Leioanthum bifalce

Bee Orchids

Epiphytes or lithophytes anchored by roots that arise from nodes at the base of the pseudobulb. Rhizomes very short, indiscernible. Pseudobulbs hard, elongated, thin at the base, thickened in the distal part. Leaves restricted to the apical nodes, longer than wide, flat or shallowly concave, without any channel or groove, not sheathing basally, apex unequally notched. Racemes from apical nodes, long; peduncle much longer than the rhachis; flowers crowded at the end. Flowers long-lasting, firm- to thick-textured. Perianth segments flat, relatively broad. Sepals dissimilar. Bases of lateral sepals fused with the column foot. Petals narrower than the sepals. Labellum stiffly attached to the apex of the column foot. Labellum lamina distinctly three-lobed; lateral lobes long, narrow; midlobe broad, notched. Callus with prominent central, deeply grooved papillate ridge.

Significant Generic Characters

Epiphytic/lithophytic orchids; rhizomes indiscernible; pseudobulbs hard, elongated, thin basally, thickened distally; leaves lasting several seasons, restricted to apical nodes, longer than wide, flat, not sheathing basally; racemes from apical nodes; peduncle much longer than rhachis; flowers restricted to the apex, crowded, long-lasting; perianth segments flat, relatively broad; sepals dissimilar; lateral sepal bases fused with the column foot; petals narrower than the sepals; labellum stiffly attached to the apex of the column foot; lamina three-lobed; lateral lobes long, narrow; midlobe broad, notched; callus with a deeply grooved papillate ridge.

Size and Distribution

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distribution map

A genus of about 4 species distributed in Indonesia, New Guinea and northeastern Queensland where there is a single non-endemic species. The Australian species, Leioanthum bifalce, is widely distributed in New Guinea and in Australia occurs in some islands of Torres Strait and sporadically from Cape York (1041' S) to the Daintree River (1617' S). State occurrence: Queensland (including Moa and Dauan Islands).

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Ecology

Leioanthum bifalce grows in strong light in humid but airy situations on large boulders, cliff faces and the trunks and branches of rainforest trees. The climate is tropical and the majority of rain falls during the summer wet season (December to March), with the remaining months much drier and having sporadic or intermittent rain, particularly localised coastal showers.

Biology

Pollination: The flowers of Leioanthum bifalce, which last several days, are insect-pollinated. Wasps have been observed visiting the flowers.

Reproduction: Reproduction in Leioanthum bifalce is solely from seed. Seed dispersal takes 8-10 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 winter.

Hybrids: Natural hybrids involving Leioanthum bifalce in Australia are unknown.

Derivation

Leioanthum, which is derived from the Greek leios, smooth and anthos, flower, refers to the smooth flowers that contrast with the hairy flowers of Sayeria.

Botanical Description

Perennial, evergreen, epiphytic or lithophytic herbs, sympodial. Plants glabrous. Roots elongate, produced from nodes on the base of the pseudobulb. Rhizome superficial, branched. Pseudobulbs well-developed, crowded, hard, elongate, thin at the base, thickened distally, when young covered by scarious bracts. Trichomes absent. Aerial growths absent. Leaves lasting several seasons, distichous, restricted to apical nodes, sessile, much longer than wide, thick-textured, coriaceous, smooth, not grooved or channelled; base not sheathing the pseudobulb; margins entire; apex unequally emarginate. Inflorescence racemose, erect, arising from an apical node on a mature pseudobulb, few-flowered. Peduncle much longer than the rhachis, with scattered scarious bracts.  Floral bracts scarious, small, subtending the base of the pedicel. Pedicel long, thin, merging with the ovary. Ovary short, straight. Flowers resupinate, stalked, lasting several days, green, yellowish or brownish; labellum with purplish markings. Perianth segments firm- to thick-textured, widely spreading, entire, straight. Dorsal sepal free, smaller than the lateral sepals; apex entire, flat.  Lateral sepals larger than the dorsal sepal, relatively broad, attached by their bases to the column foot; apex entire. Petals free, narrower than the sepals, about as long as the dorsal sepal; 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, fleshy, strongly three-lobed; lateral lobes moderately long, erect, flanking the column, entire; midlobe broad, porrect to recurved; apex deeply notched, the lobes flat. Spur absent. Callus consisting of a deeply grooved ridge, papillate distally, with a notched apex. Nectar absent. Column lacking free filament and style, fleshy, much shorter than the perianth segments, nearly straight. Column wings present, reduced, ventral and with short tooth-like apical stelidia. Column foot well developed, much longer than the column, at right angles to the column, straight or curved. Pseudospur absent. Anther terminal, incumbent, 2-celled, persistent, attached dorsally by a ligulate claw, smooth, shortly rostrate; 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, transverse, concave. Capsules dehiscent, large, glabrous, pendulous; peduncle not elongated in fruit; pedicel not elongated in fruit. Seeds numerous, relatively large, light coloured, winged.

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Taxonomy

Leioanthum is a recent segregate from Dendrobium (Jones and Clements 2002).

Nomenclature

Leioanthum M.A.Clem. and D.L.Jones, Orchadian 13(11): 490 (2002). Type species: Dendrobium bifalce Lindl. [Leioanthum bifalce (Lindl.) M.A.Clem. and D.L.Jones].

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.

Schlechter, R. (1982). The Orchidaceae of German New Guinea (English translation by R.S. Rogers, H.J. Katz and J.T. Simmons). Australian Orchid Foundation, Melbourne.