Epiphytes or lithophytes with very short indiscernible rhizomes anchored by thin roots that arise from nodes at the base of the canes. Pseudobulbs absent. Canes erect, porrect or pendulous, able to continue growth over 2-3 seasons, thin and wiry throughout, leafy. Leaves present at most nodes, arranged distichously, longer than wide, basally sheathing a node. Inflorescences emerging singly from a node opposite a leaf, breaking through its sheath, after flowering the supporting bracts break down leaving vestigial remnants. Flowers single, leaf-opposed, lasting a few days. Perianth segments thin to firm-textured. Lateral sepal bases fused with the column foot. Sepals similar in shape and size to each other. Petals much smaller than the sepals. Labellum firmly attached to the apex of the column foot. Labellum lamina prominently lobed, thick and fleshy, generally plain and unadorned.
Significant Generic Characters
Epiphytic/lithophytic orchids; stems cane-like, thin, growing over 2-3 seasons, leafy; leaves lasting several seasons, distichous, longer than wide, basally sheathing a node; floral nodes flowering once; inflorescence leaf-opposed, short; floral bracts not persistent; flowers single, lasting a few days; lateral sepal bases fused with the column foot; sepals similar in shape and size; petals much smaller than the sepals; labellum firmly attached to the apex of the column foot; lamina lobed, fleshy, generally unadorned.
Size and Distribution
A genus of about 30 species with its main occurrence in New Guinea, but also distributed in Indonesia, New Caledonia, Fiji and north-eastern Queensland where there is a single endemic species. State occurrence: Queensland.
Ecology
Species of Monanthos grow on trees and rocks in situations of moderate light where the humidity is relatively high and there is unimpeded air movement. 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 species of Monanthos usually last 3-5 days. Most species seem to be insect-pollinated but the vectors are unknown. Some species from New Guinea and Oceanic islands are known to be autogamous and may even be cleistogamous.
Reproduction: Reproduction in Monanthos is solely from seed. Seed dispersal takes 4-6 months after pollination and the capsules develop in a porrect to 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: Plants flower at intervals during the warm months of the year. Massed flowering and synchronous flowering do not occur in this genus.
Hybrids: Natural hybrids involving species of Monanthos are unknown.
Derivation
Monanthos refers to the single-flowered inflorescence.
Botanical Description
Perennial, evergreen, epiphytic or lithophytic herbs, sympodial. Roots elongate, thin, produced from nodes on the base of the canes. Rhizome superficial, branched. Pseudobulbs absent, the stems cane-like, crowded, thin, terete, capable of growth over two to three seasons, erect, porrect or pendulous, when young covered by scarious bracts. Trichomes absent from vegetative parts. Aerial growths absent or produced occasionally from the upper nodes. Leaves lasting several seasons, distichous, sessile, much longer than wide, firm-textured, smooth, not grooved or channelled; base sheathing, the sheath completely enclosing a node; margins entire; apex unequally emarginate. Inflorescence short, porrect, arising from a node opposite a leaf and breaking through its sheath, one-flowered. Floral nodes capable of producing a single inflorescence only. Peduncle very short, with a group of imbricate scarious bracts. Floral bracts scarious, tiny, barely subtending the base of the pedicel. Pedicel short, thin, merging with the ovary. Ovary short, straight, merging with the pedicel. Flowers resupinate, stalked, usually lasting a few days, white, green or yellow. Perianth segments thin to firm-textured, incurved to widely spreading, entire. Dorsal sepal free, subsimilar to the lateral sepals; apex entire. Lateral sepals subsimilar to the dorsal sepal, attached by their bases to the column foot; apex entire. Petals free, smaller and a different shape to the sepals; apex entire. Labellum continuous with the apex of the column foot, markedly dissimilar in size and shape to the sepals and petals, ecalcarate. Labellum lamina thick and fleshy, three-lobed; lateral lobes entire; midlobe short, unadorned; margins entire; apex entire. Spur absent. Callus vestigial. Nectar absent. Column lacking free filament and style, fleshy, much shorter than the perianth segments, nearly straight; ventral surface smooth. Column wings present, reduced, ventral and with short tooth-like apical stelidia. Column foot well developed, longer than the column, straight or curved. Pseudospur absent. Anther terminal, incumbent, 2-celled, persistent, attached dorsally by a ligulate claw, erostrate, smooth or papillate; apex smooth. Pollinarium absent. Pollinia 4 in 2 pairs, straight or falcate, orange, hard, waxy. Viscidium absent. Rostellum ventral, swollen, transverse, either deeply notched or paired. Stigma entire, transverse, concave. Capsules dehiscent, nearly as wide as long, glabrous, pendulous; peduncle not elongated in fruit; pedicel not elongated in fruit. Seeds numerous, relatively large, light coloured, winged.
Taxonomy
Monanthos was until recently treated as a section within Dendrobium (Brieger 1981).
Nomenclature
Monanthos (Schltr.) Brieger in . 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) Schltr., Die Orchideen 3(1): 659 (1981); Dendrobium section Monanthus Schltr., Fedde Rep. Beih. 1: 451 (1912); Dendrobium section Biloba J.J.Sm., Orch. Amboin. 69 (1905).
Type species: Dendrobium bilobum Lindl. [Monanthos biloba (Lindl.) Brieger].
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): 485-497.
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.