Hooker’s J. Bot. Kew Gard. Misc. 5: 261. 1853.
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.
North America (including n Mexico).
Species 4 (4 in the flora).
|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|