibractea consist of only 1–2 pairs of bracts, which are very long and conspicuous with their extended, narrow apex. They are unique among ephedroid plants, we have not seen anything similar in any living or fossil species. The cones of extant Ephedra are compound, consisting of cone bracts and seeds with extra-integumentary structures of bract (leaf) origin (Pearson 1929, Crane 1985, Takaso 1985, Pedersen et al. 1989, Yang 2001, 2004). Our interpretation is that the cones of Liaoxia are also compound with the same structural arrangement as those of Ephedra, but the preservation of the material prevents unambiguous conclusions. Ephedra cones are generally composed of 2–8 pairs of bracts, sometimes more. This is in agreement with the condition in the fossil species, even though the large specimen of L. elongata has more bracts than usually seen in extant Ephedra. Many extant species have obovate to rounded cone bracts with an obtuse or rounded apex, but ovate bracts with a pointed apex also occur in some species. Seeds. Seeds are preserved as compressions or impressions in several of the fossils, even though no anatomical details are preserved. Like extant Ephedra, Liaoxia chenii has seeds only in the axil of distal bract. The cone bracts are delicate and were probably membranous, not fleshy. They are often fully reflexed, and several cones seem to lack seeds, indicating wind dispersal and preservation at a late stage in the reproduction phase. Delicate cone bracts with two veins that become reflexed at seed maturity can for instance be seen in the African species Ephedra alata. Contrary to the cones of Liaoxia chenii and extant Ephedra, the cones of L. changii, L. robusta and L. longibractea appear to have a seed in the axil of most bracts, also in proximal part of the cones. This is interesting as it differs significantly from Ephedra, which has seeds mainly in a distal position, but is more similar to Welwitschia where seeds also occur proximally in the cone. This is conceivably an ancestral state present in some of the Cretaceous fossils and retained in Welwitschia, (but see also the discussion below on the distinction between ephedroid and welwitschioid fossils). In Liaoxia chenii and L. changii, the seeds are ovoid to elliptic and small. In Liaoxia robusta, and L. longibractea they are rounded
C. Rydin et al.: Cretaceous ephedroids from China 257 to elliptic and larger, but all the fossil seeds are much smaller than seeds of extant Gnetales. Seeds of Ephedra are at least 6–7 mm long whereas the fossils are only 1–4 mm. The small size of the fossil seeds is, however, in accordance with other ephedroid seeds from the Early Cretaceous described from Portugal and North America (Rydin et al. 2004, Rydin et al. 2006). Gender. Most species of Ephedra are dioecious with male and female reproductive parts on separate plants. Male cones often comprise more bracts than female cones of the same species and the shape of male and female cone bracts may differ within a species. All Liaoxia specimens currently known have only one kind of cones and we therefore assume that these ephedroid fossils were also dioecious. Liaoxia chenii, L. changii, L. robusta and L. longibractea are clearly female plants. Their cone bracts are reflexed and seeds are present in the axil of bracts. In contrast, Liaoxia acutiformis and L. elongata have bracts that are more erect and without remains of seeds or microsporangiophores. The poor preservation makes interpretation of reproductive details difficult, but the absences of seeds and the erect position of the cone bracts might suggest that L. acutiformis and L. elongata represent male plants. Male organs of extant Ephedra generally detach easily, shortly after pollination, which may explain the absence of preserved microsporangia in these putatively male plants. Because the Early Cretaceous ephedroids are interpreted as dioecious, it is possible that the putatively male specimens actually belong to the same species as one or two of the female specimen. To explicitly correlate female and male plants would require epidermal or other cellular details not present in this material. It is, however, interesting to note that Liaoxia acutiformis is vegetatively closely similar to L. chenii, but differs in the number and shape of the cone bracts. Liaoxia acutiformis may be very closely related to L. chenii, speculatively, the male plant of L. chenii. Similarly, Liaoxia changii and L. elongata are vegetatively similar, both lacking leaves, but differ in shape of cones and cone bracts. Both species have been found in the Fanzhangzi Section in Lingyuan and, again speculatively, Liaoxia elongata could be the male plant of Liaoxia changii. Other gnetalean fossils from eastern Asia. Several ephedroid fossils, other than those described here, have been reported from China and else where (Table 3). Among them are Ephedrites sinensis and Ephedrites exhibens (Wu et al. 1986) from the Jurassic Xiaomeigou Formation of Qinghai. The fossils are fragmentarily preserved and difficult to compare with the present material, but they seem to differ from Liaoxia species in having only a single pair of seeds and bracts. Alloephedra xingxuei (Tao and Yang 2003) from the Dalazi Formation, China, is an Early Cretaceous fossil interpreted as a close relative of Ephedra. However, the nature of branching and reproductive structures is not fully clear from descriptions and illustrations and there are features that are not compatible with the Gnetales (e.g. possibly alternate branching). Ephedra archaeorhytidosperma (Yang et al. 2005), collected from the Jianshangou Bed that also contains Liaoxia chenii and L. robusta, is clearly ephedroid with striate stems, opposite branching, terminal female cones consisting of 1–2 seeds with extended micropylar tubes and bracts or bract scars. Ephedra archaeorhytidosperma differs from most of the Liaoxia species presented here in that each cone consists of only 1–2 seeds and bract pairs, whereas the Liaoxia fossils have cones with more bracts. Liaoxia longibractea has cones with few bracts but the very long and narrowly extended cone bracts of L. longibractea are very different from those of Ephedra archaeorhytidosperma. The material of Ephedra archaeorhytidosperma comprises one associated triangular leaf, which is poorly preserved and not clearly attached to the specimen. There is no evidence of leaves at the nodes. Thus Ephedra archaeorhytidosperma may lack leaves, as do some species of Liaoxia. Sun et al. (2001) described two new species of ephedroid fossils from the Yixian Formation of Liaoning. Branching in Ephedrites
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