Erect to straggly epiphytes with thick flattish roots and long fibrous leafy stems branching from near the base. The narrow, thick, moderately-spaced leathery leaves are arranged in 2 ranks or in a loose spiral. Inflorescences are very short racemes, the main stalk usually thickened and club -shaped. The flowers, which last a few days, are produced at sporadic intervals. Each is carried on a strongly curved stalk. The flowers have petals longer than the sepals and a large fleshy labellum fixed to the base of the column. The column is short and lacks a column foot.
Significant Generic Characters
Straggly epiphytic orchids; plants large, erect or drooping; roots thick, flattish; stems long, fibrous, branched from the base; leaves terete, moderately-spaced, arranged in 2 ranks or a loose spiral, much longer than wide, thick, leathery; inflorescence an abbreviated raceme with a thickened rhachis; flowers opening sporadically; sepals dissimilar; petals longer and narrower than the sepals; labellum firmly attached to the base of the column; lamina divided into a hypochile and epichile; hypochile narrower than the epichile, usually concave or channelled; epichile broad, fleshy, often with a median plate or groove; column short, lacking a foot; pollinia 2, sessile or stalked on a stipe.
Size and Distribution
A genus of about 30 species distributed in Asia, Japan, India, Malaysia, Polynesia, Philippines, Indonesia, New Guinea and Australia where there are 2 endemic species . One native species is restricted to northern parts of the Northern Territory and the other occurs in some Torres Strait islands and on the mainland is distributed between Cape York and the Daintree River in northeastern Queensland. State occurrence: Queensland (including Moa and Dauan Islands), Northern Territory.
Ecology
The native species of Luisia grow on papery- or rough-barked trees in rainforest at low altitudes, usually in bright light and high humidity. 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 Luisia are produced a few at a time in sporadic intervals, the scape lengthening slightly between each batch of flowers. Each flower lasts several days. They are probably pollinated by native bees.
Reproduction: Reproduction in Luisia is solely from seed. Seed dispersal takes 10-12 months after pollination and the capsules develop in an erect position. Apomixis is unknown in the genus.
Seasonal Growth: Luisia plants grow mainly during the spring and summer months and are relatively quiescent for the remainder of the year.
Flowering: The native species of Luisia flower sporadically between spring and autumn.
Hybrids: Natural hybrids involving the native species of Luisia are unknown.
Derivation
Luisia is named after Don Luis de Torres, a 19th century Spanish botanist.
Botanical Description
Perennial, evergreen, straggly epiphytic herbs, monopodial. Roots thick, flattish, elongate, much branched, mainly adherent. Plants small to large, branched from the base, erect or drooping. Stem relatively thick, short to long, fibrous, leafy towards the apex. Pseudobulbs absent. Trichomes usually present on the labellum. Leaves lasting several seasons, terete, distichous, sessile, moderately-spaced, spreading widely, much longer than wide, thick, coriaceous; base sheathing the stem, imbricate with its neighbour, persistent after leaf abscission; margins entire; apex entire. Inflorescence lateral, an abbreviated raceme, lengthening slowly and producing 1-few flowers at sporadic intervals. Peduncle similar or shorter than the rhachis, with semi-tubular, truncate, imbricate bracts. Rhachis straight, thick, clavate. Floral bracts small, non-persistent, scarious, partly sheathing the base of the pedicel. Pedicel short, merging with the ovary. Ovary short, strongly curved. Flowers resupinate, produced 1-few at sporadic intervals, stalked, lasting a few days, greenish with a red labellum. Perianth segments relatively thin-textured (except for the epichile), usually incurved. Dorsal sepal free, narrower than the lateral sepals. Lateral sepals free, broader than the dorsal sepal, usually flanking the labellum. Petals free, longer and narrower than the sepals. Labellum stiffly attached to the base of the column, markedly dissimilar in size and shape to the sepals and petals, ecalcarate. Labellum lamina divided into a hypochile and epichile; hypochile narrower than the epichile, concave or channelled, sometimes with small lateral lobes; epichile broad, fleshy, entire. Spur absent. Callus consisting of a median plate or groove, sometimes obscure. Nectar unknown. Column short, porrect from the apex of the ovary, lacking free filament and style, fleshy, straight. Column wings absent or vestigial. Column foot absent (? Rarely vestigial). Pseudospur absent. Anther terminal, incumbent, 2-celled, persistent, smooth, with a short decurved rostrum. Pollinarium present. Pollinia 2, orange, hard, waxy, sessile or stalked. Stipe short, relatively broad. Viscidium small. Rostellum short, broad. Stigma entire, concave. Capsules dehiscent, elongate, glabrous, erect; peduncle not elongated in fruit; pedicel not elongated in fruit. Seeds numerous, light coloured, winged.
Taxonomy
Within the Vandeae, Luisia is distinguished by straggly habit, long fibrous basally branched stems, thick, terete leathery leaves, abbreviated racemose inflorescence with a thickened rhachis, sharply curved flower stalks, petals longer and narrower than the sepals, labellum firmly attached to the column base, the lamina with a narrow basal hypochile and broad epichile, column short, without a foot and, 2 sessile or stalked pollinia.
Notes
Luisiaplants form coarse straggly clumps that branch from near the base. Young plants are generally erect but in large plants the stems tend to droop.
Nomenclature
Luisia Gaud. in Freycinet, Voy. Uranie 426, t.37 (1826). Type species: Luisia teretifolia Gaud.
Infrageneric Taxa: No infrageneric taxa are currently recognised.
References
Dockrill, A.W. (1967). Australasian Sarcanthinae. The Australasian Native Orchid Society, Sydney.
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.
Seidenfaden, G. (1971). Notes on the genus Luisia. Dansk Bot. Ark. 27(4): 55-61.