Key to the genera of the Christianella clade
1. Sepals bearing a row of small marginal glands, these sessile or subsessile to long-stalked, clavate or capitate.
1. Sepals without marginal glands.
2. Bracteoles globose-cymbiform, one overlapping the other and the pair completely enclosing and hiding sepals and petals in enlarging bud;
pedicel 0–2 mm long, up to 5 mm long in fruit.
2. Bracteoles various but not enclosing or hiding sepals and petals in bud; pedicel well-developed, longer than 2 mm, often much longer.
3. Lamina glands strictly marginal.
4. Sepals (the lateral 4) bearing 8 large abaxial glands; corolla bilaterally symmetrical; petals yellow, exposed in enlarging bud;
Texas and Mexico to South America.
4. Sepals all eglandular; corolla radially symmetrical; petals white, hidden by sepals in enlarging bud; Africa.
3. Lamina glands borne impressed in abaxial surface, set in from margin.
5. Sepals not completely concealing petals during enlargement of bud; each lateral wing of samara containing in its base a sterile cavity parallel to the fertile locule.
5. Sepals completely concealing petals during enlargement of bud; lateral wings of samara without sterile cavities.
6. Petals white, white and pink, pink, or lilac, abaxially densely tomentose or subsericeous; inflorescence paniculate with the flowers borne in short to elongated pseudoracemes; lateral 4 sepals abaxially biglandular, the anterior usually eglandular.
6. Petals yellow turning red in age, glabrous; inflorescence dichasial with the flowers borne in pairs or umbels or corymbs of 4 (–8); all 5 sepals abaxially biglandular.