REINVESTIGATION ON THE FOLLICLE FOSSILS OF FIRMIANA (MALVACEAE) FROM THE MIOCENE SHANWANG FORMATION OF SHANDONG PROVINCE
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Abstract:
Firmiana Marsili comprises ca. 16 species currently distributed in tropical to subtropical areas of eastern Africa and east-ern-southeastern Asia, and is widely cultivated in southern and northern China. Follicles of Firmiana are readily distin-guishable since they are dehiscent at maturity with dehiscent carpel foliate and membranous. However, follicle fossils of Firmiana are very rare and have been only known from the lower Miocene of Linqu, Shandong, East China and the upper Miocene of Lincang, Southwest China. Here we examine the follicle fossils of Firmiana from the lower Miocene Shanwang Formation of Linqu County, Shandong Province and find that the Miocene Shanwang flora includes two species of Firmi-ana—Firmiana sinomiocenica Hu and Chaney and F. yunnanensis Xie and Manchester. The specific diagnosis of F. sinomi-ocenica was emended based on the additional well-preserved seed-bearing fruit fossils. These new materials indicate that Firmiana already has a certain diversity in east China during the early Miocene. Firmiana sinomiocenica is the most similar to the living species F. simplex (L.) W. Wight in morphology, which suggests that F. simplex is a relatively primitive species in the genus. The sizes of carpels and seeds of F. sinomiocenica indicate that the chromosome ploidy of fossil Firmiana that occurred around 17 Ma was likely similar to that of extant F. simplex. Remarkably, the boat-like shape and membranous folli-cle favors wind dispersal. Together with other winged fruits, the Firmiana fossil fruits suggest that wind dispersal was well represented in the early Miocene Shanwang flora.
