Angiopteris sugongii (Marattiaceae), a new diploid species with transitional morphology between Angiopteris (sen. str.) and Archangiopteris

A new diploid species of marattioid ferns, Angiopteris sugongii Gui L. Zhang, J.Y. Xiang & Ting Wang (Marattiaceae), with ascending rhizomes, once pinnate to bipinnate laminae and marginal long sori, is identified and characterized from Southeast Yunnan, China. The distinctiveness between the new species and three relatives, A. itoi, A. bipinnata and A. sparsisora, are presented in detail, and a key to 11 species with once pinnate, or once pinnate to bipinnate laminae of Angiopteris in China is provided. Currently, there are three populations with 30 individuals in Daweishan National Nature Reserve and we suggest A. sugongii should be categorized as Critically Endangered (CR) species according to the criteria of IUCN. The discovery of this new species not only provides an important evidence for understanding the evolution of Angiopteris (sen. lat.), but also gives us a key insight into origin of species in the genus.