Annual much-branched herbs, more or less pubescent with flattened hairs, with opposite, usually unequal leaves, and axillary or lateral long-peduncled involucres subtending numerous pink or whitish flowers, the involucral bracts separate. Perianth-tube elongated, the limb 5-lobed. Stamens 5, inserted on the perianth-tube; filaments short. Fruit dry, leathery, completely encircled by 2 to 4 broad reticulated membranous wings. [Greek, three-winged calyx.]

About 5 species, natives of western North America, the following the generic type.

3 Tripterocalyx Torr Hook Kew Journ Bot 5 261 1853 74

1. Tripterocalyx Micránthus (Torr.) Hook. Pink Abronia

Fig. 1732

Tripteridium micranthum Torr. Frem. Rep. 96. 1845.

Abronia micrantha Chois. in DC. Prodr. 13: Part 2, 436. 1849.

Tripterocalyx micranthus Hook. Kew Journ. Bot. 5: 261. 1853. [By typographical error macranthus.]

Annual, glabrous below, more or less glandular-pubescent above, stem ascending, branched, 1°-2° high. Leaves quite similar to those of Abronia fragrans in size and outline; involucral bracts ovate or ovate-lanceolate, acute or acuminate; flowers several or numerous, about 6" long, greenish-white; calyx-limb about 4" broad; fruit nearly 1' high, its 2-4 membranous wings 4"-7" broad, entire-margined, shining, very conspicuous, glabrous, united over the body of the fruit, beautifully reticulate-veined.

In dry soil, South Dakota to Montana, Nevada, Kansas and New Mexico. June-Aug.