Rostellularia Rchb.

Scientific Description

Family Acanthaceae.

Habit and leaf form. Herbs (with cystoliths). The herbs annual to perennial. Young stems usually 6-angled. Hydrophytic, or helophytic, or mesophytic, or xerophytic. Leaves opposite (decussate); petiolate, or sessile; gland-dotted, or not gland-dotted; simple. Leaf blades entire; flat; pinnately veined, or palmately veined; cross-venulate. Leaves without stipules. Leaf blade margins entire. Stem anatomy. Nodes unilacunar. Secondary thickening developing from a conventional cambial ring. Roots. Aerial roots present, or absent.

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Entomophilous. Pollination mechanism conspicuously specialized, or unspecialized.

Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in spikes (of overlapping bracts, dense). The terminal inflorescence unit cymose, or racemose. Inflorescences terminal. Flowers uni- bracteate; bi- bracteolate; very irregular; zygomorphic. The floral asymmetry involving the perianth. Flowers 4 merous, or 5 merous; tetracyclic. Free hypanthium absent. Hypogynous disk present; annular (with 2 small appendages on either side). Perianth with distinct calyx and corolla; 8–10; 2 -whorled; isomerous, or anisomerous. Calyx 4, or 5 (when remnant of 5th lobe present); 1 -whorled; gamosepalous; lobed; regular (the 4 lobes equal), or unequal but not bilabiate (when 5th lobe present); when K5, with the median member posterior. Corolla 4, or 5; 1 -whorled; gamopetalous; imbricate, or contorted, or with open aestivation; not twisted through 180 degrees; bilabiate. Androecium 2. Androecial members adnate; all equal; free of one another; 1 -whorled. Stamens 2; all inserted at the same level; exserted from throat, covered by upper lip; reduced in number relative to the adjacent perianth; oppositisepalous; all alternating with the corolla members. Anthers dorsifixed; dehiscing via longitudinal slits; bilocular; tetrasporangiate; appendaged. The anther appendages basal (white, on the lower cell). Pollen shed as single grains. Gynoecium 2 carpelled. The pistil 2 celled. Gynoecium syncarpous; synstylovarious to eu-syncarpous; superior. Ovary plurilocular; 2 locular. Gynoecium median. Ovary sessile. Styles 1; attenuate from the ovary; apical; much longer than the ovary at anthesis. Stigmas 1; obscurely notched; dry type; non-papillate; Group II type. Placentation axile. Ovules 2 per locule; superposed; non-arillate, or arillate; hemianatropous, or anatropous, or campylotropous.

Fruit and seed features. Fruit non-fleshy; dehiscent; a capsule (ellipsoid, base solid). Capsules loculicidal. Fruit elastically dehiscent. Dispersal unit the seed. Fruit 4 seeded. Seeds compressed, more or less circular; non-endospermic; not conspicuously hairy. Embryo well differentiated. Cotyledons 2. Embryo achlorophyllous; curved; large. Testa with tubercles. Seedling. Germination phanerocotylar.

Physiology, biochemistry. Aluminium accumulation not found.

Special features. The seeds on elongated, indurated, hook-shaped funicles (‘retinacula’). The upper (posterior, adaxial) lip of the corolla entire, or bilobed (then notched); upper (adaxial) lip of the corolla porrect, with a style channel. Lower (abaxial) lip of the corolla spreading, the middle lobe outermost in bud and with palate, the 2 lateral lobes narrower than the middle lobe and occurring in the same plane.

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