Ceratobium dalbertisii

Antelope Orchids

Epiphytes or lithophytes with very short indiscernible rhizomes anchored by roots that arise from nodes at the base of the pseudobulb. Pseudobulbs hard, cane-like, elongated, usually thickened in the proximal half, attenuated towards the apex, often with swollen nodes and narrower internodes. Leaves on the upper half of the pseudobulbs, thick and fleshy, longer than wide, flat or shallowly concave, without any channel or groove, basally sheathing; apex unequally notched. Inflorescence racemose, from the upper nodes of a pseudobulb. Flowers long-lasting, relatively large, thick-textured.  Perianth segments often irregularly wavy or twisted. Sepals subsimilar. Lateral sepal bases fused with the column foot. Petals longer than the sepals. Labellum stiffly attached to the apex of the column foot. Labellum lamina distinctly three-lobed, relatively thick and fleshy, with prominent central ridges and a short basal spur.

Significant Generic Characters

Epiphytic/lithophytic orchids; rhizomes very short, indiscernible; pseudobulbs hard, cane-like, elongated, usually thickened in the proximal half, attenuated towards the apex, often with swollen nodes and narrower internodes; leaves lasting several seasons, occurring on the distal nodes, thick, fleshy, longer than wide, flat or shallowly concave, basally sheathing; inflorescence racemose, from the upper nodes of a pseudobulb; flowers long-lasting, relatively large, thick-textured; perianth segments often irregularly wavy or twisted; sepals subsimilar; lateral sepal bases fused with the column foot; petals longer than the sepals; labellum stiffly attached to the apex of the column foot; lamina distinctly three-lobed, relatively thick, fleshy, with a short basal spur; callus with prominent ridges.

Size and Distribution

click to view 
distribution map

A genus of about 8 species distributed in the southern Philippines, Moluccas, Indonesia, Solomon Islands, New Guinea and northeastern Queensland where there is a single non-endemic species. The Australian species, Ceratobium dalbertisii, is restricted to the coastal side of the McIlwraith range on Cape York Peninsula (c. 1346' S), but is common in New Guinea. State occurrence: Queensland.

^ top

Ecology

Ceratobium dalbertisii occurs on the upper branches of trees (often wattles) in lowland rainforest and on trees beside streams, always in situations of bright light. 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 Ceratobium dalbertisii are very long lasting and are pollinated by large wasps and hornets.

Reproduction: Reproduction in Ceratobium dalbertisii is solely from seed. Seed dispersal takes 4-6 months after pollination and the capsules develop in a pendulous position with the flower parts becoming fleshy and persisting. 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 from autumn to spring.

Hybrids: Natural hybrids involving Ceratobium dalbertisii in Australia are extremely rare.

Derivation

Ceratobium, which is derived from the Greek ceratos, horn and bios, life, refers to the horny life these orchids have (actually it refers to the prominent, erect, horn-like petals).

Botanical Description

Perennial, evergreen, epilithic herbs, sympodial. Roots elongate, produced from nodes on the base of the pseudobulb. Rhizome superficial, branched. Pseudobulbs well-developed, crowded, hard, elongate, thickened towards the base, attenuate towards the apex, the nodes swollen, internodes narrow, when young covered by scarious bracts. Trichomes absent. Aerial growths often present, arising from the apical nodes on the pseudobulbs. Leaves lasting several seasons, distichous, occurring on distal nodes, sessile, much longer than wide, thick and fleshy, coriaceous, smooth, not grooved or channelled; base sheathing the pseudobulb; margins entire; apex unequally emarginate. Inflorescence racemose, erect to arcuate, arising from an apical node on a mature pseudobulb, multiflowered. Peduncle shorter or longer than the rhachis, the base covered with imbricate scarious bracts.  Floral bracts scarious, sheathing the base of the pedicel. Pedicel short to long, thin, merging with the ovary. Ovary short, straight, sometimes at right angles to the pedicel. Flowers resupinate, stalked, lasting many days, green, brown (non-Australian) or white; labellum with distinct striae. Perianth segments thick-textured, widely spreading, entire, the petals straight or twisted. 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, often erect, longer than the sepals; apex entire. Labellum stiffly attached to the apex of the column foot (see also spur below), markedly dissimilar in size and shape to the sepals and petals, calcarate. Labellum lamina more or less oblong, fleshy, strongly three-lobed; lateral lobes large, erect, flanking the column or incurved, entire; mid-lobe short, porrect to recurved; apex entire or apiculate. Spur absent. Callus consisting of narrow parallel ridges, sometimes irregular on the mid-lobe. Nectar absent. Column lacking free filament and style, fleshy, 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 or longer than the column, straight or curved. Pseudospur present, formed by the fused elongated base of the labellum and apex of the column foot. Anther terminal, incumbent, 2-celled, persistent, attached dorsally by a ligulate claw, smooth, erostrate; apex papillate. 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; perianth parts remaining turgid with the development of the capsule; peduncle not elongated in fruit; pedicel not elongated in fruit. Seeds numerous, relatively large, light coloured, winged.

^ top

Taxonomy

Ceratobium, originally described as a section within Dendrobium, was recently raised to generic rank (Clements and Jones 2002).

Nomenclature

Ceratobium M.A.Clem. and D.L.Jones, Orchadian 13(11): 486 (2002); Dendrobium section Ceratobium Lindl., in Edwards's Bot. Reg. 30: misc. 62 (1844).

Type species: Dendrobium antennatum Lindl. [Ceratobium antennatum (Lindl.) M.A.Clem. and D.L.Jones].

Infrageneric Taxa: No infrageneric taxa are currently recognised.

References

Clements, M.A. and Jones, D.L. (2002). Nomenclatural changes in the Dendrobieae (Orchidaceae). 1: The Australasian Region. Orchadian 13(11): 485-492.

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.