Isotropis Benth.

Scientific Description

Family Papilionaceae. Mirbelieae.

Sometimes included in Leguminosae.

Habit and leaf form. (Under-) shrubs, or herbs. ‘Normal’ plants to switch-plants (see Crisp and Weston, 1995); at least sometimes partially phyllodineous (cf. Crisp and Weston, 1995). Plants unarmed. Leaves alternate; ‘herbaceous’; petiolate to sessile; non-sheathing; simple (or ‘articulate’), or compound (then ostensibly simple); pulvinate, or epulvinate; if ‘compound’, unifoliolate. Leaflets 1; not stipellate. Leaves with stipules. Stipules intrapetiolar; free of one another; scaly, or leafy (linear or ovate, sometimes minute).

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Entomophilous.

Inflorescence and flower features. Flowers solitary, or aggregated in ‘inflorescences’; when solitary, axillary; 1 per axil (long pedicellate); when aggregated, in racemes. Inflorescences simple. The terminal inflorescence unit racemose. Inflorescences terminal. Flowers long pedicellate; bracteolate; very irregular; zygomorphic. The floral asymmetry involving the perianth, or involving the perianth and involving the androecium. Flowers papilionaceous; tetracyclic. Floral receptacle with neither androphore nor gynophore. Free hypanthium present, or absent. Hypogynous disk present; intrastaminal; annular. Perianth with distinct calyx and corolla; 10; 2 -whorled; isomerous. Calyx present; 5; 1 -whorled; gamosepalous; five lobed. Calyx lobes markedly longer than the tube. Calyx imbricate; exceeded by the corolla; bilabiate (the posterior members connate almost to their tips); non-fleshy; persistent; non-accrescent; with the median member anterior. Corolla present; 5; 1 -whorled; appendiculate, or not appendiculate. Standard not appendaged. Corolla partially gamopetalous. 2 of the petals joined. The joined petals anterior (the keel members). The wings of the corolla free from the keel; not laterally spurred. Standard ‘normally’ developed; entire, or emarginate. Keel about equalling the wings (incurved); not long-acuminate/beaked; neither coiled nor spiralled; not bent and beaked. Corolla imbricate; yellow, or red, or yellow and red, or purple; deciduous; non-accrescent. Petals shortly clawed. Androecial members definite in number. Androecium 10. Androecial sequence determinable, or not determinable. Androecial members free of the perianth; markedly unequal; free of one another; 1 -whorled. Androecium exclusively of fertile stamens. Stamens 10; all more or less similar in shape; diplostemonous; both opposite and alternating with the corolla members; filantherous. Anthers separate from one another to connivent; all alike; dorsifixed; versatile; dehiscing via longitudinal slits; latrorse, or introrse; tetrasporangiate. Gynoecium 1 carpelled. The pistil 1 celled. Carpels reduced in number relative to the perianth. Gynoecium monomerous; of one carpel; superior. Carpel stylate. Style (in-) curved (filiform). Style glabrous. Stigmatic tissue terminal. Carpel 7–25 ovuled (? — ‘numerous’). Placentation marginal. Stigmas truncate (‘minute’). Ovules slenderly funicled; biseriate.

Fruit and seed features. Fruit non-fleshy. The fruiting carpel dehiscent; a legume. Pods much elongated (narrowly oblong to narrowly obovate in outline); not triangular; straight; becoming inflated, or not becoming inflated; somewhat compressed, or terete (‘more or less turgid’); not constricted between the seeds; not transversely septate; wingless. Fruit 1 celled. Dispersal unit the seed. Seeds not mucous; non-arillate. Embryo bent (radicle inflexed). Testa non-operculate.

Geography, cytology, number of species. Native of Australia. Endemic to Australia. A genus of 10–11 species; 10 species in Western Australia.