Epiphytes or lithophytes with very short indiscernible rhizomes anchored by thin roots that arise from basal nodes. The erect to porrect cane-like stems grow over 2-3 seasons and are laterally flattened, thin and wiry throughout and with a leaf present at most nodes. The leaves, which are arranged distichously, are longer than wide and basally sheath a node. The short inflorescences emerge from a node opposite a leaf, breaking through its sheath. Each node produces a single inflorescence and after flowering a prominent bract remains protruding at the node. The flowers are borne in pairs, each flower facing inwards towards the other, usually lasting less than a day but in some cases the flowers have been observed to last for two days. It is usual for massed flowering to occur on a plant and for all the plants in an area to flower synchronously. The thin to firm-textured perianth segments are all of similar shape and size. The bases of the lateral sepals are fused with the column foot and the labellum is firmly attached to its apex. The labellum is prominently lobed and the midlobe is variously adorned with hairs and papillae.
Significant Generic Characters
Epiphytic/lithophytic orchids; plants erect to pendulous; stems cane-like, growing over 2-3 seasons, laterally flattened, thin, uniformly thick, wiry; leaves lasting several seasons, distichous, longer than wide, basally sheathing a node; floral nodes producing a single inflorescence; inflorescences short, leaf opposed, breaking through a sheath; after flowering a prominent protruding bract remains; flowers in pairs, each flower facing inwards towards the other, usually lasting less than a day; lateral sepal bases fused with the column foot; labellum firmly attached to the apex of the column foot; labellum lamina 3-lobed; midlobe adorned with hairs and papillae.
Size and Distribution
A genus of about 200 species with its main occurrence in New Guinea, but also distributed in the Sri Lanka, Taiwan, Philippines, Vanuatu, Indonesia, Solomon Islands, New Caledonia, Tahiti and northeastern Queensland where there are 4 species, 3 endemic. The Australian species are distributed between Cape York (10°41' S) and Mt Elliot near Ayr (19°30' S). State occurrence: Queensland.
Species of Grastidium grow on trees and rocks in situations of bright light where the humidity is relatively high and there is ample air movement. 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.
Pollination: The flowers of species of Grastidium usually last less than a day, but on occasions it has been observed that flowers can last 2 days. Most species seem to be insect-pollinated but the vectors are unknown. Some species from New Guinea and some Oceanic islands are known to be autogamous and may even be cleistogamous.
Seasonal Growth: The plants grow actively during the spring and summer months and are relatively quiescent for the remainder of the year.
Flowering: Flowering, which occurs mainly during the warmer months, is initiated by the sudden drenching of plants during heavy rain. This drenching induces a short period of cooling of the plant that triggers floral initiation and flowering takes place 9-10 days later. It is usual for a massed flowering to occur on a plant and all the plants in an area flower synchronously.
Hybrids: Natural hybrids involving species of Grastidium are unknown.
Grastidium refers to the prominent leafy stems of these orchids (Greek, grastis, green fodder or grass).
Perennial, evergreen, epiphytic or lithophytic herbs, sympodial. Plants glabrous. Roots elongate, thin, produced from nodes on the base of the stems. Rhizome superficial, branched. Pseudobulbs absent Stems cane-like, crowded, thin, laterally flattened, capable of growth over 2-3 seasons, erect, porrect or pendulous, when young covered by scarious bracts. Trichomes absent from vegetative parts. Aerial growths produced occasionally from the upper nodes. Leaves lasting several seasons, distichous, sessile, much longer than wide, firm-textured, smooth, not grooved or channelled; base sheathing, the sheath completely enclosing a node; margins entire; apex unequally emarginate. Floral nodes capable of producing a single inflorescence only. Inflorescence short, porrect, arising from a node opposite a leaf and breaking through its sheath, two-flowered, the flowers facing each other. Peduncle very short, with a group of imbricate scarious bracts. Floral bracts scarious, tiny, barely subtending the base of the pedicel. Pedicel relatively long, thin, merging with the ovary. Ovary short, straight, merging with the pedicel. Flowers resupinate, stalked, usually lasting less than a day, but sometimes lasting two days, white, yellow, orange or red. Perianth segments thin to firm-textured, incurved to widely spreading, entire. Dorsal sepal free, subsimilar to the lateral sepals; apex entire or cymbiform. Lateral sepals subsimilar to the dorsal sepal, attached by their bases to the column foot; apex entire or cymbiform. Petals free, subsimilar to the sepals; apex entire. Labellum hinged to the apex of the column foot, markedly dissimilar in size and shape to the sepals and petals, ecalcarate. Labellum lamina variable in shape, thin to fleshy, three-lobed; lateral lobes entire; midlobe short, flared or attenuate, often adorned with trichomes or papillae; margins entire, erose, setulose or fimbriate; apex entire or emarginate. Spur absent. Callus generally superficial, consisting of narrow parallel ridges or plates. Nectar absent. Column lacking free filament and style, fleshy, much shorter than the perianth segments, nearly straight; ventral surface smooth or papillate. Column wings present, reduced, ventral and with short tooth-like apical stelidia. Column foot well developed, as long as or longer than the column, straight or curved. Pseudospur absent. Anther terminal, incumbent, 2-celled, persistent, attached dorsally by a ligulate claw, erostrate; apex smooth. 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; peduncle not elongated in fruit; pedicel not elongated in fruit. Seeds numerous, relatively large, light coloured, winged.
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.