Cepobaculum canaliculatum

Tea-tree Orchids

Epiphytes or lithophytes with very short indiscernible rhizomes anchored by roots that arise from nodes at the base of the pseudobulb. Pseudobulbs range from short and onion-like to elongate, hard, cane-like and more or less cylindrical. Leaves more or less confined to the apical region of the pseudobulbs, thick and fleshy, longer than wide, ranging from linear-terete with a dorsal channel to flat, without any channel or groove, basally sheathing and with an entire or unequally notched apex. Inflorescence racemose, long, arising from the upper nodes of a pseudobulb. Flowers long-lasting, relatively large, thick-textured, sometimes scented.  Perianth segments often irregularly wavy or twisted. Sepals subsimilar. Bases of the lateral sepals 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.

Similar Genera

Durabaculum

Significant Generic Characters

Epiphytic/lithophytic orchids; rhizomes indiscernible; pseudobulbs short and onion-like to elongate and cane-like; leaves lasting several seasons, restricted to distal nodes, thick, fleshy, longer than wide, ranging from linear-terete with a dorsal channel to flat, basally sheathing; inflorescence racemose, from the upper nodes of a pseudobulb; flowers long-lasting, relatively large, thick-textured, sometimes scented; perianth segments often irregularly wavy or twisted; sepals subsimilar; bases of the lateral sepals fused with the column foot; petals longer than the sepals; labellum stiffly attached to the apex of the column foot; lamina three-lobed, relatively thick, fleshy; callus with prominent ridges.

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Size and Distribution

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distribution map

A genus of about 8 species distributed in Indonesia, New Guinea and northeastern Queensland where there are 6 species, 2 endemic. The Australian species are variously scattered between the Torres Strait islands (925' S on Dauan Island) and near Rockhampton (2322' S). Two species also occur on Melville Island, one extending to northern mainland parts of the Northern Territory and the Kimberley region of Western Australia. State occurrence: Queensland (including Moa, Saibai and Thursday Islands), Northern Territory, Western Australia.

Ecology

The Australian species of Cepobaculum are frequent in lowland and coastal areas and a couple of species extend into the ranges and tablelands at low to moderate altitudes. They occur on trees and rocks in brightly lit, moist or humid but airy habitats, including rainforest, open forest, woodland, swamp forest, coastal scrubs and mangroves. 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.

Biology

Pollination: The flowers of species of Cepobaculum last many days and are pollinated by large wasps and hornets.

Reproduction: Reproduction in Cepobaculum 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 from autumn to spring.

Hybrids: Natural hybrids involving species of Cepobaculum are rare (example Cepobaculum canaliculatum x Cepobaculum johannis). Sporadic intergeneric hybrids are also known (examples Cepobaculum johannis x Durabaculum undulatum; Cepobaculum canaliculatum x Durabaculum undulatum; Cepobaculum foelschei x Vappodes dicupha).

Derivation

Cepobaculum, which is derived from the Latin cepo, onion and baculus, cane, refers to the onion-like pseudobulbs found in some species.

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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, either short and onion-like or elongate, nearly cylindrical, 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, restricted to distal nodes, sessile, much longer than wide, thick and fleshy, coriaceous, smooth, either linear-terete with a ventral channel or flat, not grooved or channelled; base sheathing the pseudobulb; margins entire; apex entire or 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, thin, merging with the ovary. Ovary short, straight, sometimes at right angles to the pedicel. Flowers resupinate, stalked, lasting many days, brown, white or yellow; labellum with distinct striae. Perianth segments thick-textured, widely spreading, entire or with undulate margins, 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, longer than the sepals; apex entire. Labellum stiffly attached to the apex of the column foot, 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, often becoming enlarged and 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 as 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 or with a short rostrum; 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, vertical, concave. Capsules dehiscent, glabrous, pendulous; peduncle not elongated in fruit; pedicel not elongated in fruit. Seeds numerous, light coloured, winged.

Taxonomy

Cepobaculum is a recent segregate from Dendrobium (Clements and Jones 2002). All species were previously included in the poorly defined Dendrobium section Spatulata Lindl., which included at least 3 groups that are now treated as distinct genera.

Nomenclature

Cepobaculum M.A.Clem. and D.L.Jones, Orchadian 13(11): 486 (2002).

Type species: Dendrobium canaliculatum R.Br. [Cepobaculum canaliculatum (R.Br.) 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.

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