A small genus with one species to Australia. These terrestrial orchids grow in loose groups, usually in wet conditions. The plants have a long fleshy rhizome instead of tubers and a single, bright green, hairless leaf, held erect on a brittle stalk. The single white flower measures 2-3 cm in width. The lateral sepals and petals spread in a starry fashion with the deeply concave dorsal sepal covering the labellum. The distinctly three-lobed labellum is firmly hinged to the column base, with prominent red transverse bars and central rows of yellow calli. The slender incurved column has fused column wings. Adenochilus flower early to mid summer, growing in specialized habitats with restricted distribution in New South Wales.
Similar Genera
Stegostyla
Significant Generic Characters
Deciduous terrestrial; root system consisting of long fleshy non-tuberous rhizomes; leaf single, glabrous, erect; scape and ovary glabrous; flower solitary, resupinate, white; dorsal sepal larger than the lateral sepals; lateral sepals fused at the base; petals held erect beside the labellum; labellum with a sharp medial fold; main calli in rows with smaller scattered supplementary calli; column wings fused, with broadly toothed apices extending above the anther.
Size and Distribution
A genus of 2 species, one endemic to Australia, the other to New Zealand. The Australian species, Adenochilus nortonii has a relatively restricted and patchy distribution in New South Wales, occurring on the New England Tableland and Barrington Tops (between 30°30' S and 32° S), in the Blue Mountains at about 33°43' S and with a southerly record near Bundanoon (34°39' S). Altitudinal range 500-1500 m. State occurrence: New South Wales.
Ecology
Adenochilus nortonii usually grows in mesic conditions in upland to montane districts but in very different habitats at each end of its range. In the northern part of its range it grows in sphagnum mounds and among other moss species and leaf litter in high rainfall forest dominated by Nothofagus moorei. By contrast in the Blue Mountains to the west of Sydney and near Bundanoon it grows among moss and forbs in sheltered wet crevices, clefts and overhangs of sandstone cliffs. In both habitats the rhizomes of the orchid mostly grow through the lower layers of moss pads and decaying litter. Soils are moisture-retentive and fibrous from decaying litter and the roots of adjacent shrubs.
Biology
Pollination: The flowers of Adenochilus nortonii are insect pollinated but the pollinating vector is unknown. Bower (2001), using the floral morphology, suggests that food deception is the probable attracting mechanism for the pollinator. Autogamy and apomixis are unknown in the genus.
Reproduction: Adenochilus nortonii reproduces from seed. Local clonal patches are formed by fracture or decay of the elongated rhizomes. Seed dispersal takes 8-12 weeks from pollination. There is no increase in the length of the pedicel or peduncle during this process.
Seasonal Growth: The prevailing climate where these orchids grow is seasonal with hot summers and cold winters. The orchid plants grow actively in spring and early summer with the sterile leaves and leaf-bearing inflorescences emerging at the same time and the leaves expanding as the inflorescences develop to flowering.
Flowering: The plants flower early to mid-summer.
Hybrids: Intergeneric hybrids involving Adenochilus are unknown.
Fire: This orchid does not grow in habitats which are prone to fires.
Derivation
Adenochilus is derived from the Greek aden, gland and cheilos, lip and refers to the labellum calli which are prominent in these orchids.
Botanical Description
Perennial geophytic herbs, sympodial. Plants glabrous. Rhizome subterranean, long creeping, horizontal, fleshy, irregularly cylindric, enlarged at each growing point, lacking papillae. Roots absent. Rhizoids present. Tubers absent. Stem erect, short, unbranched, with a membranous cataphyll at each node. Leaf lasting a single season, 1 per shoot, either basal and petiolate or cauline and sessile on the proximal third of a scape. Leaf lamina membranaceous, flat, convolute in bud, hypostomatic, margins entire, apex apiculate. Venation anastomosing, the main veins uniting apically. Petiole fleshy, very shallowly grooved. Inflorescence racemose, 1-(2)-flowered, erect, terminal. Peduncle glabrous, fleshy, with 1 or 2 foliaceous sterile bracts. Floral bracts foliaceous, small. Pedicel short, glabrous. Ovary elongate, ribbed, glabrous. Flower resupinate, pedicellate, white internally, the exterior surface of all segments with red sessile glandular hairs, a few stalked glandular hairs towards the base of the segments. Sepals and petals dissimilar. Dorsal sepal free, much broader than the lateral sepals, incurved and strongly cucullate over the column. Lateral sepals united at the base, narrower than the dorsal sepal, porrect. Petals free, narrower than the sepals, held erect beside the dorsal sepal. Labellum free, stiffly hinged by a short claw to the anterior column base, markedly dissimilar in size and shape to the sepals and petals, ecalcarate. Labellum lamina membranous, with a sharp medial fold, distinctly lobed; margins entire. Calli clavate, subsessile and stalked, the larger ones yellow to orange, in a narrow central band extending from the labellum base to its apex; basal calli clustered; smaller white calli scattered on the lamina lateral to the main central band. Nectar absent. Spur absent. Column lacking free filament and style, slender, incurved, with red sessile and stalked glandular hairs. Column foot absent. Pseudospur absent. Column wings fused completely, with broadly toothed apices which extend above the anther. Anther terminal, 2-celled, persistent, basifixed, erect, not rostrate. Pollinarium absent. Pollinia 8, bilobed, mealy, cream. Viscidium absent. Rostellum ventral, transverse. Stigma entire, small, concave. Capsules dehiscent, smooth, erect; pedicels not elongating in fruit; peduncle not elongating in fruit. Seeds numerous, light coloured, winged.
Notes
This orchid has a restricted distribution and grows in specialised habitats.
Nomenclature
Adenochilus Hook.f., Fl. nov.-zel. 1: 246 (1853). Type species: Adenochilus gracilis Hook.f.
Infrageneric Taxa: No infrageneric taxa are recognised.
References
Bishop, T. (1996). Field Guide to the Orchids of New South Wales and Victoria. University of New South Wales Press, Sydney.
Bower, C.C. (2001). Pollination p. 87, in Pridgeon, A.M., Cribb, P.J., Chase, M.W. & Rasmussen, F.N. (eds), Genera Orchidacearum, vol. 2: Orchidoideae. (part one). Oxford University Press, United Kingdom.
Clements, M.A. (1990). Catalogue of Australian Orchidaceae. Austral. Orch. Res. 1: 1-160.
Harden, G. (ed.) (1993). Flora of New South Wales, vol. 4. New South Wales University Press, Sydney.
Nicholls, W.H. (1969). Orchids of Australia. Thomas Nelson, Melbourne.
Rupp, H.M.R. (1943). The Orchids of New South Wales. Australian Medical Publishing Coy, Sydney.