Habit and leaf form. Herbs. Plants more or less succulent, or non-succulent. Annual, or perennial. Leaves cauline. Plants with neither basal nor terminal concentrations of leaves. Young stems tetragonal. To 0.35 m high. Hydrophytic, or helophytic; when hydrophytic, rooted. Leaves of aquatics floating. Heterophyllous, or not heterophyllous. Leaves minute to medium-sized; opposite; ‘herbaceous’, or leathery, or membranous; petiolate to sessile; simple; epulvinate. Leaf blades dissected, or entire; ovate, or obovate, or oblong, or elliptic; if dissected pinnatifid, or much-divided; pinnately veined, or palmately veined; cordate, or attenuate at the base. Mature leaf blades adaxially glabrous; abaxially glabrous. Leaves without stipules. Leaf blade margins entire to dentate. Leaves without a persistent basal meristem. Leaf anatomy. Hydathodes present (occasionally), or absent. Hairs absent. Stem anatomy. Secondary thickening developing from a conventional cambial ring.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Entomophilous.
Inflorescence and flower features. Flowers solitary, or aggregated in ‘inflorescences’; axillary. The terminal inflorescence unit cymose, or racemose. Inflorescences of solitary or paired flowers in leaf axils, so numerous that the plant often appears like a leafy raceme or panicle. Flowers pedicellate; bracteate; bracteolate, or ebracteolate; small; more or less regular, or very irregular; zygomorphic; 4–5 merous; tetracyclic. Free hypanthium absent. Hypogynous disk present. Perianth with distinct calyx and corolla; 9, or 10; 2 -whorled; isomerous, or anisomerous. Calyx present; 5; 1 -whorled; polysepalous, or gamosepalous (at base only); lobed (lobes unequal, 3 outer broad, 2 inner narrow). Calyx lobes markedly longer than the tube. Calyx erect; imbricate. Degree of gamosepaly, maximum length joined/total calyx length less than 0.25. Calyx unequal but not bilabiate; persistent; accrescent; with the median member posterior. Sepals ovate, or triangular. Calyx lobes ovate, or triangular. Corolla present; 4 (the posterior pair united), or 5; 1 -whorled; gamopetalous; lobed; imbricate, or valvate; campanulate; more or less regular, or bilabiate; glabrous abaxially; glabrous adaxially; plain, or with contrasting markings; white, or purple, or blue. Androecium 4. Androecial members adnate (to the corolla); all equal, or markedly unequal; free of one another; 1 -whorled. Stamens 4; didynamous; reduced in number relative to the adjacent perianth, or isomerous with the perianth; oppositisepalous. Anthers dehiscing via longitudinal slits; introrse; bilocular (cells separate but not stipitate); tetrasporangiate. Gynoecium 2 carpelled. The pistil 2 celled. Gynoecium non-petaloid; syncarpous; eu-syncarpous; superior. Ovary plurilocular; 2 locular. Gynoecium median; stylate. Styles 1; attenuate from the ovary, or from a depression at the top of the ovary; apical; persistent. Stigmas 1; 2 - lobed. Placentation axile, or apical. Ovules 50 per locule (to ‘many’); pendulous to ascending; non-arillate; anatropous, or campylotropous, or hemianatropous.
Fruit and seed features. Fruit non-fleshy; dehiscent; a capsule. Capsules loculicidal, or septicidal and loculicidal (then secondarily loculicidal), or valvular. Fruit 50 seeded (to ‘many’). Seeds endospermic. Endosperm oily. Seeds minute. Cotyledons 2. Embryo straight to curved.
Special features. Corolla tube straight. The upper lip of the corolla incorporating 2 members, the lower 3; (posterior, adaxial) lip of the corolla entire, or bilobed. Lower (abaxial) lip of the corolla 3 lobed.
Geography, cytology, number of species. Holarctic, Paleotropical, Neotropical, Cape, and Australian. Native of Australia. Not endemic to Australia. Australian states and territories: Western Australia, Northern Territory, Queensland, and New South Wales. Northern Botanical Province.
Etymology. The name of the plant in Guiana.