Mirbelia Sm.

Scientific Description

Family Papilionaceae. Mirbelieae.

Sometimes included in Leguminosae.

Habit and leaf form. Shrubs. ‘Normal’ plants, or switch-plants; with the principal photosynthesizing function transferred to stems. Leaves well developed, or much reduced (to scales, e.g. M. ramulosa), or absent. Plants prickly (via the leaves), or spiny (e.g. M. spinosa, with branchlets reduced to spines), or unarmed. Leaves cauline. Plants with neither basal nor terminal concentrations of leaves. Leaves alternate, or opposite, or whorled; petiolate, or subsessile, or sessile; non-sheathing; simple; epulvinate. Leaf blades dissected, or entire. Leaves with stipules, or without stipules. Stipules when present, intrapetiolar (small); free of one another; setaceous. Leaf blade margins prickly (leaves punbent tipped in M. floribunda, pungently lobed in M. dilatata), or not prickly.

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

Inflorescence and flower features. Flowers solitary, or aggregated in ‘inflorescences’; when solitary terminal, or axillary; in racemes, or in fascicles. Inflorescences simple. The terminal inflorescence unit racemose. Inflorescences terminal, or axillary. Flowers pedicellate to subsessile; bracteate, or ebracteate; bracteolate, or ebracteolate. Bracteoles persistent, or deciduous. Flowers very irregular; zygomorphic; papilionaceous; tetracyclic. Floral receptacle developing a gynophore (usually), or 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; imbricate, or valvate; bilabiate (the two posterior lobes generally broader and more connate); non-fleshy; persistent; non-accrescent; with the median member anterior. Corolla present; 5; 1 -whorled; appendiculate, or not appendiculate. Standard not appendaged. Corolla polypetalous, or partially gamopetalous. 2 of the petals joined (the keel members). The joined petals anterior. The wings of the corolla free from the keel; not laterally spurred. Standard ‘normally’ developed; entire, or emarginate. Keel conspicuously exceeded by the wings (usually), or about equalling the wings (broader than them); not long-acuminate/beaked; neither coiled nor spiralled; not bent and beaked. Corolla imbricate; yellow, or red, or pink, or purple (or reddish-purple), or violet, or blue, or brown (in various combinations, the standard often with an ‘eye’); deciduous. Petals clawed. Androecial members definite in number. Androecium 10. Androecial sequence determinable, or not determinable. Androecial members free of the perianth; all equal, or 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; dehiscing via longitudinal slits; latrorse, or introrse; tetrasporangiate. Gynoecium 1 carpelled. The pistil 2 celled (with a spurious septum intruded from the abaxial suture). Carpels reduced in number relative to the perianth. Gynoecium monomerous; of one carpel; superior. Carpel stylate. Style (in-) curved (and filiform), or hooked (then short and thick). Style glabrous. Stigmatic tissue terminal. Carpel 2–15 ovuled (? — ‘2 or more’). Placentation marginal. Stigmas capitate. Ovules slender funicled; biseriate.

Fruit and seed features. Fruit stipitate, or subsessile; non-fleshy. The fruiting carpel dehiscent; a legume (the endocarp and epicarp usually separating). Pods globose to much elongated (ovoid, oblong or cylidrical); not triangular; straight; becoming inflated, or not becoming inflated; somewhat compressed, or terete (‘turgid’); not constricted between the seeds; not transversely septate; wingless. Fruit 2 celled. Dispersal unit the seed. Fruit 2–15 seeded. Seeds not mucous; non-arillate. Embryo bent (radicle inflexed). Testa non-operculate.

Geography, cytology, number of species. Native of Australia. Endemic to Australia. 2n = 16. A genus of 22–224 species; 22 species in Western Australia.