Nelsonia R.Br.

Scientific Description

Family Acanthaceae.

Habit and leaf form. Herbs (without cystoliths). Annual to perennial. Self supporting, or epiphytic, or climbing. Hydrophytic, or helophytic, or mesophytic, or xerophytic. Leaves opposite (decussate); petiolate to subsessile; 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. Leaf anatomy. Hairs present. 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 (with more or less spirally arranged overlapping bracts). The terminal inflorescence unit cymose, or racemose. Inflorescences terminal, or axillary. Flowers bracteate (intergrading with leaves); ebracteolate; somewhat irregular to very irregular; zygomorphic. The floral asymmetry involving the perianth. Flowers 4 merous, or 5 merous; tetracyclic. Free hypanthium absent. Hypogynous disk present. Perianth with distinct calyx and corolla; 9, or 10; 2 -whorled; isomerous, or anisomerous. Calyx 4, or 5 (the lobes 4, one usually notched at apex); 1 -whorled; gamosepalous; lobed; unequal but not bilabiate (unequal). Corolla 5; 1 -whorled; gamopetalous; contorted; tube slightly constricted at point of insertion of stamens; weakly bilabiate, or regular to unequal but not bilabiate (then with 5 subequal lobes). Androecium 2. Androecial members adnate; all equal; free of one another; 1 -whorled. Stamens 2. Staminal insertion in the throat of the corolla tube. Stamens all inserted at the same level; becoming exserted (slightly), or remaining included; reduced in number relative to the adjacent perianth; oppositisepalous; all alternating with the corolla members. Anthers dorsifixed; dehiscing via pores (pore at base, with small flap); bilocular; tetrasporangiate; unappendaged. 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; 1 - lobed, or 2 - lobed (lobes equal or unequal); wet type, or dry type; papillate, or non-papillate; Group II type, or Group III type. Placentation axile. Ovules 8–28 per locule; in 2–4 rows per locule; non-arillate, or arillate; hemianatropous, or anatropous, or campylotropous.

Fruit and seed features. Fruit non-fleshy; dehiscent; a capsule (conic, seed-bearing in basal portion). Capsules loculicidal. Fruit elastically dehiscent. Dispersal unit the seed. Fruit 8–28 seeded. Seeds globular; endospermic; tiny; not conspicuously hairy. Embryo well differentiated. Cotyledons 2. Embryo achlorophyllous; curved; large. Testa with numerous cristae. Seedling. Germination phanerocotylar.

Physiology, biochemistry. Aluminium accumulation not found.

Special features. The funicles not as in Acanthaceae. The upper (posterior, adaxial) lip of the corolla when bilabiate, bilobed. Lower (abaxial) lip of the corolla 3 lobed.

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 Fruit erostrate. Pollen grains colpate.