Rock Orchids
Epiphytes or lithophytes with very short almost indiscernible rhizomes anchored by roots which arise from nodes at the base of the pseudobulb. The hard pseudobulbs range from being short and broad to elongated, usually swollen at the base, but sometimes of uniform thickness. The leaves, which are confined to the apical region of the pseudobulbs, are thick and fleshy, longer than wide, flat, basally sheathing and with an entire or unequally notched apex. The flowers are borne on short to long racemes that arise from the upper nodes of a pseudobulb. Each flower, which is long-lasting, is relatively large, thick-textured and often scented. The perianth segments are flat and the bases of the lateral sepals are fused with the column foot. The petals are generally shorter than the sepals. The labellum, which is distinctly three-lobed, is relatively thin textured, with prominent central ridges. It is stiffly attached to the apex of the column foot.
Significant Generic Characters
Epiphytic/lithophytic orchids; rhizomes almost indiscernible; pseudobulbs range from short and broad to elongated, multinoded, usually basally swollen, sometimes uniform throughout; leaves, confined to apical nodes, thick and fleshy, longer than wide, flat, basally sheathing; racemes from distal nodes, multiflowered; flowers long-lasting, relatively large, thick-textured, often scented; perianth segments flat; lateral sepal bases fused with the column foot; petals generally shorter than the sepals; labellum stiffly attached to the apex of the column foot, three-lobed; callus with prominent central ridges.
Size and Distribution
A genus of about 20 species distributed mainly in Australia with a few species occurring in New Caledonia and on Norfolk Island and Lord Howe Island. The Australian species are restricted to the eastern states and are found between Cape York (10º41' S) and eastern Victoria at about 37º34' S. State occurrence: Queensland, New South Wales (including Lord Howe and Norfolk Islands), Victoria.
Ecology
The Australian species of Thelychiton are widely distributed on the east coast and range from lowland situations (Thelychiton speciosus frequently grows on coastal headlands) to more than 1100 m alt. Species variously occur in tropical, subtropical and temperate regions. They grow on trees and rocks in situations of bright light to shade, fluctuating humidity and free air movement. Habitats include rainforest, open forest, woodland, swamp forest, coastal scrubs, mangroves and rocky outcrops and escarpments. The climate where species of Thelychiton grow varies from tropical to subtropical and temperate. In the tropics the majority of rain falls during the summer wet season (December to March), the remaining months being much drier and having sporadic or intermittent rain.
Biology
Pollination: The flowers of species of Thelychiton last many days and are pollinated by native bees. The flowers of Thelychiton brachypus and T. macropus, both from Norfolk Island, are autogamus and sometimes also cleistogamous.
Reproduction: Reproduction in Thelychiton is mainly from seed, although some species, such as T. fleckeri and T. finniganensis, produce numerous aerial growths that can act as a localised form of clonal colonisation. Seed dispersal takes 4-6 months after pollination and the capsules develop in a pendulous position. Apomixis is unknown in the genus.
Seasonal Growth: Thelychiton plants grow actively during the spring and summer months and are relatively quiescent for the remainder of the year.
Flowering: Flowering occurs mainly in spring.
Hybrids: Natural hybrids involving species of Thelychiton are relatively uncommon but several have been formally described (example Thelychiton suffusus is a named natural hybrid between T. kingianus and T. gracilicaule). Intergeneric hybrids are unknown or extremely rare (possible example Tetrabaculum tetragonum x Thelychiton kingianus).
Derivation
Thelychiton, which is derived from the Greek thelys, female and chiton, dress, refers to the column hooding the stigma.
Botanical Description
Perennial, evergreen, epiphytic or lithophytic herbs, sympodial. Plants glabrous. Roots elongate, branched, produced from nodes on the base of the pseudobulb. Rhizome superficial, branched. Pseudobulbs well-developed, multinoded, crowded, hard, elongate, either swollen at the base or nearly cylindrical, when young covered by scarious bracts. Trichomes absent. Aerial growths present or absent, arising from apical nodes on the pseudobulbs. Leaves distichous, arising from apical nodes, sessile, longer than wide, thin textured to thick and fleshy, coriaceous, smooth, flat, not grooved or channelled; base sheathing the pseudobulb; margins entire; apex entire or unequally emarginate. Inflorescence racemose, erect to arcuate, arising from an apical or subapical node on a mature pseudobulb, multiflowered. Peduncle shorter or longer than the rhachis, sometimes much reduced, the base covered with imbricate scarious bracts. Floral bracts scarious, sheathing the base of the pedicel. Pedicel relatively short to long, thin, merging with the ovary. Ovary short, straight, porrect from the pedicel or at an angle. Flowers resupinate, stalked, lasting many days, white, yellow, orange or pink, often strongly scented; labellum with distinct striae. Perianth segments thin to thick-textured, widely spreading, entire, flat, straight. Dorsal sepal free, subsimilar to the lateral sepals, straight; apex entire, flat. Lateral sepals subsimilar to the dorsal sepal, falcate, attached by their bases to the column foot; apex entire. Petals free, shorter than the sepals or subsimilar; 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 oblong, relatively thin-textured, strongly three-lobed; lateral lobes relatively large, erect, flanking the column or incurved, entire; mid-lobe short, porrect to recurved; apex entire or apiculate. Callus consisting of narrow median parallel ridges. Nectar absent. Spur absent. Column lacking free filament and style, fleshy, shorter than the perianth segments, nearly straight. Column foot well developed, as long as the column, straight or curved. Pseudospur absent. Column wings present, reduced, ventral and with short tooth-like apical stelidia. 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
Thelychiton was originally included in Dendrobium but can be immediately be distinguished by the thickened pseudobulbs, leaves lasting many seasons and confined to the upper nodes, inflorescences arising from apical and subapical nodes and the labellum distinctly 3-lobed.
Nomenclature
Thelychiton Endl., Prod. Fl. Norf. 32 (1833). Type species: Thelychiton macropus Endl.
Dendrocoryne Brieger in Schltr., Die Orchideen 3(1): 724 (1981). Type species: Dendrobium speciosum Sm.
Infrageneric taxa: No infrageneric taxa are currently recognised.
References
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.