Didymoplexis Griff.
Union Burma J.Life Sci. p383, t. 17. (1843)

Name Status: Current
Browse to the list of specimens for Didymoplexis Griff.

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

Family Orchidaceae.

Habit and leaf form. Herbs. Leaves absent. Plants succulent (stem fleshy); saprophytic. Perennial; rhizomatous, or tuberous (with horizontal, tuberous rhizomes). Mesophytic. Stem anatomy. Secondary thickening absent.

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Entomophilous. 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; stem bracts present. Flowers pedicellate (pedicels short at anthesis, elongating in fruit); bracteate (bracts small); small to medium-sized (often ephemeral); 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); joined; without spots, or spotted; white (sometimes tinged with brown or pink in D. pallens). Calyx (if the outer whorl be so designated) 3 (the median member ostensibly posterior); 1 -whorled. Corolla (i.e. the members of the inner whorl) 3, or 6 (by misinterpretation); 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 long, thin, dilated towards the apex, with a short foot); 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, Northern Territory, and Queensland. Northern Botanical Province.

Additional characters Perianth of 5 similar members and the median inner member modified into the labellum (sepals and petals adnate at base to form a tube, the lateral petals adnate to the adaxial sepal for a greater distance than to the lateral sepals; labellum adnate to the tip of the column foot, broad). Column prominently winged. Labellum not insect-like. Perianth not glossy. Labellum with calli.

Taxonomic Literature

  • Wheeler, J. R.; Rye, B. L.; Koch, B. L.; Wilson, A. J. G.; Western Australian Herbarium (1992). Flora of the Kimberley region. Western Australian Herbarium. Como, W.A.