Herbs, annual, viscid pubescent to nearly glabrous, from slender or stout and ± woody taproots. Stems decumbent to semierect, unarmed, without glutinous bands on internodes. Leaves petiolate, unequal in size in each pair; blade ± thick and succulent, base usually asymmetric. Inflorescences axillary, pedunculate, capitate clusters; receptacle flat to somewhat rounded-conic, with short, pedicel-like projections; flowers maturing from one side of inflorescence to other; bracts persistent, not accrescent, 5–10, distinct, thin and translucent, forming an involucre, linear-lanceolate to ovate, broad. Flowers bisexual, chasmogamous; perianth radially symmetric, funnelform or salverform, constricted beyond ovary, abruptly expanded to 4–5-lobed limb; stamens (3–)4–5, included; styles included; stigmas linear. Fruits fusiform, indurate throughout, or spongy on exterior, minutely puberulent or glabrous; wings 2–4, translucent, prominently veined, scarious, extending beyond apex and/or base of body; sulci smooth or coarsely rugose.

Distribution

North America (including n Mexico).

Discussion

Species 4 (4 in the flora).

Selected References

Galloway, L. A. 1975. Systematics of North American desert species of Abronia and Tripterocalyx. Brittonia 27: 328–347.

Lower Taxa

Tripterocalyx carneus, Tripterocalyx crux-maltae, Tripterocalyx micranthus, Tripterocalyx wootonii

Key

1	Fruits usually with 2 wings, body occasionally ribbed laterally, extending prominently into wings	Tripterocalyx crux-maltae
1	Fruits usually with more than 2 wings, body often ribbed laterally, lateral ribs, if extending into wings, only slightly raised	> 2
2	Perianth tube 6-18 mm; perianth limb 3-5 mm diam., lobes inconspicous	Tripterocalyx micranthus
2	Perianth tube 12-30 mm; perianth limb 8-13 mm diam., lobes over 1.5 mm, showy	> 3
3	Perianth limb pale pink to magenta; fruits usually over 20 mm	Tripterocalyx carneus
3	Perianth limb white adaxially, white to pink abaxially; fruits usually 20 mm or less	Tripterocalyx wootonii