A small genus, endemic to Australia, with four species of epiphytic or lithophytic orchids. They have very short almost indiscernible rhizomes or prominent creeping rhizomes, anchored by roots from the pseudobulb base. The pseudobulbs are hard, relatively short and broad, tapering from the base. There are one to three leaves per pseudobulb growing from the apex. The tough, flat leaves are larger than wide with an unusually notched apex. The inflorescence is small and thin, with multiple individually stalked flowers. The small flowers, 0.7-1.5 cm in width, last several days, are white, yellow or orange in colour and often scented. The bases of the lateral sepal are partly fused with the column foot. The petals are similar to or smaller than the sepals. The labellum is stiffly attached to the apex of the column foot. Australorchis flower in autumn and spring, occurring in Queensland and northern New South Wales.
Significant Generic Characters
Epiphytic/lithophytic orchids; rhizomes very short or creeping; pseudobulbs relatively short, broad, tapered from the base, multi-noded; leaves lasting several seasons, 1-2 per pseudobulb, apical, thin-textured but tough, longer than wide, flat; racemes arising from the apical node of a pseudobulb, relatively short, multi-flowered; flowers lasting several days, relatively small; perianth segments flat; lateral sepal bases partly fused with each other and with the column foot; petals subsimilar to or smaller than the sepals; labellum stiffly attached to the apex of the column foot; lamina either distinctly three-lobed or the midlobe reduced and vestigial, thin to thick-textured; callus with prominent central ridges.
Size and Distribution
This genus, which is endemic to Australia, consists of 4 species restricted to the eastern states. They are found between Mt Finnigan south of Cooktown, Queensland (15º48' S) and near Grafton (29º43' S) in northeastern NSW. State occurrence: Queensland, New South Wales.
Ecology
Species of Australorchis are distributed on the east coast from the lowlands to more than 1100 m alt. Three species occur in the tropics with one extending into the subtropics where there is an additional species. They grow on trees and rocks in situations of bright light, fluctuating humidity and free air movement. Habitats include rainforest, open forest, woodland, coastal scrubs and rocky escarpments. The climate where species of Australorchis grow varies from tropical to subtropical. In the tropics the majority of rain falls during the summer wet season (December to March) with the remaining months being much drier and having sporadic or intermittent rain.
Biology
Pollination: The flowers of species of Australorchis last several days, are often fragrant and are pollinated by small native bees.
Reproduction: Reproduction in Australorchis is solely from seed. Seed dispersal takes 4-6 months after pollination and the capsules develop in a pendulous position. Apomixis is unknown in the genus.
Seasonal Growth: The plants grow actively during the spring and summer months and are relatively quiescent for the remainder of the year.
Flowering: Flowering occurs in autumn and spring.
Hybrids: Natural hybrids involving species of Australorchis are unknown. Australorchis is not known to participate in natural intergeneric hybridisation.
Derivation
Australorchis is derived from the Latin australis, southern and Orchis, another genus of orchid, and also used as a general term for orchid; it literally means "southern orchid".
Botanical Description
Perennial, evergreen, epiphytic or lithophytic herbs, sympodial. Plants glabrous. Roots elongate, branched, produced from nodes on the base of the pseudobulb. Rhizome variable, from superficial (Australorchis eungellensis, Australorchis schneiderae) to well-developed and creeping (Australorchis carrii, Australorchis monophylla), branched. Pseudobulbs well-developed, either crowded (Australorchis eungellensis, Australorchis schneiderae) or widely-spaced (Australorchis carrii, Australorchis monophylla), hard, short to relatively elongate, mostly ovoid, when young covered by scarious bracts. Trichomes absent. Aerial growths absent. Leaves lasting several seasons, solitary or in pairs, sessile, longer than wide, firm textured, coriaceous, smooth, flat, not grooved or channelled; base not sheathing the pseudobulb; margins entire; apex unequally emarginate. Inflorescence racemose, erect to arcuate, arising from the apical node on a mature pseudobulb, multi-flowered. Peduncle shorter than the rhachis, the base covered with imbricate scarious bracts. Floral bracts scarious, sheathing the base of the pedicel. Pedicel relatively short, thin, merging with the ovary. Ovary short, straight, porrect from the pedicel. Flowers resupinate, stalked, lasting several days, white, yellow or orange, often scented; labellum with or without contrasting colours and/or markings. Perianth segments thin to thick-textured, incurved to widely spreading, entire, flat. Dorsal sepal free, subsimilar to the lateral sepals, straight; apex entire, flat. Lateral sepals subsimilar to the dorsal sepal, straight or falcate, attached by their bases to the column foot; apex entire. Petals free, subsimilar or shorter than the sepals; apex entire. Labellum stiffly attached to the apex of the column foot, markedly dissimilar in size and shape to the sepals and petals, ecalcarate. Labellum lamina more or less elliptic to oblong, relatively thin-to thick-textured, strongly three-lobed or the midlobe vestigial (Australorchis schneiderae); lateral lobes relatively large, erect, flanking the column or incurved, entire; midlobe well-developed or vestigial, recurved; apex entire or apiculate. Spur absent. Callus consisting of either narrow, median, parallel ridges or a large central plate. Nectar absent. Column lacking free filament and style, fleshy, shorter than the perianth segments, nearly straight. Column wings present, reduced, ventral and with short tooth-like apical stelidia. Column foot well developed, longer than the column, curved. Pseudospur present, formed by the union of the anterior basal margin of the lateral sepals and the bases of the lateral sepals with the margins of the column foot. Anther terminal, incumbent, 2-celled, persistent, attached dorsally by a ligulate claw, smooth, erostrate or with a short rostrum; apex smooth. Pollinarium absent. Pollinia 4 in 2 pairs, straight or falcate, yellow or orange, hard, waxy. Viscidium absent. Rostellum ventral, swollen, transverse. Stigma entire, vertical, concave. Capsules dehiscent, glabrous, pendulous; peduncle not elongated in fruit; pedicel not elongated in fruit. Seeds numerous, light coloured, winged.
Taxonomy
Australorchis is a relatively recent segregate from Dendrobium (Brieger 1981).
Nomenclature
Australorchis Brieg., Die Orchideen 3(1): 741 (1981); Dendrobium section Australorchis (Brieg.) Dockrill, Australian Indigenous Orchids 1: 439 (1992). Type species: Dendrobium monophyllum F.Muell. [Australorchis monophylla (F.Muell.) Brieg.].
Infrageneric Taxa: No infrageneric taxa are currently recognised.
References
Brieger, F.G. (1981). Subtribus Dendrobiinae. In F.G. Brieger, R. Maatsch and K. Senghas (eds), Rudolph Schlechter, Die Orchideen: ihre Bescreibung, Kultur und Züchtung, 3rd edn, Band 1, Teil A, Lieferung 11-12 (Paul Parey: Berlin and Hamburg).
Clements, M.A. and Jones, D.L. (2002). Nomenclatural changes in the Dendrobieae (Orchidaceae). 1: The Australasian Region. Orchadian 13(11): 485-492.
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.