Tangle Orchids
Erect to pendulous epiphytes or lithophytes (rarely terrestrial) with numerous relatively thin roots (often growing through the air) and thin fibrous leafy stems, the relatively small, crowded or spaced thin leaves arranged in 2 ranks. Inflorescences are relatively short and unbranched and the small uncrowded flowers are often fragrant. They have relatively narrow incurved to spreading segments and a stiffly attached deeply spurred labellum with a thin or clubbed internal hairy structure. The column is short with a short to long column foot.
Similar Genera
Significant Generic Characters
Epiphytic/lithophytic (rarely terrestrial) orchids; plants small to large, erect to pendulous, sometimes dangling from a few roots; stems thin, fibrous; leaves crowded or well-spaced, in 2 ranks, much longer than wide, thin to thick-textured, leathery, unequally notched; flowers small, lasting several days; perianth segments thin to thick-textured; sepals subsimilar; petals subsimilar to the sepals; labellum firmly attached to the apex of the column foot; lamina 3-lobed, pouched, with a basal spur; labellum spur containing a single narrow finger-like or clubbed hairy callus structure attached to the ventral surface near the opening of the spur and extending backwards into the spur; column short, with a short foot; pollinia 4, sessile, in 2 unequal pairs.
Size and Distribution
A genus of 3 species, 2 of which, Plectorrhiza brevilabris and P. tridentata, are endemic on mainland Australia and the other, P. erecta, is endemic on Lord Howe Island. On the mainland Plectorrhiza is distributed between the McIlwraith Range (about 13º30' S) on Cape York Peninsula, Queensland, and to the east of the Snowy River in far eastern Victoria (about 37º50' S). State occurrence: Queensland, New South Wales (including Lord Howe Island), Victoria.
Ecology
Plectorrhiza brevilabris and P. tridentata grow on shrubs and trees in rainforest, streamside vegetation and wetter types of open forest. In temperate and subtropical regions they are mainly found at low to moderate altitudes but in the tropics they are restricted to moderate or high altitudes in the ranges and tablelands. Occasional plants are found growing on rocks. By contrast P. erecta mainly grows as a terrestrial in sandy soil, usually among low shrubs, with the roots growing in the surface litter and on the bark of the shrubs.
Biology
Pollination: The flowers of Plectorrhiza species last many days and are pollinated by native bees.
Reproduction: Reproduction in Plectorrhiza is solely from seed. Seed dispersal takes 10-12 months after pollination and the capsules develop in a porrect or pendulous position. Apomixis is unknown in the genus.
Seasonal Growth: Plants of Plectorrhiza species grow mainly during the spring and summer months and are relatively quiescent for the remainder of the year.
Flowering: Plectorrhiza species flower in spring and early summer.
Hybrids: Natural hybrids involving species of Plectorrhiza are unknown.
Derivation
Plectorrhiza, which is derived from the Greek plectos, plaited, twisted and rhizos, root, refers to the tangled roots which are prominent in the mainland species.
Botanical Description
Perennial, evergreen, epiphytic, lithophytic or terrestrial herbs, monopodial. Roots thick, elongate, straight or convolute, adherent or aerial. Plants small to moderately large, erect, porrect or pendulous, sometimes dangling and attached to the host by a few roots. Stem relatively thick, short to moderately long, fibrous, sparsely branched. Pseudobulbs absent. Trichomes present on labellum callus. Leaves lasting several seasons, distichous, sessile, longer than wide, mostly flat, thin to thick, coriaceous, smooth; base sheathing the stem, usually persistent after leaf abscission; margins entire; apex unequally emarginate. Inflorescence lateral, racemose, erect, arcuate or pendulous, multiflowered. Peduncle shorter or longer than the rhachis, wiry, with few imbricate scarious bracts. Rhachis straight. Floral bracts scarious, sheathing the base of the ovary or pedicel. Pedicel (if present) short, thin, merging with the ovary. Ovary short, mostly straight. Flowers resupinate, relatively small, stalked or sessile, opening sequentially, lasting several days, brownish, white, green or yellow, fragrant. Perianth segments moderately thick-textured, incurved or spreading. Dorsal sepal free, subsimilar to the lateral sepals. Lateral sepals free, subsimilar to the dorsal sepal, flanking the labellum. Petals free, subsimilar to the sepals. Labellum stiffly attached to the apex of the column foot, markedly dissimilar in size and shape to the sepals and petals, calcarate. Labellum lamina fleshy, with a basal spur, 3-lobed; spur shallowly to deeply saccate, cylindric, straight or curved, with a narrow or clavate hairy callus structure projecting towards the base of the spur; lateral lobes short, blunt or pointed; midlobe short, porrect to recurved, thick, fleshy. Spur (see labellum). Callus (see labellum spur). Nectar present. Column short, porrect from the apex of the ovary, lacking free filament and style, fleshy, nearly straight. Column wings absent. Column foot present, short. Pseudospur absent. Anther terminal, incumbent, 2-celled, persistent, smooth, with a narrow elongate curved rostrum. Pollinarium present. Pollinia 4 in 2 appressed pairs, unequal, orange, hard, waxy, sessile. Stipe well-developed, long, narrow. Viscidium present, small, narrow Rostellum ventral, elongate, bifid. Stigma entire, concave. Capsules dehiscent, glabrous, porrect; peduncle not elongated in fruit; pedicel not elongated in fruit. Seeds numerous, light coloured, winged.
Taxonomy
Within the Vandeae, Plectorrhiza is characterised by 3-lobed labellum; labellum spur containing a single narrow finger-like or clubbed hairy callus structure attached to the ventral surface near the opening of the spur and extending backwards into the spur; column short, with a short foot and, 4 sessile pollinia in 2 unequal pairs.
Nomenclature
Plectorrhiza Dockr. Austral. Sarcanth. 27 (1967).
Type species: Plectorrhiza tridentata (Lindl.) Dockr. [Cleisostoma tridentatum Lindl.].
Infrageneric Taxa: No infrageneric taxa are currently recognised.
References
Dockrill, A.W. (1967). Australasian Sarcanthinae. The Australasian Native Orchid Society, Sydney.
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.