Acianthella is a small genus of terrestrial orchids in the family Orchidaceae (order Asparagales), established in 2004 by David L. Jones and Mark A. Clements in The Orchadian (14:330–332). The genus belongs to the Acianthus alliance — a group of sympodial, ground-dwelling orchids native to the Australasian region.
Plants of Acianthella are terrestrial, sympodial herbs that lack true roots, instead bearing paired underground tubers and filamentous root-like structures. Each shoot produces a single leaf that is held horizontally well above the soil surface; the leaf base is sheathing and often lobed, with both surfaces green. The inflorescence is a terminal raceme bearing one to many resupinate flowers. A distinguishing feature of the genus is the labellum, which carries a flat longitudinal plate running from its base to the middle rather than the gland-like calli found in related genera. The pollinia are four in number, hard and waxy, and the rostellum is ventral.
The genus comprises approximately 7 species distributed across Australia and New Caledonia. Within Australia, species are restricted to Queensland and New South Wales. The genus is closely allied to Acianthus (mosquito orchids) and has been treated as a synonym of that genus in some classifications, including the Australian Plant Census.
Etymology
The genus name Acianthella is a diminutive derived from Acianthus, the closely related mosquito orchid genus. Acianthus itself is formed from the Greek akē or akis ("a point, needle") and anthos ("flower"), referring to the pointed perianth segments; the -ella suffix indicates a smaller or closely related genus.
Distribution
Acianthella is native to Australia and New Caledonia. Within Australia the genus is restricted to Queensland and New South Wales, where it occurs as an endemic element. Globally the genus contains approximately 7 species, with 2 of these endemic to eastern Australia.
Taxonomy Notes
Acianthella was described as a new genus by David L. Jones and Mark A. Clements in March 2004 (The Orchadian 14(7):330–332), segregated from Acianthus within the tribe Diurideae (family Orchidaceae). The Australian Plant Census (APC) treats Acianthella as a heterotypic synonym of Acianthus, while GBIF accepts it as a distinct genus. Other names published in the same period and now treated as synonyms include Univiscidiatus (Kores) Szlach. and Nemacianthops D.L.Jones & M.A.Clem. The taxon concept is anchored to the Jones & Clements 2004 protologue.
