Origin and Differentiation of Endemism in the Flora of China
- WU Zheng-Yi , SUN Hang, ZHOU Zhe-Kun , PENG Hua, LI De-Zhu
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The paper analyzed 239 endemic genera in 67 families in the flora of seed plants in China . The results showed that there are five families containing morn than ten endemic genera , i. e ., Gesneriaceae (27 , number of endemic genera in China , same thereafter) , Composite (20) , Labiatae (12) , Cruciferae (11) , and Umbelliferae (10) , 15 families with two endemic genera, and other 30 families with only one endemic genus . Four monotypic families, i. e ., Ginkgoaceae, Davidiaceae , Eucommiaceae and Acanthochlamydaceae
, are the most ancient , relic and characteristic in the flora of seed plants in China . Based on integrative data of systematics, fossils histories, morphological and molecular evidence of these genera, their origination, evolution and relationships were discussed . In gymnosperms, all endemic genera are relics of the Arctic-Tertiary flora , having earlier evolutionary history, and can be traced back to the Cretaceous or to the Jurassic and even earlier . In angiosperms, the endemic genera are mostly relic, and are represented in all lineages in our Eight-Class System of classification of angiosperms , and endemism can be found in almost every evolutionary stage of extant angiosperms . The relic genera once occupied huge areas in North Hemisphere in the Tertiary or the late Cretaceous, while neo-endemism was mostly originated in the late Tertiary . They came from Arctic-Tertiary , Paleo- tropical-Tertiary and Tethys-Tertiary florisitic elements and the blend of the three elements, with many genera of autochthonous origination . The endemism was formed when some dispersal route such as the North Atlantic Land Bridge, and the Bering Bridge became discontinuous
during the Tertiary , as well as the climate change and glaciation in the late Tertiary and the Quaternary . Therefore , the late Tertiary is the starting point of extant endemism of the flora of China .