Diuris Sm.
Trans.Linn.Soc.London,Bot. 4:222 (1798)

Name Status: Current
Browse to the list of specimens for Diuris Sm.

Scientific Description
H.R. Coleman, Thursday 8 September 2016

Family Orchidaceae.

Habit and leaf form. Herbs. Perennial. Leaves basal. Tuberous. Helophytic, or mesophytic. Leaves medium-sized to very large; alternate, or whorled (forming a tussock when several); when alternate, distichous; ‘herbaceous’; imbricate, or not imbricate; petiolate; simple. Leaf blades entire; flat; linear; parallel-veined; cross-venulate, or without cross-venules. Leaf blade margins entire. Vernation conduplicate. Leaf anatomy. Hairs absent. Stem anatomy. Secondary thickening absent.

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Floral nectaries absent. Entomophilous (small native bees). Pollination mechanism conspicuously specialized (the central parts of the flower mimic co-blooming peas such as Daviesia, Pultinaea and Isotropis and it has been noticed that bees, while visiting the pea flowers for nectar, occasionally explore Diuris flowers in the same way and, in the process, either remove or deposit pollen).

Inflorescence and flower features. Flowers solitary, or aggregated in ‘inflorescences’. Inflorescence several-flowered. Flowers when aggregated, in racemes (loose). The terminal inflorescence unit racemose. Inflorescences scapiflorous, or not scapiflorous; terminal; stem bracts usually 1–4, erect, sheathing. 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; 6; 2 -whorled; isomerous (but zygomorphic); free; sepaloid and petaloid; without spots, or spotted; yellow, or yellow and brown, or yellow and purple, or yellow and orange, or pink and white, or purple. 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; polypetalous; imbricate. Petals clawed (lateral petals). Androecium 3, or 1 (by misinterpretation). Androecial members free of the perianth; united with the gynoecium (fused with the style to form a column or ‘gynostemium’; column very short); 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 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, South Australia, Queensland, New South Wales, Victoria, Australian Capital Territory, and Tasmania. South-West Botanical Province.

Additional characters Perianth of 5 dissimilar members and the median inner member modified into the labellum (adaxial sepal rather broad, its base clasping the column; lateral sepals usually pendulous, parallel or crossed, usually narrowly linear, longer than the adaxial sepal; lateral petals erect or spreading, longer the adaxial sepal, clawed, with a broad, somewhat rounded, lamina; labellum usually intermediate in length between the lateral sepals and petals, deeply 3-lobed, the middle lobe broad). Leaves solitary, or not solitary (2–10 or more). Leaves erect (spirally twisting in some species). Labellum not insect-like. Perianth not glossy.

Taxonomic Literature

  • Wheeler, Judy; Marchant, Neville; Lewington, Margaret; Graham, Lorraine (2002). Flora of the south west, Bunbury, Augusta, Denmark. Volume 1, introduction, keys, ferns to monocotyledons. Australian Biological Resources Study. Canberra.
  • Brown, Andrew; Hoffman, Noel (1995). Orchids of south-west Australia. University of W.A. Press. Nedlands, W.A.
  • (1989-). Australian orchid research. Australian Orchid Foundation. Essendon, Vic.