科研之友
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摘要
A new genus and species, Celatheca beckii, is described from the Early Devonian (Siegenian) Posongchong Formation, Wenshan district of southern Yunnan, China. The plants consist of anisodichotomously divided vegetative or fertile axes. Divisions of the main axes produce irregularly to helically arranged lateral branch systems; vegetative ones are two to three times divided, and each unit ends in strongly recurved tips. Fertile lateral branches divide one to two times basally, and after a distance of 0.3-1.7 cm divide again twice closely and cruciately. Each of the four resulting segments consists of two parts, an inner elongate-oval sporangium and an outer adjacent leaflike appendage. The lobed distal ends of the leaflike appendages fold inward to enclose the sporangia so that the whole fertile structure appears coherent. Superficially the fertile structures resemble a synangium, but close examination shows the sporangium/appendage units are discrete structures joined only at the juncture of their stalks with the fertile axis. Comparison to the similar-appearing, presumed synangiate Yarravia shows the Chinese fossils to differ in having a smaller number of discrete sporangia and in the presence of the leaflike appendages forming a cupule-like covering. The sporangium/appendage organization is similar to that of some early cupulate ovules but probably is not homologous. This discovery further enriches the composition and diversity of the Posongchong flora and demonstrates another plant in which sporangia are protected by a modified vegetative structure. Its similarity to Australian Lower Devonian plants is discussed in view of current evidence of paleocontinental positions and early land plant biogeography.
- 出版日期1995-11
- 单位北京大学
