Systematics Section / ASPT
Yang, Yong .
The bract-scale and seed-scale complex of Ephedraceae.
The Gnetales have been considered closely related to angiosperms (e.g. Crane, 1985; Doyle and Donoghue, 1986; Nixon et al., 1994; Stefanovic et al., 1998), while recent multigenomic molecular systematic studies suggested that they are related to conifers, especially Pinaceae (the “gnepine” hypothesis, e.g. Chaw et al., 2000). The Gnetales include three extant monotypic families (e.g. Ephedraceae, Gnetaceae, and Welwitschiaceae), with Ephedraceae occupying a basal position (e.g. Gifford and Foster, 1989; Bowe et al., 2000). Ovules of the Gnetales bear additional envelope(s) that are unique within the gymnosperms while female reproductive organs are of great significance to systematics of gymnosperms (e.g. Florin, 1954; Yang and Fu, 2001). As a result, studies of female reproductive organs of Ephedraceae will be helpful to better understand the origin and evolution of the Gnetales.
Our recent detailed developmental studies suggest that female cones of Ephedraceae are compound, and the bract of female cones together with its axillary female reproductive unit constitute the bract-scale and seed scale complex (BSSC) of Ephedraceae comparable to that of conifers (e.g. Yang, 2001, 2004). The ancestral compound female cone of Ephedraceae was trimerous and bore secondary reproductive shoots in axils of bracts. At least two whorls of foliar components originally inserted on the secondary reproductive shoot. The proximal whorl was reduced at first. While the third abaxial foliar component of the second proximal whorl was reduced, two adaxial lateral foliar components gave rise to the cupule-like outer envelope by fusion. Derivation of the BSSC of Ephedraceae showed a different pattern from that of conifers and might parallel to that of conifers since they diverged from their Paleozoic common ancestor. It confirms a close relationship between the Gnetales and conifers but provides no evidence to the “gnepine” hypothesis. This scenario implies a new evolutionary pattern for the Gnetales.
1 - Institute of Botany, Chinese Academy of Sciences, Laboratory of Systematic and Evolutionary Botany and Herbarium, 20 Nanxincun, Xiangshan, Beijing, 100093, China
Bract scale and seed scale complex
Presentation Type: Paper
Location: Cottonwood C (Snowbird Center)
Date: Wednesday, August 4th, 2004
Time: 10:45 AM