Terrestrials, usually with 2 swollen fleshy stems, the new stem bearing broad pleated leaves on the upper part, the older stem leafless. Small crowded flowers are borne on slender winged racemes which terminate the new growth. Each flower has relatively narrow sepals and petals and a broad labellum attached by a short claw to the column base. The labellum has 2 short blunt basal lobes which do not extend past the base of the column and a transverse ridge or crest on the labellum base. The labellum apex has 3 distinct apical lobes or teeth. The column is slender without a column foot.
Significant Generic Characters
Terrestrial orchids usually consisting of 2 stems, one leafy the other leafless; roots thin, fleshy, unbranched; stems fleshy, erect, resembling a pseudobulb, relatively long, leafy when growing; leaves few per shoot, distal on the stem, plicate, thin-textured, non-articulate, petiolate or sessile; petiole channelled, basally sheathing the stem; inflorescence racemose, terminal, thin, multiflowered; peduncle winged; flowers non-resupinate, lasting few-several days, small, dull coloured, opening sequentially; sepals and petals free; petals narrower than the sepals; labellum attached to the column base by a short claw, 3-lobed, with 2 very short basal auricles; callus consisting of a transverse ridge or crest on the labellum base; column slender, without a foot; pollinia 4, in 2 pairs, without stalks.
Size and Distribution
A genus of about 8 species in Asia, Taiwan, Malaysia, Philippines, Indonesia, New Guinea and Australia where there is a single non-endemic species, Dienia montana, distributed between Cape York (10°41’S) and Airlie Beach (20º16’S) in northeastern Queensland and in the Northern Territory. State occurrence: Queensland, Northern Territory.
In Australia Dienia montana ranges from the coastal lowlands to about 900 m alt. in the ranges and tablelands of northeastern Queensland. Plants grow in soil and accumulations of litter on boulders in rainforest and sheltered areas of open forest, especially on semi-swampy sites and near streams. The climate has a dominant summer wet season (December to March) when the vast majority of rain falls, with the remaining months being much drier and having sporadic to intermittent rain.
Reproduction: Reproduction in Dienia montana is mainly from seed although occasionally aerial growths are produced from the upper nodes on a stem. Seed dispersal takes 6-10 weeks from pollination and the capsules develop in an erect position. Apomixis is unknown in the genus.
Seasonal Growth: Dienia montana grows actively in spring and summer, sheds its leaves in autumn-winter and is dormant until late spring when a new shoot develops (see also Notes).
Flowering: Dienia montana flowers December to April.
Hybrids: Dienia montana does not participate in natural hybridisation.
The name Dienia, which is derived from the Greek dienos, 2 years old, refers to the fleshy stems each lasting 2 seasons.
Perennial, deciduous, terrestrial herbs, sympodial. Plants glabrous, usually consisting of 2 stems. Roots filamentous, thin, fleshy, unbranched, produced from the base of a shoot. Stems appearing pseudobulbous, fleshy, short to elongate, usually erect. Pseudobulbs absent. Trichomes absent. Leaves plicate, convolute, lasting 1 season, mainly towards the stem apex, non-articulate, often asymmetric, petiolate or sessile; petiole channelled, its base sheathing the stem. Venation parallel. Inflorescence racemose, many-flowered, erect, terminal. Peduncle shorter or equal to the rhachis, alate, ribbed or grooved, with scattered narrow sterile bracts. Rhachis shorter or equal to the peduncle, straight, alate, ribbed or grooved. Floral bracts narrow, partly sheathing. Pedicels short to vestigial, thin, merging with the ovary. Ovary short, straight, smooth. Flowers non-resupinate, small, crowded, dull coloured (green, yellow, red or purple), shortly pedicellate. Perianth segments free, spreading or incurved. Dorsal sepal narrower than the lateral sepals. Lateral sepals broader than the dorsal sepal. Petals narrower than the sepals, falcate, entire. Labellum fixed by a basal claw to the anterior column base, markedly dissimilar in size to the sepals and petals, ecalcarate. Labellum lamina obscurely 3-lobed or unlobed, shallowly concave, with 2 very short basal auricles flanking the column (auricles sometimes vestigial); apical margins tridentate or trilobed. Spur absent. Callus consisting of a transverse ridge or crest on the labellum base, often thickened in the centre. Nectar absent. Column slender, lacking free filament and style. Column foot absent. Pseudospur absent. Column wings short, erect. Anther terminal, incumbent, shallowly concave, 2-celled, persistent, basifixed, smooth, erostrate. Pollinarium absent. Pollinia 4 in 2 pairs, clavate, yellow, hard, waxy, without caudicles. Viscidium absent. Rostellum blunt, transverse. Stigma entire, concave. Capsules dehiscent, glabrous, erect; peduncle not elongated in fruit; pedicels not elongated in fruit. Seeds numerous, light coloured, winged.
Dienia has been included with Malaxis by many authors but can be distinguished by its above-ground stems, broad pleated leaves and lobed labellum with a trilobate or tridentate apex. Dienia can be distinguished from Crepidium by its clawed labellum with greatly reduced basal auricles and transverse ridge or crest on the labellum base that is often thickened centrally.
Plants of Dienia montana have a stem that grows for a season, loses its leaves and is dormant for a short period during the dry winter season, after which a new shoot arises from a basal node to produce the next seasons growth. The old stem decays as the new stem matures and flowers.
Cameron, K.M. (2005). Leave it to the leaves: a molecular phylogenetic study of Malaxideae (Epidendroideae, Orchidaceae). Am. J. Bot. 92: 1025-1032.
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.
Szlachetko, D.L. (1995). Systema Orchidalium. Fragm. Flor. Geobot. Suppl. 3: 1-152.