Terrestrials, either leafless or with leafy shoots, rarely leafy epiphytes with spirally climbing stems. Leaves, if present, long, narrow, stalkless, channelled and arranged in 2 ranks. Inflorescences are usually long, unbranched and with moderately large colourful flowers. The labellum, which is fixed to the base of the column, sits in close proximity to the column, has narrow lateral lobes, a projecting midlobe with a prominent patch of erect hairs and 2 shortly hairy ridges. The column is long and narrow, with a patch of short hairs near the base.
Significant Generic Characters
Mycotrophic or autotrophic terrestrials, rarely autotrophic epiphytes with spirally climbing stems; stems emergent or subterranean, fibrous, multinoded; leaves, when present, distichous, sessile, much longer than wide, channelled; inflorescence lateral, racemose; flowers moderately large, lasting many days, colourful, often spotted or blotched; sepals and petals subsimilar; labellum fixed to the column base; lamina 3-lobed, without a spur; lateral lobes, narrow, column-embracing; midlobe porrect, with a prominent patch of erect hairs; callus of 2 pubescent ridges; column elongate, fleshy, with an anterior pubescent patch, without a foot; pollinia 2, each on stipe, sometimes the stipes joined at the base.
Size and Distribution
A genus of about 30 species distributed in Malaysia, Philippines, Indonesia, Solomon Islands, New Hebrides, New Caledonia, New Guinea and Australia where there are 11 endemic species. Of the Australian species, 9 grow as leafless hemiparasites and 2 are leafy autotrophic species, one growing as a terrestrial and the other as a climbing epiphyte. The native leafless species are distributed in temperate and tropical regions whereas the leafy species are restricted to the tropics. State occurrence: Queensland, New South Wales, Australian Capital Territory, Victoria, Tasmania, South Australia, Western Australia, Northern Territory.
The leafless terrestrial species mainly grow in forested habitats dominated by eucalypts and bloodwoods, always in well-drained soil. Dipodium ensifolium grows in similar habitats and extends to rainforest margins. The climbing epiphytic species, Dipodium pandanum, is restricted to rainforest.
Reproduction: Reproduction in Dipodium is mainly from seed. Seed dispersal takes 3-6 months from pollination and the capsules develop in a pendant position. Dipodium pandanum is a climbing species that has a secondary method of reproduction whereby the plants break up as the stems elongate and the fragmented sections fall to the ground and develop as separate plants. By this means the species forms localised clumps with the majority of plants probably of clonal origin.
Seasonal Growth: Plants of Dipodium ensifolium and Dipodium pandanum are evergreen and grow mainly during the wet season (summer-autumn).
Flowering: Most native species of Dipodium flower in spring and summer; Dipodium pandanum flowers sporadically in winter, spring and early summer.
Hybrids: Natural hybrids involving the native species of Dipodium are unknown.
Fire: The leafless species of Dipodium and Dipodium ensifolium grow in fire-prone habitats. The leafless species are unaffected by fire, however the above-ground parts of Dipodium ensifolium are destroyed by fire but the plants quickly reshoot. There is no evidence of fire stimulation in any species. Dipodium pandanum grows in habitats that are not fire-prone.
The name Dipodium is derived from the Greek di, double and podion, little foot, in reference to the 2 stipes in the pollinaria.
Perennial, leafless or leafy, geophytic or climbing herbs, hemiparasitic or autotrophic, leafless or evergreen, monopodial. Plants glabrous. Roots thick and fleshy. Stems short to long, consisting of few to many nodes, fibrous to woody, emergent or subterranean. Trichomes present on the labellum. Leaves present or absent (reduced to fleshy bracts), if present many per shoot, spreading, distichous, much longer than wide, lasting several seasons, conduplicate, smooth, sessile; bases closely imbricate, persistent. Venation unknown. Flowering and non-flowering plants monomorphic. Inflorescence racemose, axillary, multiflowered. Peduncle subsimilar to or longer than the rhachis, with few-several tubular or semi-tubular sterile bracts. Rhachis straight, shorter than or similar to the peduncle. Floral bracts narrow, scarious, partially sheathing the base of the pedicel. Pedicel short to moderately long, thin, merging with the ovary. Ovary short, straight, curved or gibbous. Flowers resupinate, moderately large, lasting several days, opening sequentially, white, pink, mauve, purple or yellow, often spotted or blotched, pedicellate, scentless. Perianth segments fleshy, porrect to spreading. Dorsal sepal free, similar, or subsimilar to the lateral sepals. Lateral sepals free, similar or subsimilar to the dorsal sepal. Petals subsimilar to or smaller than the sepals. Labellum fixed to the column base, parallel with the column, the basal part closely embracing the column, markedly dissimilar in size and shape to the sepals and petals, ecalcarate. Labellum lamina 3-lobed; lateral lobes, narrow, entire, obliquely erect and column-embracing; midlobe porrect, elongate, with a prominent medial patch of erect hairs; margins flat or revolute; apex narrowed, often decurved. Spur absent. Callus consisting of 2 parallel or divergent pubescent ridges. Nectar absent. Column porrect from the end of the ovary, narrow, elongate, straight, lacking free filament and style, fleshy, pubescent on a proximal ventral area. Column wings greatly reduced to vestigial, terminal. Column foot absent. Pseudospur present as a short tunnel formed by the labellum base and flanked by the lateral lobes and ventral surface of the column. Anther terminal, incumbent, 2-celled, persistent, smooth, with a broad porrect rostrum. Pollinarium present. Pollinia 2, notched or deeply cleft, hard, waxy, stalked, either basally attached to a common stipe or each pollinium with its own stipe attached directly to a viscidium. Stipe short and broad or elongate. Viscidium relatively large. Rostellum small, entire. Stigma entire, large, terminal, concave. Capsules dehiscent, glabrous, pendant; peduncle not elongated in fruit; pedicel not elongated in fruit. Seeds numerous, light coloured, winged.
As currently interpreted Dipodium exhibits limited floral divergence, apart from interesting variation in the morphology of the pollinarium, but shows significant vegetative polymorphy within the genus. This latter aspect suggests a detailed molecular study is needed to elucidate relationships within the genus.
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