The end-Permian mass extinction is the greatest biotic crisis in Earth history causing the extinction of a large number of marine and terrestrial animals globally. However, how land plants responded to the catastrophe remains controversial. The successive plant-bearing beds in China provide a unique window into the great vegetation change through the critical Permian-Triassic time interval. A notable monospecific vegetation comprising a new isoetalean, Tomiostrobus sinensis Feng, is documented

more »

... rom the lowermost part of the coastal Kayitou Formation in Southwest China. The new plant is a diminutive, heterosporous lycophyte, which formed ground-covering communities infringing the oligotrophic lakes along coastal regions. The apparent occurrence of T. sinensis immediately above the uppermost coal bed demonstrates that the enigmatic gigantopterid-dominated rainforest ecosystem suddenly collapsed and was replaced by the isoetalean-dominated herbaceous vegetation in the tropics of the eastern Tethys. Our study indicates that the magnitude of vegetation response to the end-Permian mass extinction in different palaeophytogeographic regions is probably largely affected by the latitudinal gradients of biodiversity and ecological stress. Because of the complexity of local palaeoenvironmental, palaeoclimatic and palaeotopographic conditions, it is unlikely that a unified global pattern and timing of land plant response to the end-Permian mass extinction can be obtained. J o u r n a l P r e -p r o o f Among the iconic representatives of the early Mesozoic isoetaleans, the Pleuromeia and Lepacyclotes groups are recognised as cosmopolitan plants during the late Early and Middle Triassic Wang, 1982, 1990; Meng, 1994; Grauvogel-Stamm and Ash, 2005; Feng et al., 2018) , whereas Tomiostrobus has been sporadically recognised thus far only from the lowermost Triassic of high J o u r n a l P r e -p r o o f Journal Pre-proof J o u r n a l P r e -p r o o f Journal Pre-proof In the terrestrial settings, the Kayitou Formation is conformably overlain by the terrestrial Dongchuan Formation (Shen et al., 2019; Tong et al., 2019). Conchostracans obtained from the Kayitou Formation in the Lubei and Mide sections of Yunnan, and Zhejue, Jingzhong, Chahe, Jiucaichong and Xiaohebian sections of J o u r n a l P r e -p r o o f Journal Pre-proof J o u r n a l P r e -p r o o f Journal Pre-proof The specimens illustrated in this paper are housed in the Palaeobotanical Collections