Polystichum yaanense (Dryopteridaceae), a Remarkable New Species from Sichuan, China

A new fern species, Polystichum yaanense Liang Zhang & Li Bing Zhang (Dryopteridaceae), is described from Bifengxia, or the Bluish Green Peak Canyon, in Ya'an Prefecture in Sichuan Province, China. The new species is morphologically unique in having yellowish green leaves, a thin but. firm leaf texture, veins visible on the adaxial leaf surface, and narrowly ovate to lanceolate rachis scales. Ecologically, the new taxon grows in acidic soils, in contrast to other species in section Haplopolystichum Tagawa. Polystichum yaanense is considered to be Critically Endangered (CR), based on IUCN Red List criteria. Ten other species of Polystichum Roth occur in the type locality within the same canyon; all 11 species are distinguished from one another by a dichotomous key based on morphology.