Centranthera R.Br.

Scientific Description

Family Scrophulariaceae.

Habit and leaf form. Herbs. ‘Normal’ plants, or plants of very peculiar form (parasitic). Partially parasitic. On roots of the host. Annual; plants with a basal concentration of leaves, or with neither basal nor terminal concentrations of leaves; to 0.55 m high. Helophytic, or mesophytic, or xerophytic. Leaves small to medium-sized; opposite, or alternate and opposite (alternate above); when alternate spiral, or four-ranked; ‘herbaceous’, or leathery, or membranous; sessile; sheathing, or non-sheathing; simple; epulvinate. Leaf blades entire; linear, or ovate; pinnately veined. Mature leaf blades adaxially scabrous, or pubescent; abaxially scabrous, or pubescent. Leaves without stipules. Leaf blade margins entire, or dentate. Leaves without a persistent basal meristem. Leaf anatomy. Hydathodes present (occasionally), or absent. Hairs present; glandular 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 aggregated in ‘inflorescences’; in racemes. The terminal inflorescence unit cymose, or racemose. Inflorescences terminal, or axillary; spike-like. Flowers pedicellate to sessile; bracteate; bracteolate; small to medium-sized; somewhat irregular, or very irregular; zygomorphic; tetracyclic. Free hypanthium absent. Hypogynous disk present. Perianth with distinct calyx and corolla; 7–10; 2 -whorled; isomerous, or anisomerous. Calyx present; 2–5 (sometimes entire); 1 -whorled; gamosepalous (and split down abaxial side); 2–5 lobed, or entire; toothed. Calyx lobes markedly shorter than the tube. Calyx erect; imbricate, or valvate. Degree of gamosepaly, maximum length joined/total calyx length 1. Calyx unequal but not bilabiate, or bilabiate, or regular; persistent; accrescent, or non-accrescent; when K5, with the median member posterior. Corolla present; 5; 1 -whorled; gamopetalous. Corolla lobes markedly shorter than the tube. Corolla imbricate, or valvate; tube dilated from point of exsertion from calyx; regular, or bilabiate; glabrous abaxially; glabrous adaxially; plain, or with contrasting markings; white, or pink, or purple. Androecium 4. Androecial members adnate (to the corolla); markedly unequal; coherent; 1 -whorled. Stamens 4. Staminal insertion near the base of the corolla tube. Stamens remaining included; didynamous; reduced in number relative to the adjacent perianth; oppositisepalous. Filaments hairy. Anthers cohering (in pairs); dehiscing via longitudinal slits; introrse; bilocular (cells confluent, distally awned, 1 cell sometimes smaller than the other and then sometimes empty); tetrasporangiate. Gynoecium 2 carpelled. The pistil 2 celled. Gynoecium non-petaloid; syncarpous; synstylovarious to 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. Stigmas 1; 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 (with the septum remaining attached to the 2 valves). Fruit 50 seeded (to ‘many’). Seeds endospermic. Endosperm oily. Seeds minute; wingless (and twisted). Cotyledons 2. Embryo straight to curved.

Special features. Corolla tube exceeding the calyx; straight, or curved. The upper lip of the corolla incorporating 2 members, the lower 3; (posterior, adaxial) lip of the corolla bilobed. Lower (abaxial) lip of the corolla 3 lobed.

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

Etymology. From the Greek for "point, spike" and "anther"; the anthers have awn-like points.