Nuovo Giorn. Lett., Sci. 24: 145
Annual herb, roots fibrous. Tufted with stems 20–30 mm long and densely covered with leaf bases and appearing almost stemless, or stems evident and to 80 mm long, with or without side branches, not rooting at nodes. Stems sparsely hirsute, green or reddish at base; bulbils absent. Leaves cauline, alternate, 3-foliolate; leaflets subsessile, obcordate, 5–20 mm long, 5–20 mm wide, bilobed, green, upper leaf surface lightly covered with ascending to suberect erect, more densely hairy below, margins ciliate, sinus to c. one-quarter leaflet length, lobes obovate or suborbicular, apices rounded; petioles usually 4–10 cm long, with mostly spreading hairs; stipules conspicuous, to 9 mm long, widened at base, with scattered hairs on outer surface. Inflorescences axillary, raceme-like, flowers usually 4–14 per peduncle usually held above leaf level; peduncles usually longer than leaves, with spreading hairs; pedicels often recurved. Sepals linear-lanceolate, 2–4 mm long, usually with red margins, and with two basal reddish-purple blotches on either side of sepal, sparsely hirsute; petals 2.5–4 mm long, slightly longer than calyx, yellow. Styles short. Capsule oblong, 2.5–4 mm long, 1–2 mm diam., glabrous, seeds many per capsule; seeds 0.7–0.8 mm long, more or less spherical, apiculate at each end, transversely ribbed, ribs 5–7 (often broken), uniformly brown, dull. (Description based on Australian plants). Flowers Oct. (2 collections).
Currently known only from Victoria, where first collected in 2016, at Plenty Gorge Park (north-eastern outskirts of Melbourne). Native to Argentina, Chile and Peru. Naturalised in Ecuador, and California. At Plenty Gorge Park, Oxalis micrantha is abundantly naturalised along walking track in Eucalyptus melliodora woodland, and in disturbed area adjacent to Eucalyptus leucoxylon subsp. connata woodland.
Other than some forms of Oxalis corniculata, O. micrantha is the only other annual member of the genus in Australia. The habit of the species varies significantly depending on the ecological conditions. Plants in drier sites can be much reduced in habit, appearing almost stemless.