Adenochilus, commonly known as gnome orchids, is a small genus of two species of terrestrial orchids in the family Orchidaceae (order Asparagales). One species, Adenochilus gracilis, is endemic to New Zealand, while the other, Adenochilus nortonii, is restricted to south-eastern Australia. The genus was first formally described in 1853 by the botanist Joseph Dalton Hooker, whose account appeared in Flora Novae-Zelandiae; A. gracilis was described in the same publication and designated as the type species.
Plants in this genus are perennial, deciduous, and sympodial herbs that grow from a long, thin, horizontal underground rhizome. Each flowering stem bears a single leaf — attached either by a long stalk or directly to the stem — and terminates in a single resupinate flower. The dorsal sepal is free and arches forward to form a hood over the labellum and column. The lateral sepals and petals are also free from one another, longer and narrower than the dorsal sepal, and spread widely apart. The labellum is similarly free, attached at the base of the column by a short stalk or claw, and is curved with a distinctive narrow central band of yellow glandular calli — the feature that gives the genus its name.
Adenochilus gracilis is widespread across both the North and South Islands of New Zealand, as well as Stewart Island and the Chatham Islands, where it typically grows in deep leaf litter beneath beech trees or near wetland margins. Adenochilus nortonii has a much more restricted range in the Blue Mountains, Barrington Tops, and Point Lookout areas of New South Wales, at elevations between 400 and 1,000 metres, frequently beneath Antarctic beech (Nothofagus moorei).
Etymology
The genus name Adenochilus is formed from the Ancient Greek words aden ("gland") and cheilos ("lip"), a reference to the narrow band of glandular calli (the yellow, wart-like protuberances) found on the labellum of both species in the genus.
Distribution
Adenochilus gracilis occurs throughout New Zealand — on the North Island, South Island, Stewart Island, and the Chatham Islands — most commonly in deep leaf litter under southern beech (Nothofagus) forest and occasionally near wetlands. Adenochilus nortonii is confined to a small area of New South Wales, Australia, in the Blue Mountains, Barrington Tops, and Point Lookout regions at altitudes of 400–1,000 m, frequently growing under Antarctic beech trees.
Ecology
Both species are shade-tolerant terrestrial orchids associated with cool, moist forest understoreys — A. gracilis with beech-dominated forest and wetland margins in New Zealand, and A. nortonii with montane Antarctic beech forest in eastern Australia.
Taxonomy Notes
The genus Adenochilus was established by Joseph Dalton Hooker in 1853 in Flora Novae-Zelandiae, with A. gracilis as the type species described in the same work. It belongs to the family Orchidaceae, order Asparagales, and comprises only two accepted species, giving it one of the smallest genus circumscriptions in the Australasian orchid flora.
