Syst. Nat. ed. 10, 2: 890. 1759.
Herbs, annual or perennial, finely pubescent, often somewhat viscid; taproot slender and soft to stout and woody (depending on duration). Stems procumbent, often clambering through other vegetation, unarmed, without glutinous bands on internodes. Leaves paired, petiolate, unequal, blades thin, base ± asymmetric. Inflorescences axillary, pedunculate, clusters of 3 simultaneously blooming flowers resembling single flower; bracts persistent, not accrescent, 3, forming involucre, distinct, broadly ovate, cucullate, thin, translucent. Flowers bisexual, chasmogamous; perianth strongly bilaterally symmetric, funnelform but strongly oblique, constricted beyond ovary, gradually expanded, adaxial lobes minute, abaxially forming a fan-shaped limb; stamens 4–7, ± exserted; styles exserted beyond stamens; stigmas capitate. Fruits oblong to somewhat obovate, dorsoventrally compressed (adaxial face convex, internal, in inflorescence), with 5 strongly modified ribs, central adaxial rib an inconspicuous to pronounced rib or ridge, sometimes toothed, keeled, coriaceous; 2 lateral ribs expanded and incurved toward concave side as wings or teeth; 2 ribs on concave surface forming low, thin ridge, often with teeth that usually bear glands at tip, surface glabrous, and smooth or the adaxial slightly rugose.
sw United States, Mexico, Central America, West Indies, South America
Species 2 (2 in the flora).
The two species of Allionia are very similar, differing primarily in the nature and number of teeth on the fruit. In many floras for areas south of the United States only a single species, Allionia incarnata, is recognized. When sympatric, the two species are distinguishable by vegetative and perianth features, but throughout their ranges, the two species cannot be consistently distinguished by the same characteristics. Nevertheless, as noted by B. L. Turner (1994), plants with intergradient fruits are uncommon. Both species may produce fruits with lateral ribs that are curved and winglike, without teeth; this condition is frequent in A. incarnata in North America and occasional in A. choisyi in South America.
The three bilaterally symmetric flowers in the Allionia inflorescence bloom synchronously and are sufficiently closely situated that the entire inflorescence resembles a single radially symmetric flower. The fruit is among the most complex in the family. The convex side, oriented toward the center of the cluster of three flowers, exudes copious mucilage when wetted. The viscid glands on the concave surface remain sticky for decades in the herbarium.
|1||Fruits deeply convex adaxially; lateral ribs developed as curved wings with 0-4 irregular or regular triangular teeth; viscid glands on concave side on stalks usually equaling or shorter than diameter of glandular head||Allionia incarnata|
|1||Fruits shallowly convex adaxially; lateral ribs developed as curved wings with 4-8 slender teeth; viscid glands on concave side on stalks usually equaling or longer than diameter of glandular head||Allionia choisyi|
"thin" is not a number.