The microsoroid ferns make up a large group in the family Polypodiaceae, easily characterized by the combination of at least partly clathrate rhizome scales and anastomosing reticulate venation. The diversification of this clade is poorly known, both because of unresolved generic delimitations and the lack of fossil records.
Dr. Frédéric MB Jacques and Prof. Zhou Zhekun’s group of Xishuangbanna Tropical Botanical Garden (XTBG) described the first fossil record of a microsoroid fern (Palaeosorum ellipticumsp. nov. F. M. B. Jacques & Z. K. Zhou.) found in the middle Miocene sediment of central Yunnan, southwest China. Its climate and ecological implications were also discussed.
The specimens were collected from Sanzhangtian Basin, Zhenyuan County, central Yunnan, southwest China (24.10°N, 101.22°E). The sediments belonged to the Dajie Formation dated as the middle Miocene. The fossil specimens consisted of a part and a counterpart of the same leaf.
The polypodiaceous fossil studied by them showed different affinities from the previously described polypodiaceous fossils. Palaeosorum ellipticum was therefore the first confirmed fossil record of the microsoroid ferns.
The fossil described in their study deepened the epiphytic fern history of Yunnan back to the middle Miocene. Their fossil showed that epiphytic ferns had been a component of the Yunnan forest for at least the last 10 million years. Subtropical forests with complex ecological relationships and structure had been established at least since the middle Miocene.
Fossil and modern microsoroid. A.C, Palaeosorum ellipticum F. M. B. Jacques & Z. K. Zhou (A, C, holotype, SZT乚0167a; B, SZT乚0167b). C,Details on the venation showing the reticulate venation and the club乚shaped hydathodes. D, E, Microsorum reticulatum Ching ex L. Shi (Sino乚Russianexpedition 3545, KUN). Scale bars . 1 cm.
Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences. Menglun, Mengla, Yunnan 666303, China
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