Format: ORAL

Qiaoping Xiang1, Tongxin Ye1, Xianchun Zhang1

1 Institute of Botany, Chinese Academy of Sciences, National Botanic Gardens, Beijing, P.R. China

Selaginellaceae is a Paleozoic origination with a cosmopolitan distribution. Previous fossil evidence indicates the rainforest floor origin of modern spikemoss and an ecological association between Selaginellaceae and the humid tropics since the Paleozoic. We observed a 99-million-year-old and well-preserved spikemoss branch with the character of resupinate strobilus in mid-Cretaceous Kachin amber, which provides a precious window to glimpse the Selaginellaceae diversification and its specialized habitat. To explore the resupinate strobilus evolution history, we built up the phylogeny including more than 85% resupinate strobilus species, estimated the divergence time, and reconstructed the ancestral state of the sporophylls arrangement and habitat. Resupinate strobilus first appeared in the Early Cretaceous within the Tropical Asia clade and later paralleled in other clade, with the occurrence times strongly related to the rise of angiosperm. In combination with their low-light adaptability and the difference in light response of dimorphic leaves, we further suggested that the current tropical spikemoss diversity originated since the Cretaceous (after angiosperm origin) instead of the evolutionary holdovers from the Paleozoic tropical forest and conjectured the resupinate strobilus was a key innovation of the ground-floor spikemoss adapting to the humidity and shadow rainforests.