XVI International Botanical Congess
Recent plant finds in Posongchong Formation (Pragian age, Early Devonian), southeastern Yunnan, China add a new dimension to the early diversification of land plants. Of the 15 genera thus far described, 11 are endemic to the area and 4 are cosmopolitan. Two new plants and additional members of Zosterophyllum are being studied. Some endemic forms exhibit either novel combinations of characters (centrarch protosteles and zosterophyll-like sporangia) or earlier appearance of characters than previously known (the presence of flattened, leaf-like structures). Several plants bear sporangia in strobili, one of the more complex showing sporangia with both an abaxial appendage and an overlying one. The presence of Zosterophyllum australianum, Baragwanathia sp., and a new species of Hedeia sinica indicate some similarity to the Upper Baragwanathia Flora of Australia. These data are included in a broad analysis of biogeography, initial results suggest that there is a northeastern Gondwana phytogeographic unit during the Early Devonian comprising Australia, South China and perhaps Shan Thai blocks.