Systematics And Evolution Of Ephedra L.(Ephedraceae) From China

The genus Ephedra L. (Ephedraceae) is one of the three extant genera of the Gnetales. The systematics and evolution of the genus has been one topic of many studies in the past several decades and remain unresolved. The present thesis is a comprehensive study on all species of Ephedra from China based on morphological, anatomical, ontogenetic characters and fossil evidence with a focus on the taxonomy, the evolution of the female cones, and the ecology and distribution patterns of the genus.1. TaxonomyVariation patterns of all available characters in Ephedra from China are studied both in the field and in herbarium. Thirteen species are recognized from China, among which, Ephedra rituensis Y. Yang, D. Z. Fu et G Zhu is described new to science. The traditionally accepted species, E. likiangensis and E. fedtschenkoae are recognized as synonyms of E. saxatilis and E. monosperma respectively. The identities of five traditionally confused species, E. regeliana, E. sinica, E. distachya, E. intermedia and E. glauca are elaborated.2. MorphologyAll Ephedra species from China are illustrated with great details on male and female cones. The photographs provide valuable information of characters including peduncle of cone, bract, and micropylar tube etc. for classification and identification of Ephedra species from China. Ephedra lomatolepis is demonstrated to belong to sect. Pseudobaccatae because the bracts of its female cones are fleshy at maturity.3. MicromorphologySeed, synangium, and branchlet surface sculpture of some Ephedra species are studied using SEM and described for the first time, and their systematic significance is discussed.Four types of seed surface sculpture are described: Type I is smooth (E. intermedia, E. distachya, E. regeliana), Type II possesses warty structures (E. equisetind), Type III bears transverse laminar protuberances (E. rhytidospermd), and Type IV is striated (E. gerardiana, E. saxatilis, E. minuta).Study on branchlet surface sculpture does not reveal any hair-like structures as recorded by previous authors; only some warty cuticles on the ridges and variable stomata in the grooves are noted.The surface of synangium in Ephedra has secondary sculpture while the lip of the openings of synangium resembles the cerebral waves. This character is distinct in seed plants and is useful in fossil identification for the Ephedraceae.4. PalynologyPollen of Ephedra from China is studied. Four types of pollen have been found in the genus, namely Type A, B, C, and D, according to the number and structure of ridges and structural characters of grooves. The results indicate that E. rhytidosperma bears pollen with 5 waved ridges and developed hyaline lines in the grooves, which is typical for Type A of pollen morphology in the genus. The evolution of pollen of the genus is discussed. It is considered that the evolutionary tendency of pollen morphology in Ephedra is from Type D to Type A.5. OntogenyThree types of female cones of Ephedra are recognized according to the number of seeds per cone, namely uni-ovulate cone, bi-ovulate cone, and tri-ovulate cone. It is suggested that terminal bud of primary cone axe is developed in tri-ovulate cone and disappears in bi-ovulate cone. In the most extreme condition in uni-ovulate cone, the female reproductive unit (FRU) occupies the position of the terminal bud. An evolutionary trend of reduction is supported in the genus from tri-ovulate to uni-ovulate cone, in which the bract number and seed number are reduced, and the seed size and seed surface sculpture are increasing.6. AnatomyEphedra rhytidosperma is studied in detail. The FRU surface is smooth in its early developmental phases, while the laminar structure is secondary. The secondary sculpture is formed by the outgrowth of the outer tangential wall of the epidermal cell, and this kind of protuberance always occurs in the adjoining cells, which makes the laminar protuberances. The transverse and longitudinal section of the developing ovulate structure...