Dicladanthera F.Muell.

Scientific Description

Family Acanthaceae.

Habit and leaf form. Spreading herbs, or shrubs (subshrubs, with cystoliths). The herbs perennial. Young stems 6-angled. Hydrophytic, or helophytic, or mesophytic, or xerophytic. Leaves opposite (each pair connected by a transverse ridge); petiolate to 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; flat. Leaf anatomy. Hairs present, or absent. 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 solitary, or aggregated in ‘inflorescences’. The terminal inflorescence unit cymose, or racemose. Inflorescences axillary; a long-pedunculate group of 1–5 flowers at different developmental stages, subtended by 2 free outer bracts; pseudanthial, or not pseudanthial. Flowers 2–5- bracteolate; regular, or somewhat irregular (rarely); when irregular, zygomorphic. The floral asymmetry involving the perianth (K only). Flowers 5 merous; tetracyclic. Free hypanthium absent. Hypogynous disk present; annular. Perianth with distinct calyx and corolla; 10; 2 -whorled; isomerous. Calyx 5 (shorter and thinner than bracts and bracteoles); 1 -whorled; gamosepalous (free almost to base), or partially gamosepalous (sometimes 2 members fused for 1/4 to 3/4 of their length, the others free); lobed; with the median member posterior. Corolla 5; 1 -whorled; gamopetalous; imbricate, or contorted, or with open aestivation; with short narrow tube about ovary, widening into much larger throat; regular. Androecium 2. Androecial members adnate; all equal; free of one another; 1 -whorled. Stamens 2. Staminal insertion in the throat of the corolla tube (with long rib decurrent below). Stamens reduced in number relative to the adjacent perianth; oppositisepalous; all alternating with the corolla members. Filaments short, divided at apex into a U-shaped connective perpendicular to filament, the 2 parallel arms each terminated by an anther cell. Anthers dorsifixed; dehiscing via longitudinal slits; 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 (forked); when simple, capitate; 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; hairy, or not hairy; dehiscent; a capsule (clavate, seed-bearing in upper half). Capsules loculicidal. Fruit elastically dehiscent. Dispersal unit the seed. Fruit 2–4 seeded. Seeds discoid; non-endospermic; small; 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’).

Geography, cytology, number of species. Native of Australia. Endemic to Australia. Australian states and territories: Western Australia. Eremaean Botanical Province.