Dendrobium Sw.
Butterfly Orchids

Scientific Description

Family Orchidaceae.

Habit and leaf form. Herbs, or herbaceous climbers. Perennial. Leaves cauline. Plants with neither basal nor terminal concentrations of leaves, or with terminal rosettes of leaves; rhizomatous (most Australian species have a creeping rhizome, terminating in a thickened pseudobulb). Epiphytic (usually), or self supporting (lithophytes), or climbing (then twining). Helophytic, or mesophytic. Leaves medium-sized to large; alternate; spiral, or distichous; leathery (usually, or thin-textured); imbricate, or not imbricate; petiolate; sheathing, or non-sheathing; simple. Leaf blades entire; flat, or solid; if solid, terete; parallel-veined; cross-venulate, or without cross-venules. Leaf blade margins entire. Stem anatomy. Secondary thickening absent. Roots. Roots with velamen (in epiphytic forms), or without velamen.

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Entomophilous (small native bees), or ornithophilous (in D. smilliae), or pollinated by unusual means (self-pollinated). Pollination mechanism conspicuously specialized.

Inflorescence and flower features. Flowers solitary, or aggregated in ‘inflorescences’. Inflorescence few-flowered to many-flowered. Flowers in racemes. The terminal inflorescence unit racemose. Inflorescences scapiflorous, or not scapiflorous; axillary (lateral or subterminal). Flowers bracteate; 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; green, or white, or cream to yellow, or pink, or purple, or red to brown. 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 6 (by misinterpretation); polypetalous; imbricate; (labellum) spurred. Androecium 3, or 1 (by misinterpretation). Androecial members adnate (via fusion of tepals and gynostemium); united with the gynoecium (fused with the style to form a column or ‘gynostemium’; column foot pronounced; apex of column with short teeth, usually one on each side); 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. Anthers dorsifixed to basifixed; dehiscing via longitudinal slits; introrse; tetrasporangiate; usually with a beak-like extension (rostrum). Pollen shed in aggregates; in the form of pollinia (pollinia 2(-4)). 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; 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 septicidal, or loculicidal. 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, 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, or of 5 dissimilar members and the median inner member modified into the labellum (sepals usually curving backwards in the open flower; lateral sepals adnate basally with the column foot to form a chin-like extension (mentum); lateral petals narrower or broader than the sepals; labellum commonly 3-lobed, adnate at least basally to the column foot forming a closed spur; lobes sometimes indistinct, midlobe somewhat fringed, usually with 1–7 longitudinal keels, calli sometimes present). Leaves solitary, or not solitary (the pseudobulb has 1 to few leaves in an apical group, or 1 leaf at each of several nodes). Labellum hinged or fixed. Perianth not glossy.