Epiphytic or lithophytic orchids with very short to indiscernible rhizomes anchored by roots arising from basal nodes. Pseudobulbs porrect to pendulous, hard, cane-like, elongated, either cylindrical or thickened towards the apex. Leaves lasting one season, scattered along the pseudobulb, longer than wide, flat, without any channel or groove, basally sheathing, with an unequally notched apex. Racemes short, few-flowered, arising from the middle to upper nodes of a pseudobulb. Flowers lasting several days, thin to firm-textured. Perianth segments flat. Lateral sepal bases fused with the column foot. Petals of similar width to the sepals. Labellum firmly attached and continuous with the apex of the column foot. Labellum lamina unlobed, tubular at the base, distinctly flared towards the apex, the ventral surface adorned with small bristles or papillae, with a prominent basal pseudospur.
Significant Generic Characters
Epiphytic/lithophytic orchids: pseudobulbs hard, cane-like, elongated; leaves lasting one season, distichous, planar; racemes from lateral nodes, short, few-flowered; flowers lasting several days; perianth segments flat; lateral sepal bases fused with the column foot; petals of similar width to the sepals; labellum continuous with the apex of the column foot; lamina unlobed, tubular proximally, flared distally, adorned with small bristles or papillae; pseudospur prominent; column foot with a sunken apical area.
Size and Distribution
A genus of about 50 species distributed in China, Japan, Taiwan, South Korea, India, Thailand, Mianmar, Malaysia, Philippines, Indonesia, Vanuatu, Solomon Islands, New Guinea and north-eastern Queensland where there is a single endemic species. The Australian species, Dendrobium stuartii, is restricted to northern parts of Cape York Peninsula. State occurrence: Queensland.
Ecology
Dendrobium stuartii occurs on ridges and slopes growing on rocks and the trunks and branches of rough-barked or flaky-barked trees in rainforest. Plants usually occur in situations of bright light and with free 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 Dendrobium stuartii are short-lived and self-pollinating.
Reproduction: Reproduction in Dendrobium stuartii is solely from seed. Seed dispersal takes 4-6 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 summer.
Hybrids: Natural hybrids involving Dendrobium stuartii in Australia are unknown.
Derivation
Dendrobium, which is derived from the Greek dendros, tree and bios, life, refers to the epiphytic habit of most species.
Botanical Description
Perennial, deciduous, epilithic herbs, sympodial. Roots elongate, produced from nodes on the base of the pseudobulb. Rhizome superficial, branched. Pseudobulbs well-developed, crowded, hard, elongate, cylindrical or thickened towards the apex, when young covered by scarious bracts. Trichomes absent. Aerial growths produced from the upper nodes. Leaves lasting one season, distichously arranged along the pseudobulb, sessile, much longer than wide, thin-textured to moderately thick, smooth, not grooved or channelled; base sheathing the pseudobulb; margins entire; apex unequally emarginate. Inflorescence racemose, short, porrect to arcuate, arising from the middle and upper nodes on a mature pseudobulb, few-flowered (usually 1-5 flowers). Peduncle very short, the base with imbricate scarious bracts. Floral bracts scarious, small, subtending the base of the pedicel. Pedicel relatively long, thin, merging with the ovary. Ovary short, straight or curved. Flowers resupinate, stalked, lasting several days, white, green, yellow, pink, mauve and purple, often with contrasting colours in the labellum. Perianth segments thin to firm-textured, widely spreading, entire. Dorsal sepal free, subsimilar to the lateral sepals; apex entire, flat. Lateral sepals subsimilar to the dorsal sepal, attached by their bases to the column foot; apex entire. Petals free, similar 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, calcarate. Labellum lamina more or less obovate, thin to fleshy, unlobed; basal part tubular, flanking the column, entire; distal part expanded or flared; margins setose to fimbriate; apex entire or apiculate. Spur absent. Callus consisting of narrow parallel ridges, with or without setulose bristles and papillae. 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, as long as the column, straight or curved, often with a sunken apical area. Pseudospur formed by the elongated base of the labellum and column foot. Anther terminal, incumbent, 2-celled, persistent, attached dorsally by a ligulate claw, often verrucose, erostrate; apex smooth. Pollinarium absent. Pollinia 4 in 2 pairs, straight or falcate, yellow, 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.
Taxonomy
Dendrobium has generally been treated as a large polymorphic genus but a broad taxonomic study (Brieger 1981) and recent phylogenetic studies based on chloroplast DNA (Yukawa et al. 1993, 1996, 2000, Yukawa and Uehara 1996) and nuclear DNA (Clements and Jones 2002, Clements 2003) have challenged that view. Dendrobium is yet to be defined in the strict sense but its main distinguishing characters are detailed in this treatment.
Nomenclature
Dendrobium Sw., Nov. Act. Soc. Sci. Upsal. 6: 82 (1799) (nom. cons.). Type species: Dendrobium moniliforme Sw.
Infrageneric Taxa: The status of infrageneric taxa within Dendrobium sens. str. is currently being assessed.
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. (2003). Molecular phylogenetic systematics in the Dendrobiinae (Orchidaceae), with emphasis on Dendrobium section Pedilonum. Telopea 10(1): 147-198.
Clements, M.A. and Jones, D.L. (2002). Nomenclatural changes in the Australian and New Zealand Bulbophyllinae and Eriinae (Orchidaceae). Orchadian 13(11): 498-501.
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.
Yukawa, T., Kurita, S., Nishida, M. and Hasebe, M. (1993). Phylogenetic implications of chloroplast DNA restriction site variation in subtribe Dendrobinae (Orchidaceae). Lindleyana 8: 112-221.
Yukawa, T., Ohba, H., Kurita, Cameron, K.M. and Chase, M. W. (1996). Chloroplast DNA phylogeny of subtribe Dendrobinae (Orchidaceae): insights from a combined analysis based on rbcL sequences and restriction site variation. J. Plant Research 109: 169-176.
Yukawa, T. and Uehara, K. (1996), Vegetative diversification and radiation in subtribe Dendrobiinae (Orchidaceae): evidence from chloroplast DNA phylogeny and anatomical characters. Plant Syst. Evol. 201: 1-14.
Yukawa, T., Kita, K. and Handa, T. (2000). DNA phylogeny and morphological diversification of Australian Dendrobium (Orchidaceae). Pp 465-471 in K.L.Wilson and D.A.Morrison (eds), Monocots: Systematics and Evolution (CSIRO Publishing: Melbourne).