Arachniodes is a genus of terrestrial, evergreen ferns in the family Dryopteridaceae (the wood ferns), subfamily Dryopteridoideae, and order Polypodiales. The genus was first described by the Dutch-Belgian botanist Carl Ludwig von Blume in 1828, based on the Indonesian species Arachniodes aspidioides, but remained obscure until 1961 when Mary Douglas Tindale transferred additional species into it from the genus Byrsopteris. The Pteridophyte Phylogeny Group classification of 2016 (PPG I) recognises approximately 60 species, while the Checklist of Ferns and Lycophytes of the World accepts 78 species as of 2020. Several species in the genus are commonly known as holly ferns.
Plants are medium-sized to large, growing from rhizomes that range from long-creeping to short-ascending or rarely erect, covered in dense scales. Fronds are typically long-stalked, with the stipe equalling or exceeding the lamina in length. The lamina is usually deltoid, ovate, or pentagonal in outline and 2–4(or 5)-pinnate, with a papery to leathery texture; a simply pinnate form occurs in a few species. Veins are free and pinnate or forked, often ending in a hydathode. Sori are orbicular, borne terminally or on the upper (acroscopic) branches of veinlets, each covered by a persistent orbicular-reniform indusium. The chromosome base number is x = 41.
The genus is distributed across tropical and subtropical regions worldwide, with its greatest diversity concentrated in eastern and southeastern Asia. China alone hosts around 40 species, 18 of which are endemic.
Etymology
The genus name Arachniodes derives from the Greek arachne (spider or spider's web) and the suffix -oides (resembling), likely alluding to the filiform, web-like scales that densely cover the rhizome and stipe base.
Distribution
Arachniodes is distributed across tropical and subtropical regions worldwide, but its diversity is concentrated in eastern and southeastern Asia. China harbours roughly 40 species (18 endemic); the genus also occurs in Japan, Southeast Asia, the Pacific islands, and parts of Africa and the Americas.
Taxonomy Notes
Arachniodes was published by Blume in 1828 (Enum. Pl. Javae 2: 241) on the basis of a single Indonesian species, A. aspidioides. The genus was not broadly adopted until Tindale (1961) transferred Byrsopteris amabilis and B. aristata into it. Under PPG I (2016) the genus is placed in Dryopteridaceae subfamily Dryopteridoideae. Species counts vary by authority: PPG I accepts ~60 species; the Checklist of Ferns and Lycophytes of the World (2020) accepts 78. Some hybrids are also recognised. The chromosome base number x = 41 is consistent across the genus.
