(Subfamily Byttnerioideae), Tribe Hermannieae.
Habit and leaf form. Herbs, or shrubs, or trees (rarely); non-laticiferous and without coloured juice. ‘Normal’ plants. Leaves well developed. Plants with roots; non-succulent. Leaves cauline. To 0.25–15 m high. Self supporting (or sprawling). Mesophytic. Not heterophyllous. Leaves small, or medium-sized; alternate; with blades; petiolate. Petioles wingless. Leaves with ‘normal’ orientation; simple; not peltate. Leaf blades neither inverted nor twisted through 90 degrees; dorsiventral; entire; flat; ovate; pinnately veined; cross-venulate. Mature leaf blades adaxially glabrous, or pubescent (sparsely); abaxially glabrous, or pubescent (sparsely). Leaves with stipules, or without stipules. Stipules intrapetiolar; free of the petiole; free of one another; spiny; persistent, or caducous (M. umbellata). Leaf blade margins entire, or serrate. Leaf anatomy. Hairs present; complex hairs present. Complex hairs stellate.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Plants homostylous.
Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; not crowded at the stem bases; in cymes, or in panicles. Inflorescences simple, or compound; terminal, or axillary. Flowers pedicellate; ebracteate; bracteolate. Bracteoles persistent, or deciduous. Flowers small; regular; not resupinate; neither papilionaceous or pseudo-papilionaceous; 5 merous; cyclic; tetracyclic. Floral receptacle with neither androphore nor gynophore. Perianth with distinct calyx and corolla; 10; 2 -whorled; isomerous. Calyx present; 5; 1 -whorled; gamosepalous; lobed. Calyx lobes markedly shorter than the tube, or about the same length as the tube, or markedly longer than the tube. Calyx hairy (rarely), or glabrous; exceeded by the corolla, or more or less equalling the corolla; campanulate; regular; neither appendaged nor spurred. Calyx lobes triangular. Epicalyx absent. Corolla present; 5; 1 -whorled; not appendiculate; polypetalous; white, or red, or pink, or purple, or yellow and orange (at centre); persistent. Petals spathulate. Androecium present. Fertile stamens present. Androecial members definite in number. Androecium 5, or 10. Androecial members free of the perianth; free of the gynoecium; markedly unequal; coherent (connate at the base, staminodes, if present, minute). The androecial groups opposite the petals. Androecial members 1 -whorled, or 2 -whorled. Androecium exclusively of fertile stamens, or including staminodes. Staminodes 5; non-petaloid. Stamens 5; all more or less similar in shape; isomerous with the perianth; alternisepalous; all opposite the corolla members; filantherous. Anthers separate from one another; all alike; dehiscing via longitudinal slits; bilocular. Fertile gynoecium present. Gynoecium 5 carpelled. The pistil 5 celled. Carpels isomerous with the perianth. Gynoecium syncarpous; synovarious, or synstylovarious, or eu-syncarpous; superior. Ovary plurilocular; 5 locular; sessile, or stipitate (glabrous to densely hairy). Gynoecium stylate. Styles 5; free, or partially joined; apical. Stigmas 5 (connate at base). Placentation axile. Ovules 2 per locule.
Fruit and seed features. Fruit 1–6 mm long; hairy, or not hairy; dehiscent; a capsule. Capsules septicidal (M. corchorifolia), or loculicidal. Dispersal unit the seed.
Geography, cytology, number of species. Native of Australia, or adventive. Not endemic to Australia. Australian states and territories: Western Australia, Northern Territory, and Queensland. Northern Botanical Province. A genus of ca 75 species; 3 species in Western Australia; 0 endemic to Western Australia.