Polystichum oligodontum (subg. Haplopolystichum, Dryopteridaceae), a new cave fern from Guangxi, China

Polystichum oligodontum (Dryopteridaceae), a new fern species in P. subg. Haplopolystichum from three karst caves in northwest Guangxi, China, is described and illustrated. This species is unique in having pinnae with a shallow or nearly free lobe on the acroscopic base and coarsely toothed distal margins.

It resembles P. membranifolium and P. kwangtungense in its reflexed and oblong pinnae with an obtuse or rounded apex, but can be easily distinguished by its remote pinnae bearing a lobe at the acroscopic base. The new species also somewhat resembles P. leveillei in the nearly free basal lobe, but differs by its toothed upper pinna margins. Molecular phylogenetic analysis of 56 Polystichum species, based on the rbc L gene, supports the placement of P. oligodontum within P. sect.

Sphaenopolystichum, with P. alcicorne as its closest relative. According to the IUCN Red List Categories and Criteria, the new species is assigned to the Critically Endangered (CR) category.