Description: Herbs or subshrubs, erect or spreading, annual or (rarely, not in N.S.W.) perennial, with a thin or (rarely) thickened taproot, occasionally rhizomatous. Indumentum of stalked or sessile glandular hairs, often dense, occasionally plants mostly glabrous.
Leaves cauline, usually dark green, palmately compound with 1–7(–9) leaflets, the central leaflet usually larger; uppermost leaves often 1 -foliate or simple, becoming bract-like; petiolate; lateral venation obscure or with 2–9 distinct veins per side; stipules absent.
Flowers ± actinomorphic or zygomorphic, 4-merous, diminutive to showy, usually not exceeding the leaves unless in a bracteate raceme. Sepals in 2 whorls of 2, green or purple, without distinct, darker venation. Petals 4, arranged in an X, with 2 held erect and 2 pointing down, or all held erect to varying degrees, predominantly yellow, often with red or purple markings on the claw, occasionally maroon, without distinct, darker venation; clawed or not. Stamens 1–52, usually ± free, occasionally connate in the lower half and adnate to the gynophore, forming an androgynophore (A. cleomoides and A. kenneallyi, not in N.S.W.); filaments uniformly cream, yellow, or rarely purple; anthers straight or curved to revolute, greenish-yellow, basifixed. Gynophore usually absent or < 5 mm long (conspicuous, 45–64 mm long in A. cleomoides, not in N.S.W.). Ovary usually green, cylindric. Style shorter than or exceeding stamens, sometimes dimorphic in length within a species, stigma usually yellow, linear.
Fruit a capsule, erect to pendulous, pedicellate, very narrowly cylindric to ovoid, often slightly curved, usually longitudinally striate, sometimes smooth; beak somewhat fragile. Seeds 3-numerous, brown to black, suborbicular, asymmetrical, curved with an open or closed cleft; surface usually prominently and regularly transversely ridged; eliosome usually present, occasionally absent, white to cream.
Distribution and occurrence: Endemic to Australia, except A. viscosa, which naturally extends through southeast Asia to India and North Africa, and is introduced to Central America, including the Galapagos Is. Australia: 13 species currently described, W.A., Cocos Is., Christmas Is. (native and naturalised), Ashmore Reef, N.T. (native and naturalised), Qld. (native and naturalised), NSW (naturalised).
Text by Kerry Gibbons 15 May 2023, adapted from Barrett et al. 2017.
Taxon concept: Barrett et al. 2017 Syst. Bot. 42: 694-708.
| One species in NSW: Arivela viscosa |
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