Adiantum membranifolium (Pteridaceae), a new record of maidenhair fern from Laos

Adiantum membranifolium S.Linds. & Suksathan is a species of maidenhair fern previously known only from a few shady limestone cliffs in Western, Northern, and North- Eastern Thailand. Recently, an exploratory survey in Khammouane Province, Laos led to the discovery of this species thriving on a limestone cliff with flowing water during the rainy season, a finding that extends its known geographical distribution. This species is characterised by having single or 1-pinnate fronds, pinnae that are deeply cleft up to or more than half of the length of pinnae, and terminal pinnae with basal angle usually ranging from 45–180° and larger than lateral pinnae. A key to Adiantum L. in Laos and a description with photographs and illustrations are also provided. Epidermal features of A. membranifolium are described here for the first time.