Rev. Gén. Bot. 20: [358-]359, fig. 1. 1908.
Vines, twining, wiry, slender, with woody base, sometimes seeming shrubby when grazed. Leaves usually bearing pair of stalked glands or eglandular processes on blade margin near base; stipules interpetiolar, distinct. Inflorescences terminal on lateral shoots, 2–4-flowered umbels. Pedicels raised on peduncles. Flowers all chasmogamous, 6+ mm diam., showy with visible petals, stamens, and styles; calyx glands usually 8 (anterior sepal usually eglandular, 4 lateral usually 2-glandular); corollas bilaterally symmetric, petals lemon yellow, glabrous; stamens (4–)5, 2 fertile, opposite posterior-lateral sepals, [0–](2–)3 staminodial, opposite anterior and anterior-lateral sepals, (staminodial filaments rudimentary); fertile anthers subequal, staminodial anthers absent; pistil 3-carpellate, carpels completely connate in ovary; style 1, borne on anterior carpel, cylindric; stigma terminal, capitate [truncate], large. Fruits schizocarps, breaking into 3 samaras; samaras bearing 1 elongate dorsal wing thickened on adaxial edge, veins bending toward thinner abaxial edge, lateral wings absent; nut reticulate and often parallel-rugose on sides, wall thick, tough. x = 10.
sw United States, n Mexico.
Species 3 (1 in the flora).