Clumping epiphytes with short onion-shaped pseudobulbs surrounded by a mass of thin branched aerial roots, each pseudobulb with 2-4 stiff narrow leaves that are jointed with the basal sheath. The inflorescence, which branches towards the apex, has thin wiry stems and bears numerous small pale-coloured flowers in which the lateral sepals are fused together to form a narrow structure that projects beneath the labellum. The labellum is fixed by its base to the column base and then projects forwards. The column, which lacks a foot, has 2 unusual narrow projecting arms and a hood over the anther.
Clumping epiphytic orchids; roots thin, white, much-branched, extending aerially; pseudobulbs crowded, short and broad, with several nodes; leaves jointed to a basal sheath, confined to apical nodes, thin but leathery, longer than wide, flat; racemes or panicles from basal nodes, multiflowered; flowers lasting 2-4 days, small, opening sequentially; lateral sepals fused to form a synsepalum that subtends the labellum; petals spreading widely; labellum base fused with the column to form a pseudospur; lamina porrect, at right angles to the column, 3-lobed; column wings with 2 narrow porrect arms, the apex extending as a mitra over the anther; column without a foot.
Significant Generic Characters
A genus of about 12 species distributed in India, Malaysia, Philippines, Indonesia, New Guinea and Australia where there is a single endemic species distributed in northeastern Queensland between Cape York (10º41' S) and the Daintree River (about 16º12' S). State occurrence: Queensland.
Size and Distribution
The Australian species of Acriopsis grows on trees in lowland rainforest and swamp forest, often close to the coast but in some areas extending to low altitudes in the ranges.
Reproduction: Reproduction in Acriopsis is solely from seed. Seed dispersal takes 4-6 months after pollination and the capsule segments spread widely for seed dispersal. Apomixis is unknown in the genus.
Seasonal Growth: Acriopsis plants grow actively during the spring and summer months and are relatively quiescent for the remainder of the year.
Flowering: The native species flowers mainly in winter and spring.
Hybrids: Natural hybrids involving the native species of Acriopsis are unknown.
Fire: The native species of Acriopsis does not grow in fire-prone habitats.
Acriopsis, which is derived from the Greek akris, locust and -opsis, resemblance, refers to the unusual column that resembles the shape of a locust.
Perennial, evergreen, epiphytic, autotrophic, herbs, sympodial. Plants glabrous. Roots thin, extensively branched, mostly erect, aerial and litter-trapping, white. Rhizome very short, branched. Pseudobulbs well-developed, consisting of few nodes, crowded, hard, when young covered by white scarious bracts. Trichomes absent. Aerial growths absent. Leaves few from the upper nodes, sessile, articulated on the leaf base, longer than wide, thin textured but coriaceous, smooth, flat, grooved at the base; base sheathing the pseudobulb; margins entire; apex entire. Inflorescence racemose or paniculate, erect to arcuate, usually from a basal node, sometimes lateral, the peduncle and rhachis persistent long after seed dispersal, multiflowered. Peduncle thin, wiry, longer than the rhachis, with a few small scarious bracts. Floral bracts small, scarious, sheathing the base of the pedicel. Pedicel thin, merging with the ovary. Ovary short, straight, porrect from the pedicel. Flowers resupinate, small, stalked, lasting a few days, white, greenish or purplish (non-Australian). Perianth segments thin textured, entire, flat, straight. Dorsal sepal free, subsimilar to the synsepalum, straight; apex entire, cymbiform. Lateral sepals fused throughout to form a synsepalum that projects forwards beneath the labellum; apex entire. Petals free, subsimilar to the dorsal sepal, widely spreading; apex entire. Labellum complex, fixed to the column; markedly dissimilar in size and shape to the sepals and petals, ecalcarate. Labellum lamina complex; hypochile margins fused with the proximal part of the column to form a pseudospur; mesochile at right angles to the column; epichile 3-lobed; lateral lobes spreading; midlobe short, porrect; apex entire or cymbiform. Callus developed on the epichile, domed or notched. Nectar present. Spur absent. Column porrect from the end of the ovary, lacking free filament and style, fleshy, as long as the perianth segments, straight, with a short digitiform basal appendage. Column foot absent. Pseudospur present (see labellum lamina). Column wings well-developed, with 2 porrect lateral arms, the apex forming an extended mitra over the anther. Anther terminal, incumbent, narrow, 2-celled, persistent, smooth, erostrate or with a short rostrum; apex emarginate. Pollinarium present. Pollinia 2, slender, straight, laterally compressed, orange, hard, waxy, sessile. Stipe thin, long. Viscidium small. Rostellum well-developed, ventral, projecting between the arms of the column wings. Stigma ovate, concave. Capsules dehiscent, glabrous, the cells spreading widely at dehiscence; peduncle not elongated in fruit; pedicel not elongated in fruit. Seeds numerous, light coloured, winged.
Acriopsis is placed in its own subtribe, the Acriopsidinae Dressler.
The Australian species has at various times been included with overseas taxa including Acriopsis javanica Reinw. Ex Bl. and Acriopsis liliifolia (J.König) Ormerod. A detailed study involving cultivated plants from several countries shows that the native species is biologically and morphologically distinct and should be treated as an endemic species.
Clements, M.A. and Jones, D.L. (2002). Nomenclatural changes in the Dendrobieae (Orchidaceae) 1: the Australasian region. Orchadian 13(11): 485-497.
Dockrill, A.W. (1969). Australian Indigenous Orchids. Volume 1. The Society for Growing Australian Plants, Halstead Press, Sydney.
Dockrill, A.W. (1992). Australian Indigenous Orchids. Volume 1 & 2. Surrey Beatty & Sons in association with The Society for Growing Australian Plants, Chipping Norton, NSW.
Minderhoud, M.E. and de Vogel, E.F. (1986). A taxonomic revision of the genus Acriopsis Reinwardt ex Blume (Acriopsidinae, Orchidaceae). Orch. Monogr. 1: 1-16.