Microcarpaea might be better combined with its close ally Peplidium, but investigation of the pollen shows it to be unique in the family by its many operculate pores. This combined with the distinctive calyx indicates that retention of generic status is the best present course (Wheeler et al, (1992).
Habit and leaf form. Herbs. Annual, or perennial; plants with a basal concentration of leaves, or with neither basal nor terminal concentrations of leaves. Helophytic, or mesophytic, or xerophytic. Leaves minute to small; opposite; ‘herbaceous’, or leathery, or membranous; petiolate to sessile; connate; simple; epulvinate. Leaf blades entire; oblong, or elliptic; pinnately veined. Mature leaf blades adaxially pubescent; abaxially pubescent. Leaves without stipules. Leaf blade margins entire. 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 solitary; axillary; more or less sessile; bracteate; ebracteolate; minute to small; very irregular; zygomorphic; 5 merous; tetracyclic. Free hypanthium absent. Hypogynous disk present. Perianth with distinct calyx and corolla; 10; 2 -whorled; isomerous. Calyx present; 5; 1 -whorled; gamosepalous; lobed. Calyx lobes markedly shorter than the tube. Calyx spreading; imbricate, or valvate; tubular; regular; persistent; with the median member posterior. Calyx lobes triangular. Corolla present; 5; 1 -whorled; gamopetalous; lobed; lobulate and toothed. Corolla lobes markedly shorter than the tube and about the same length as the tube. Corolla imbricate, or valvate; bilabiate. Androecium 2. Androecial members adnate (to the corolla); all equal; free of one another; 1 -whorled. Stamens 2; all inserted at the same level; remaining included; all more or less similar in shape; reduced in number relative to the adjacent perianth; oppositisepalous. Anthers all alike; centrifixed; dehiscing via longitudinal slits; introrse; unilocular; tetrasporangiate. Gynoecium 2 carpelled. The pistil 2 celled. Gynoecium non-petaloid; syncarpous; 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 (a broad flap covering the mouth of corolla, receptive above, probably irritable); 1 - 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; not hairy; not spinose; 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. Cotyledons 2. Embryo straight to curved.
Special features. Corolla tube not exceeding the calyx; straight. The upper lip of the corolla incorporating 2 members, the lower 3; (posterior, adaxial) lip of the corolla bilobed (lobes tiny). Lower (abaxial) lip of the corolla 3 lobed.
Geography, cytology, number of species. Native of Australia. Not endemic to Australia. Australian states and territories: Western Australia and Northern Territory. Northern Botanical Province.
Etymology. From the Greek for "small" and "fruit".
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Western Australian Herbarium (1998–). FloraBase—the Western Australian Flora. Department of Biodiversity, Conservation and Attractions. https://florabase.dpaw.wa.gov.au/