About Adiantum reniforme L.
Adiantum reniforme, commonly known as the kidney-leaved maidenhair fern, is a fern species in the maidenhair genus Adiantum, belonging to the family Pteridaceae. It grows in sheltered rock crevices and on walls. This species is native to Madeira (its type locality), the Canary Islands, and Cape Verde islands; it also grows in scattered populations across East Africa, Madagascar, the Mascarene Islands, the Comoros, and a small number of relict sites in Chad's Tibesti region. Its leaves are large and round, with dichotomous venation, and have a very narrow red edge that corresponds to the marginal indusium on the leaf underside. Different taxonomic authorities accept different circumscriptions of this species, with varying numbers of accepted subspecies and varieties. The Plants of the World Online (POWO) database accepts two subspecies and one variety: Adiantum reniforme subsp. reniforme, which occurs in Madeira, the Canary Islands, and additionally in Cape Verde, Chad, DR Congo, Kenya, Malawi, and Tanzania; Adiantum reniforme subsp. pusillum (Bolle) Rivas Mart., which occurs in the Canary Islands and Madeira; and Adiantum reniforme var. asarifolium (Willd.) Sim, which occurs in Mauritius and Réunion. POWO does not specify which of the two subspecies this variety belongs to. In contrast, a study by Ai-Hua Wang et al. proposes accepting only two varieties: Adiantum reniforme var. reniforme from the Canary Islands and Madeira, and Adiantum reniforme var. asarifolium found in continental Africa and Indian Ocean islands including Madagascar, Seychelles, Comoros, and Réunion. A similar Adiantum taxon found only in the Three Gorges area of Wanzhou, Chongqing, China was formerly treated as a Tertiary relict variety of this species, under the name Adiantum reniforme var. sinense. This taxon has since been raised to full species rank as Adiantum nelumboides, the lotus-leaved maidenhair fern, which is threatened with extinction due to habitat destruction caused by the Three Gorges Dam.
