Key to the genera of the Hiraea clade
1. Corolla nearly radial; petals pure white; connective of anthers flat and narrowly linear, hardly or not at all swollen abaxially; carpels connate their whole length in ovary; styles slender; sepals all eglandular; Mexico and northern Central America.
1. Corolla strongly bilateral; petals yellow or yellow and red or orange; connective of anthers abaxially broad and swollen; carpels distinct in ovary or nearly so; sepals all eglandular or 4 or all 5 bearing large abaxial glands; Mexico to South America, West Indies.
2. Bracteoles both eglandular.
3. Flowers borne ultimately in umbels of 4–many; abaxial sepal glands, if present, in pairs; stipules well developed, at least 1 mm long, often much longer.
3. Flowers borne ultimately in elongated pseudoracemes; abaxial sepal glands (rarely absent) 1 on each of the lateral sepals; stipules absent or vestigial, 0.2–0.5 mm long.
2. Bracteoles (1 of each pair) bearing 1 bulging eccentric abaxial gland.
4. Inflorescence an open, elongated, axillary or terminal panicle or pseudoraceme with the flowers borne singly or (most often) in 2s, 3s, or 4s; floriferous peduncles well developed; lateral wings of samara cleft to nut at apex and base.
4. Inflorescence a single axillary raceme of 3–7 (–9) 4-flowered umbels; floriferous peduncles short or absent; lateral wings of samara cleft to nut at apex but mostly continuous at base, only occasionally cleft to nut.