Fossil Records Of Ephedra And Its Early Diversity

The phylogenetic position of Gnetales has always been the bone of contention for the international botanists for hundreds of years. Some authors hold that this group is the sister group of angiosperm, but others suggest its affinity is near to other gymnosperm. Despite these disputes, the Ephedra (Ephedraceae) was considered to be plesiomorphic in Gnetales. Many different studies had been carried out on genus Ephedra at different angle for its special phylogenetic affinity, such as anatomy, morphology and taxonomy, molecular systematics, and palaeobotany as well. When studying the systematic development and evolutionary position, we realized the records of Ephedra are not only the key to the other study on Ephedra but also the urgent affairs nowadays. Such important questions should be understood before the satisfactorily resolution of the fossil records of Ephedra: â‘  What is the time of Ephedra? â‘¡ What are the fossil records of Ephedra? â‘¢ What is the biodiversity of Ephedra in Early Cretaceous? We collected all the references on the fossil records of Ephedra round the world, which provide us well foundation for our study on the fossil records of genus Ephedra; new well-preserved specimens have been collected in western Liaoning Province, northeastern China, which provide us new data on our study of the fossil records of genus Ephedra. After our throughout study on genus Ephedra, combined with the study on new specimens collected at Early Cretaceous Beds, Jianshangou Formation, Western Liaoning Province, China, we draw conclusion as following: (1) The characteristics for Ephedrites and Alloephedra which were put under Ephedraceae were quite same as those of Ephedra. The only difference between Ephedrites and Ephedra was the difference in age, and the difference between Alloephedra and Ephedra was the branch pattern in Alloephdra covered both opposite and alternate. The throughout comparison resulted in the merger of Ephedrites and Alloephedra into Ephedra. (2) The fossil records of Ephedra had been studied based on the features of reproductive organs, and showed that only 7 species can be ascertained: Ephedra chenii (Cao et Wu) Liu, Li et Wang comb. nov., E. antiqua (Heer) Liu, Li et Wang comb. nov., E. xingxuei (Tao et Yang) Liu, Li et Wang comb. nov., E. lanceolata Liu, Ferguson, Li et Wang sp. nov., E. divisa Liu, Ferguson, Li et Wang sp. nov., E. ovata Liu, Ferguson, Li et Wang sp. nov., and E. tenera Liu, Li et Wang sp. nov.. The rest had been put aside for either unclear features or lack of reproductive features. (3) The comparative study on these fossil specimens shows that great diversity has been shown on Ephedra at 125 million years ago. The diversity including: the shape, size and venation for leaves and the morphology for bracts in seed units. The leaf shape of them (with four types: ovate, divided, lanceolate and scalelike) at 125 million years ago is more complex than living plants (with two types: lanceolate and scalelike). The leaf venation at that time is forked, comparing with recent plants with parallel and anastomosed venation.The leaf size of the early plants is larger (up to 35mm long and 45 mm wide) than that of modern ephedras (up to 35 mm long and 2 mm wide), and the bract shape in seed units is much narrower (scalelike and lanceolate) than that in modern plants (ovate to oblong). So, the Ephedra at 125 million years ago showed greater diversity than that of living plants. The comparison of features between extant and fossil species suggests that Ephedra has experienced a process of evolution in the past 125 million years, and some features died away and some species has extincted. At the same time, the appearance of Ephedra with comparatively large leaves shows the existence of warm and humid microhabitat under the hot and dry environment (4) The age of Ephedra was estimated as 8-32 million years by the Chloroplast rbcL sequence data. A quite recent study based on molecular analysis (rbcL, rps4 and ITS) and fossil seeds of Ephedra as well as ephedroid pollen suggested the age for Ephedra is about 110 million years. The reliable evidence based on the well-preserved specimens suggests that Ephedra appeared at least 125 million years ago, and great diversity had been exhibited at that time, which implies that the age for Ephedra may be earlier.