裸子植物雄球花——纤细堆囊穗的修订(英文)

Emendation of Sorosaccus gracilis Harris 1935, a gymnospermous pollen cone

研究了采自中国东北晚三叠世羊草沟组的一种裸子植物雄球花——纤细堆囊穗。通过对新材料的研究,发现这种雄球花小孢子叶末端的裂片在形态上差异很大,这是原来没有发现的十分重要的特征。这些保存精美的化石对于纤细堆囊穗特征的阐明和修订以及物种复原很有帮助。将中国的标本与西伯利亚堆囊穗、小堆囊穗、乌尔马堆囊穗和被定为长叶拜拉的雄球花进行了比较,发现它们与纤细堆囊穗在特征上一致,故将它们处理为纤细堆囊穗的异名。修订后的纤细堆囊穗包括上面所提到的所有种。同时,也讨论了堆囊穗属可能的演化意义。它可能是银杏属的远祖,经过小孢子囊数目的减少和小孢子叶长度的缩短而演化到现在的银杏,而产自辽西早白垩世的辽宁银杏可能代表了堆囊穗和现代银杏在形态演化上的一个中间步骤。

Study of gymnospermous pollen cones, identified with Sorosaccus gracilis Harris 1935, from the Yangcaogou Formation, Late Triassic of China, has led to the identification of new and significant characteristics of the species. The new specimens show distinct variations in the morphology of the distal laminar portions of the microsporophylls. These well-preserved fossils are helpful in elucidating, reconstructing and revising the diagnostic features of S. gracilis. After comparing the characteristics of the specimens from China with those of S. sibiricus Prynada 1962, and of the pollen cones which were respectively assigned to Baiera longifolia (Pom.) Heer 1876 from Siberia, Russia, S. minor Harris 1935 from Greenland, and S. umaltensis Krassilov 1972 from Bureya River of Russia, we consider that these four names should be reduced to the synonymy of S. gracilis. Thus we revise the diagnosis of Sorosaccus. The significance of Sorosaccus in evolution of pollen cones is discussed. We consider that Sorosaccus is possibly basic to the evolution of the genus Ginkgo by the reduction of the number of microsporangia and of microsporophylls. Ginkgo liaoningensis Liu, Crane, Li S Wang 2005 from the Early Cretaceous of Liaoning Province, China represents likely one of morphologically intermediate steps between Sorosaccus and G. biloba in evolution.