Cadetia taylori

Burr Orchids

Epiphytes or lithophytes. Rhizome very short or vestigial, anchored by thin branched roots that arise from basal nodes. Stems well developed, thin to fleshy, crowded, tufted, consisting of several basal nodes and an elongate apical node. Pseudobulbs absent. Leaf solitary, from the apex of a stem, sessile, firm-textured, longer than wide, flat, with an unequally notched apex. Flowers produced in spasmodic bursts, arising singly from a perennial meristem in the leaf axil. Each flower lasts 2-5 days and has relatively thick-textured flat segments. Dorsal sepal smaller than the lateral sepals. Lateral sepal bases partly fused with each other and with the column foot. Petals much narrower than the sepals. Labellum firmly attached to the apex of the column foot and partly to its margins to form a short pseudospur. Labellum lamina distinctly three-lobed; lateral lobes small; mid-lobe thin to broad, shortly hairy. The callus consists of a simple hairy patch.

Similar Genera

Sarcocadetia

Significant Generic Characters

Epiphytic or lithophytic habit; rhizome tufted; pseudobulbs absent; stems thin, consisting of basal nodes and an elongated apical node; stems lasting several seasons; leaf solitary on stem; leaf axil with a single perennial floral meristem; flowers produced 1-3 at sporadic intervals; labellum 3-lobed.

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Size and Distribution

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A genus of about 66 species well developed in New Guinea and the adjacent islands, but also in Indonesia, Philippines, Malaysia, South-east Asia and India. In Australia there are 4 native species, Cadetia clausa, Cadetia maideniana and Cadetia collinsii (in section Cadetia), and Cadetia taylori (section Pterocadetia), the latter 2 species being endemic. All species occur in north-eastern Queensland, mainly between the Iron Range (1236' S) on Cape York Peninsula and the Paluma Range (1910' S) near Townsville, but Cadetia clausa extends northwards into the Torres Strait Islands and possibly into southern New Guinea. State occurence: Queensland (including Moa Island).

Ecology

The native species of Cadetia grow on trees and rocks in rainforest and moist sheltered sites, such as gullies, in open forest. They range from the coastal lowlands to the ranges and tablelands with Cadetia taylori extending to mountain peaks. Cadetia maideniana also grows in mangroves lining coastal estuaries. The prevailing climate where these orchids grow is tropical with the majority of rain falling during the summer wet season (December to March) and the remaining months being much drier.

Biology

Pollination: The flowers of Cadetia clausa, Cadetia maideniana and Cadetia collinsii last for 2-3 days and are self-pollinating, with some variants of Cadetia maideniana self-pollinating without opening. The flowers of Cadetia taylori last longer (up to 5 days) and are insect-pollinated but the vector is unknown.  

Reproduction: Reproduction in Cadetia is mainly from seed, although occasional plants of Cadetia maideniana and Cadetia taylori produce aerial growths. Seed dispersal occurs 6-10 months after pollination and the capsules develop in a nodding 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 spasmodic bursts throughout the year.

Hybrids: Natural hybrids, either interspecific or intergeneric, involving species of Cadetia are unknown.

Derivation

Cadetia is named after Charles Louis Cadet de Gassicourt, 18-19th century French chemist.

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Botanical Description

Perennial, evergreen, epilithic herbs, sympodial. Roots elongate, branched, filamentous, produced from basal nodes. Rhizome short or vestigial. Stems well developed, tufted, crowded, unbranched, thin (section Cadetia) to fleshy (section Pterocadetia), consisting of several basal nodes and an elongate apical node, cylindrical (section Pterocadetia) or dilated distally (section Cadetia). Pseudobulbs absent. Trichomes present on the column and labellum. Aerial growths occasional. Leaves solitary on a stem, sessile, longer than wide, firm-textured, coriaceous, smooth, flat, not grooved or channelled, base not sheathing; margins entire; apex unequally emarginate. Inflorescence single-flowered, arising spasmodically from a perennial meristem situated in the leaf axil; each meristem can produce a number of flowers over time, but usually only a single flower open at any time from each meristem. Peduncle absent.  Floral bracts scarious, persistent, sheathing the base of the pedicel. Pedicel very short, thin, merging with the ovary. Ovary short, straight or curved, porrect from the pedicel, glabrous (section Pterocadetia) or with short, thick, fleshy, bristle-like structures (section Cadetia). Flowers resupinate, stalked, lasting 2-5 days, white or cream with yellow in the labellum. Perianth segments thin-to firm-textured, widely spreading, entire, flat. Dorsal sepal free, narrower than the lateral sepals, straight; apex entire, flat.  Lateral sepals broader than the dorsal sepal, widely spreading, straight, partly fused with each other and attached by their broad bases to the column foot; apex entire. Petals free, of similar length to the sepals but much narrower; 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 firm-textured, three-lobed; lateral lobes relatively small, erect, entire; mid-lobe small (section Cadetia) to well-developed (section Pterocadetia), incurved or recurved, shortly hairy. Callus consisting of a simple hairy patch. Nectar present or absent. Column lacking free filament and style, fleshy, shorter than the perianth segments, nearly straight, anteriorly hairy. Column wings present, well developed, ventral, with several prominent, extended, tooth-like, apical stelidia higher than the anther. Column foot well developed, as long as the column, in line with it, nearly straight. Spur vestigial. Pseudospur present, formed by the union of the anterior basal margins of the lateral sepals, the bases of the lateral sepals with the margins of the column foot and the basal margins of the labellum. Anther terminal, incumbent, 2-celled, persistent, attached dorsally by a ligulate claw, smooth, rostrate; apex smooth. Pollinarium absent. Pollinia 4 in 2 pairs, straight or slightly falcate, yellow or orange, hard, waxy. Viscidium absent. Rostellum ventral, short, broad, sometimes fused with the stigma (section Cadetia). Stigma entire, concave, sometimes fused with the rostellum (section Cadetia). Capsules dehiscent, glabrous (section Pterocadetia), or adorned with soft, fleshy, bristle-like protruberance (section Cadetia), cernuous; peduncle not elongated in fruit; pedicel not elongated in fruit. Seeds numerous, light coloured, winged.

Taxonomy

Within the Dendrobieae, Cadetia is distinguished by its tufted habit, thin stems with an elongated apical node, single terminal leaf and long-lived floral meristem capable of producing 1-3 flowers at sporadic intervals.

Nomenclature

Cadetia Gaud. in Freycinet, Voy. Uranie 422, t.33 (1826). Type species: Cadetia umbellatum Gaud.

Infrageneric Taxa: A genus of 2 sections:

1. Cadetia section Cadetia: Stems thin, terete, round in cross-section; labellum midlobe small; capsules densely covered with soft prickles, round in cross-section.

2. Cadetia section Pterocadetia Schltr. Stems fleshy, angular, ellipsoid to flat in cross-section; labellum midlobe well-developed; capsules smooth, more or less three-winged in cross-section.

References

Schlechter, R. (1982 English translation). The Orchidaceae of German New Guinea, Australian Orchid Foundation.

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