Erect to pendulous epiphytes with numerous roots (often growing through the air) and relatively long thin fibrous leafy stems, the relatively small, thin well-spaced leaves being arranged in 2 ranks and with distinctively hooked tips. Inflorescences are relatively short and unbranched and the small uncrowded flowers are fragrant. They have relatively broad spreading segments and a fleshy labellum that is hinged to the apex of the column foot. The column is short with a relatively long column foot.
Significant Generic Characters
Epiphytic orchids; plants small to moderately large, erect to pendulous, sometimes dangling from a few roots; stems thin, fibrous; leaves well-spaced, in 2 ranks, much longer than wide, thin-textured, leathery; apex hooked, unequally notched; inflorescence racemose; flowers small, lasting several days; perianth segments thin-textured, spreading; sepals subsimilar; petals smaller than the sepals; labellum hinged to the apex of the column foot; lamina 3-lobed, without a spur; lateral lobes erect; midlobe long, narrow, fleshy; column short, with a long foot; pollinia 4, stalked on a stipe, in 2 subequal pairs.
Size and Distribution
A monospecific genus with the single species, Mobilabium hamatum, endemic in eastern Australia and distributed between the Big Tableland (about 15º45' S) near Cooktown and the Paluma Range (about 19º10' S) near Townsville in northeastern Queensland. State occurrence: Queensland.
Ecology
Mobilabium hamatum grows at moderate to high altitudes on shrubs and trees in rainforest, streamside vegetation and wetter types of open forest.
Biology
Pollination: The flowers of Mobilabium hamatum last many days, contain nectar and are probably pollinated by native bees.
Reproduction: Reproduction in Mobilabium hamatum is solely from seed. Seed dispersal takes 10-12 months after pollination and the capsules develop in a porrect position. Apomixis is unknown in the genus.
Seasonal Growth: Plants of Mobilabium hamatum grow mainly during the spring and summer months and are relatively quiescent for the remainder of the year.
Flowering: Mobilabium hamatum flowers in winter and early spring.
Hybrids: Natural hybrids involving Mobilabium hamatum are unknown.
Derivation
Mobilabium, which is derived from the Latin mobilis, mobile and labium, lip, refers to the hinged labellum.
Botanical Description
Perennial, evergreen, epiphytic herbs, monopodial. Roots relatively thick, elongate, straight or convolute, adherent or aerial. Plants small to moderately large, erect or dangling. Stem relatively thin, short to moderately long, fibrous, sparsely branched. Pseudobulbs absent. Trichomes absent. Leaves lasting several seasons, well-spaced, distichous, sessile, longer than wide, mostly flat, thin to thick, coriaceous, smooth; base sheathing the stem, usually persistent after leaf abscission; margins entire; apex uncinate, unequally emarginate. Inflorescence lateral, racemose, porrect to arcuate, multiflowered. Peduncle shorter than the rhachis, wiry, with basal imbricate scarious bracts. Rhachis straight. Floral bracts scarious, sheathing the base of the pedicel. Pedicel short, thin, merging with the ovary. Ovary short, shallowly curved. Flowers resupinate, relatively small, stalked or sessile, opening sequentially, lasting several days, cream or greenish with reddish markings, fragrant. Perianth segments thin-textured, spreading. Dorsal sepal free, subsimilar to the lateral sepals. Lateral sepals free, subsimilar to the dorsal sepal, flanking the labellum base. Petals free, smaller than the sepals. Labellum hinged to the apex of the column foot, markedly dissimilar in size and shape to the sepals and petals, ecalcarate. Labellum lamina fleshy, 3-lobed; lateral lobes relatively large, erect, pointed; midlobe prominent, calceiform, thick, fleshy. Spur absent. Callus consting of an erect, incurved fleshy structure. Nectar present, sticky. Column short, porrect from the apex of the ovary, lacking free filament and style, fleshy, shallowly curved. Column wings obscure, ventral. Column foot long, at right angles to the column. Pseudospur absent. Anther terminal, incumbent, 2-celled, persistent, smooth, with a narrow curved rostrum. Pollinarium present. Pollinia 4 in 2 appressed pairs, subequal, orange, hard, waxy, stalked. Stipe well-developed, short, relatively broad. Viscidium present, large, broad. Rostellum ventral, broad, 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, Mobilabium is characterised by hooked leaf tips; hinged, 3-lobed labellum; solid fleshy labellum midlobe with a fleshy incurved callus structure; column short, with a long foot and, 4 stalked pollinia in 2 subequal pairs.
Nomenclature
Mobilabium Rupp, North Queensland Naturalist. 13(78): 2-4, fig. (1946). Type species: Mobilabium hamatum Rupp.
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.