Xyris L.

Scientific Description

Family Xyridaceae.

Habit and leaf form. Herbs. Perennial; plants with a basal concentration of leaves; rhizomatous. Helophytic, or mesophytic, or xerophytic. Leaves alternate; distichous; ‘herbaceous’, or leathery; sessile; sheathing. Leaf sheaths with free margins. Leaves edgewise to the stem, or with ‘normal’ orientation; simple. Leaf blades entire; flat, or solid; linear; linear to oblong; parallel-veined; without cross-venules. Leaves ligulate, or eligulate. Vegetative anatomy. Plants without silica bodies. Stem anatomy. Secondary thickening absent.

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Floral nectaries absent (nectaries lacking). Entomophilous.

Inflorescence and flower features. Flowers aggregated in ‘inflorescences’. Inflorescence few-flowered to many-flowered (2–30-flowered). Flowers in spikes. Inflorescences simple. The terminal inflorescence unit racemose. Inflorescences scapiflorous (scape terete to flattened, straight or twisted); spike ovoid, obovoid or subglobose, compact, with spiral imbricate bracts surrounding solitary flowers, the basal bracts sterile. Flowers bracteate; ebracteolate; small, or medium-sized; somewhat irregular to very irregular; when irregular, zygomorphic. The floral asymmetry involving the perianth, or involving the perianth and involving the androecium (when the androecium distally displaced to one side of the flower). Flowers 3 merous; cyclic; tetracyclic, or pentacyclic. Perigone tube absent. Hypogynous disk absent. Perianth with distinct calyx and corolla (ostensibly), or of ‘tepals’; 6; 2 -whorled; isomerous; free; having the outer and inner members sepaloid and petaloid (respectively); different in the two whorls. Calyx if the outer perianth be so interpreted, 3; 1 -whorled; polysepalous; unequal but not bilabiate (lateral sepals with or without well-developed keel; dorsal sepal thin, membranous, covering the flower in bud, falling off at anthesis); persistent. Corolla if the inner perianth be so interpreted, 3; 1 -whorled; polypetalous; imbricate; regular; yellow (usually), or white. Petals clawed. Androecium 3, or 6. Androecial members adnate (to petal claw); free of one another; 1 -whorled, or 2 -whorled. Androecium exclusively of fertile stamens (the inner whorl), or including staminodes. Staminodes when present, 3 (the outer whorl); non-petaloid (generally bifurcate, often tail-like and plumose). Stamens 3; isomerous with the perianth; oppositiperianthial. Filaments linear or trapezoid. Anthers dehiscing via longitudinal slits; latrorse; tetrasporangiate. Pollen shed as single grains. Gynoecium 3 carpelled. The pistil 1 celled, or 3 celled. Carpels isomerous with the perianth. Gynoecium syncarpous; synstylovarious to eu-syncarpous; superior. Ovary unilocular, or plurilocular; 1 locular, or 3 locular (or incompletely trilocular). Gynoecium stylate. Styles 1; undivided or three-branched; apical. Stigmas 1, or 3; horseshoe-shaped. Placentation when unilocular, parietal, or basal; when trilocular, axile. Ovules in the single cavity when unilocular, 1–100 (to ‘many’ ?); 1–50 per locule (to ‘many’ ?); non-arillate; orthotropous, or anatropous to campylotropous.

Fruit and seed features. Fruit non-fleshy; dehiscent; a capsule. Capsules loculicidal, or circumscissile (rarely). Seeds oblong to ellipsoid; endospermic. Endosperm oily, or not oily. Seeds wingless. Embryo rudimentary at the time of seed release to weakly differentiated (small to large). Seedling. Hypocotyl internode present. Mesocotyl absent. Seedling collar not conspicuous. Cotyledon hyperphyll elongated; assimilatory; dorsiventrally flattened. Coleoptile absent. Seedling cataphylls present. First leaf ensiform. Primary root ephemeral.

Physiology, biochemistry. Aluminium accumulation demonstrated.

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. X = 9, 13, 17.

Economic uses, etc. Supplies watergarden and aquarium ornamentals.