Dipodium R.Br.
Hyacinth Orchids

Scientific Description

Family Orchidaceae.

Habit and leaf form. Herbs, or herbaceous climbers. Leaves absent (in saprophytic species), or well developed. Plants succulent (stems fleshy), or non-succulent; autotrophic, or saprophytic (D. stenochielum and several eastern Australian species). Perennial; plants with neither basal nor terminal concentrations of leaves; with or without a rhizome. Self supporting (usually), or epiphytic to climbing (D. pandanum). Helophytic, or mesophytic. Leaves medium-sized to very large; alternate; distichous; ‘herbaceous’, or leathery, or fleshy; imbricate, or not imbricate; petiolate; simple. Leaf blades entire; flat; parallel-veined; cross-venulate, or without cross-venules. Leaf blade margins entire. Vernation conduplicate. Stem anatomy. Secondary thickening absent.

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Entomophilous (small bees and wasps). Pollination mechanism conspicuously specialized.

Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in racemes. The terminal inflorescence unit racemose. Inflorescences scapiflorous, or not scapiflorous; terminal, or axillary; erect, apparently terminal on branches of the rhizome in saprophytes, or lateral racemes with few to more than 50 flowers in heterotrophic species. Flowers small to large; fragrant, or odourless; very irregular; zygomorphic; resupinate. The floral asymmetry involving the perianth and involving the androecium. Flowers 3 merous; cyclic; supposedly basically pentacyclic. Perigone tube absent. Perianth of ‘tepals’, or with distinct calyx and corolla, or petaline (by misinterpretation); 6; 2 -whorled, or 1 -whorled (by misinterpretation); isomerous (but zygomorphic); free; petaloid, or sepaloid and petaloid; without spots, or spotted; white, or pink to purple, or red (sometimes with spots), or yellow, or yellow to green (with red spots). Calyx (if the outer whorl be so designated) 3 (the median member ostensibly posterior); 1 -whorled; polysepalous. Corolla (i.e. the members of the inner whorl) 3, or 5–6 (by misinterpretation); polypetalous; imbricate. Androecium 3, or 1 (by misinterpretation). Androecial members free of the perianth, or adnate (? via fusion of labellum and column foot); united with the gynoecium (fused with the style to form a column or ‘gynostemium’; column c. half as long as labellum, moderately stout, dilated towards apex, hairy from the base; apex sometimes irregular); coherent (via the gynostemium); 1 - adelphous; theoretically 2 -whorled. Androecium including staminodes, or exclusively of fertile stamens (by misinterpretation). Staminodes 2 (these anterior (ostensibly posterior), supposedly the abaxial pair of the inner whorl). Stamens 1 (this across the flower from the labellum, i.e. anterior but ostensibly posterior, supposedly representing the outer whorl); reduced in number relative to the adjacent perianth; alterniperianthial (i.e. with reference to the single stamen, across the flower from the labellum); filantherous, or with sessile anthers. Anthers dorsifixed to basifixed; dehiscing via longitudinal slits; introrse; tetrasporangiate; appendaged, or unappendaged. Pollen shed in aggregates; in the form of pollinia (pollinia 2, often deeply grooved, each attached to the retinaculum by a long stipe). Gynoecium 3 carpelled. The pistil 1 celled. Carpels isomerous with the perianth. Gynoecium syncarpous; eu-syncarpous; inferior. Ovary unilocular; 1 locular. The ‘odd’ carpel anterior (away from the labellum). Gynoecium stylate. Styles 1 (inflexed); apical. Stigmas 1 (very high on the column); 3 - lobed (but becoming much modified in form, the apex of the median lobe forming the ‘rostellum’); wet type; papillate; Group III type. Placentation parietal. Ovules not differentiated; in the single cavity 30–100 (i.e. very numerous); non-arillate; anatropous.

Fruit and seed features. Fruit non-fleshy; dehiscent; a capsule. Capsules dehiscing by 6 longitudinal slits. Fruit 30–500 seeded (i.e. seeds usually very numerous). Seeds endospermic (endosperm development arrested very early), or non-endospermic; minute; without starch. Embryo rudimentary at the time of seed release, or weakly differentiated. Seedling. Seedling collar not conspicuous. Primary root ephemeral.

Geography, cytology, number of species. Native of Australia. Not endemic to Australia. Australian states and territories: Western Australia, South Australia, Northern Territory, Queensland, New South Wales, Victoria, and Tasmania. Northern Botanical Province.

Additional characters Perianth of 5 similar members and the median inner member modified into the labellum (the labellum sessile on base of column, distinctly 3-lobed; lateral lobes slender and partly sheathing the column to form a narrow tube; midlobe much larger than lateral lobes, convex, hairy in part). Leaves not solitary. Leaves erect. Column not prominently winged. Labellum not motile. Perianth not glossy.