Pholidota imbricata

Rattlesnake Orchids

Erect to creeping epiphytes, lithophytes or terrestrials with prominent pseudobulbs, either clustered or well separated by a rhizome. Pseudobulbs fibrous, with a single node, when young covered by fibrous bracts. Leaves 1-2 per pseudobulb, apical, leathery, longer than wide, flat, stalked. Racemes often arising with the new growth, erect to pendulous, thin, wiry, multiflowered. Flowers alternating in 2 rows, lasting few-several days, white, cream, yellowish or pinkish, relatively small, subtended by large concave bracts that persist after flowering. Dorsal sepal concave. Lateral sepals broadly triangular, asymmetric. Petals smaller than the sepals. Labellum fixed to the column base or the apex of the column foot, deeply saccate at the base, the margins erect to incurved.

Significant Generic Characters

Epiphytic/lithophytic/terrestrial orchids; rhizomes very short or creeping; pseudobulbs fleshy, 1-noded; leaves lasting several seasons, 1-2 per pseudobulb, apical, conduplicate, longer than wide, flat, stalked, articulated on the apex of the pseudobulb; racemes often arising with the new growth, terminal, erect to pendulous, multiflowered; peduncle and rhachis thin, wiry; flowers alternating in 2 rows, lasting few-several days, relatively small, subtended by prominent concave floral bracts which persist for a time after anthesis; perianth segments thin-textured; dorsal sepal concave; lateral sepal triangular, asymmetric; petals smaller than the sepals; labellum fixed to the apex of the column foot or the column base; lamina with a broad deeply saccate basal hypochile and an entire or lobed epichile; column short, with or without a column foot.

Size and Distribution

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A genus of about 29 species widely distributed in China, South-east Asia, Malaysia, Philippines, Indonesia, New Caledonia, New Guinea and Polynesia with 1 non-endemic species, Pholidota imbricata, in Australia. The native species occurs on some Torres Strait Islands and in northeastern Queensland between Cape York (1041 S) and Mt Elliot (2606 S) near Ayr; also known from a single locality in the Northern Territory. State occurrence: Queensland, Northern Territory.

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Ecology

Pholidota imbricata grows on trees, boulders, cliff faces and rocks in open humid sites where there is free air movement. The plants commonly grow in brightly lit humid patches of open forest, on trees overhanging streams, on the upper trunk and branches of rainforest trees and along rainforest margins. The climate is tropical with the majority of rain falling during the summer wet season (December to March) with the remaining months being drier with sporadic or intermittent rain.

Biology

Pollination: The flowers of Pholidota imbricata are insect-pollinated but the vector is unknown.

Reproduction: Reproduction in Pholidota imbricata is solely from seed. Seed dispersal takes 2-4 months after pollination and the capsules develop in a pendant position. In some species the peduncle elongates prior to seed dispersal. Apomixis is unknown in the genus.

Seasonal Growth: Pholidota imbricata plants grow actively during the spring and summer months and are relatively quiescent for the remainder of the year.

Flowering: Flowering occurs mainly between March and May but sporadic flowering can occur at other times.

Hybrids: Natural hybrids involving Pholidota imbricata are unknown.

Derivation

Pholidota is derived from the Greek pholidotos, scaly, in reference to the large bracts which subtend the flowers in some species.

Botanical Description

Perennial, evergreen, epiphytic, lithophytic or terrestrial herbs, sympodial. Plants usually glabrous. Roots elongate, filamentous, branched, produced from nodes on the base of the pseudobulb, adherent or aerial. Rhizome creeping, branched. Pseudobulbs well-developed, single-noded, fibrous, crowded or widely-spaced, short to relatively elongate, when young covered by fibrous bracts. Trichomes sometimes present on floral parts. Aerial growths absent. Leaves lasting several seasons, terminal, 1-2 per shoot, conduplicate, petiolate; lamina longer than wide, coriaceous, smooth, flat; petiole channelled, articulate on the apex of the pseudobulb; margins entire; apex entire or unequally emarginate. Venation parallel, some veins conspicuous. Inflorescence racemose, sometimes synanthous, erect to arcuate or pendulous, terminal, multiflowered. Peduncle equal to or longer than the rhachis, thin, wiry, ebracteate or with scattered scarious bracts.  Floral bracts imbricate when developing, large, alternate, distichous, often foliose, sometimes concave and partly enclosing the flower, persistent. Rhachis straight or flexuose. Pedicel short, thin, straight, curved or twisted, merging with the ovary. Ovary short, straight, non-twisted, porrect from the pedicel, glabrous or pubescent. Flowers resupinate or non-resupinate, alternating in 2 rows, sometimes nearly secund, stalked, lasting few-several days, white, cream, yellowish or pinkish. Perianth segments free, thin-textured, incurved to widely spreading, entire, glabrous or pubescent. Dorsal sepal subsimilar to the lateral sepals, usually concaveLateral sepals asymmetric, usually concave, sometimes carinate. Petals free, smaller than the sepals. Labellum stiffly attached to the column base, markedly dissimilar in size and shape to the sepals and petals, ecalcarate. Labellum lamina developed into a hypochile and epichile; hypochile generally broad and deeply saccate at the base, with erect to spreading margins; epichile well developed or vestigial, often recurved, entire or 2-3-4-lobed. Spur absent. Callus consisting of calli, papillae or median ridges, rarely absent. Nectar present or absent. Column short, at an angle to the end of the ovary, lacking free filament and style, fleshy, shorter than the perianth segments, nearly straight. Column wings obscure, lateral, extending dorsally as a mitra. Column foot absent or small to vestigial. Pseudospur absent. Anther terminal, incumbent, 2-celled, persistent, attached dorsally by a ligulate claw, smooth, erostrate. Pollinarium present, consisting of pollinia attached by elastic caudicles, sometimes with a rostellum. Pollinia 4, orange, soft, mealy, stalked. Viscidium small or absent. Rostellum ventral, small to large, transverse. Stigma entire, transverse, concave. Capsules dehiscent, glabrous or hairy, pendant, with persistent floral remnants; peduncle not or sometimes elongated in fruit; pedicel not elongated in fruit. Seeds numerous, minute, light coloured, winged.

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Taxonomy

Pholidota has been revised (De Vogel 1988).

Nomenclature

Pholidota Lindl. Ex Hook., Exotic Fl. 2, t. 138 (1825). Type species: Pholidota imbricata Hook.

Infrageneric Taxa: Pholidota is a complex genus of 9 sections (De Vogel 1988).

References

De Vogel, E.F. (1988). Revisions in Coelogyninae (Orchidaceae) III. The genus Pholidota. Orch. Monog. 3: 1-116.

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.