Common name. Malvastrums. Family Malvaceae.
Habit and leaf form. Shrubs, or herbs (usually with a dense stellate-hairy or tomentose indumentum). Plants unarmed. Annual, or perennial; to 0.5–2 m high. Mesophytic. Not heterophyllous. Leaves medium-sized; alternate; spiral; petiolate; non-sheathing; simple. Leaf blades dorsiventral; entire (mostly), or dissected; ovate; pinnately veined, or palmately veined; cordate, or cuneate at the base (or truncate). Mature leaf blades adaxially pubescent, or woolly; abaxially pubescent, or woolly. Leaves with stipules (stipules linear or ovate or triangular). Stipules caducous, or persistent. Leaf blade margins coarsely crenate, or serrate, or dentate. Leaf anatomy. Hairs present; complex hairs present. Complex hairs stellate. Extra-floral nectaries absent.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Entomophilous.
Inflorescence and flower features. Flowers solitary, or aggregated in ‘inflorescences’; axillary; in racemes, or in spikes, or in panicles. Inflorescences terminal, or axillary; inflorescence of solitary or clustered axillary flowers, or terminal or axillary spikes or racemes. Flowers shortly pedicellate, or sessile; small; regular; 5 merous; tetracyclic. Hypogynous disk absent. Perianth with distinct calyx and corolla; 10; 2 -whorled; isomerous. Calyx present; 5; 1 -whorled; gamosepalous; lobed; lobulate (5-lobed). Calyx lobes about the same length as the tube to markedly longer than the tube. Calyx hairy; valvate; slightly exceeded by the corolla; campanulate; regular. Calyx lobes ovate, or triangular. Epicalyx present (of small free bracteoles). Corolla present; 5; 1 -whorled; polypetalous (adnate to the base of the staminal column); imbricate; yellow, or orange, or red. Petals clawed (short). Androecium present. Androecial members indefinite in number. Androecium 50–100 (i.e. ‘many’). Androecial members adnate; all equal; coherent (connate; the filaments fused in a column surrounding the style); 1 - adelphous (the tube attached to the petals); 1 -whorled. Androecium exclusively of fertile stamens (or rather, half-stamens, each having only a half anther). Stamens 50–100. Anthers dehiscing via longitudinal slits; introrse; unilocular. Gynoecium 5–18 carpelled (in a single whorl). The pistil 5–18 celled. Gynoecium syncarpous; synstylovarious to eu-syncarpous; superior. Ovary plurilocular; 5–18 locular. Gynoecium stylate. Styles 1; more than 4-branched (5–18, i.e. as many as the carpels); apical. Stigmas 5–18 (connate towards the base); capitate. Placentation axile. Ovules 1 per locule.
Fruit and seed features. Fruit non-fleshy; hairy; a schizocarp (discoid, separating septicidally into indehiscent mericarps leaving a persistent cental axis). Mericarps 5–18; comprising achenes, or comprising follicles. Dispersal unit the mericarp (laterally compressed, reniform in outline, sometimes awned). Seeds 1 per mericarp. Seeds small; not conspicuously hairy.
Geography, cytology, number of species. World distribution: pantropical. Native of Australia. Not endemic to Australia. Australian states and territories: Western Australia, South Australia, Northern Territory, Queensland, New South Wales, Victoria, and Australian Capital Territory. Northern Botanical Province. 2n = 24 for M. americanum, M. bicuspidatum, M. amblyphyllum, M. tomentosum and M. coromandelianum; 2n = 36 for M. aurantiacum and M. interrptum; 2n = 48 for M. corchorifolium and M. scoparioides. A genus of c. 12 species; 2 species in Western Australia; 0 endemic to Western Australia.
Additional comments. Etymology: derived from malva, the generic name for true mallows and from the Latin -astrum which indicates an incomplete resemblance.
Etymology. From genus Malva and the Latin -aster (-like, but implying incomplete likeness or inferiority).