Herbs annual or biennial [perennial]; from taproot. Stems erect to ascending, [in O. pennellii very short and decumbent]. Flowers: buds nodding; floral tube erect, becoming recurved and nodding, then erect just before anthesis, 15–50 mm; petals broadly obovate to obcordate. Capsules usually straight, sometimes curved upward, cylindrical, sometimes slightly enlarged distally, subterete, 2–4[–5] mm diam. Seeds in 2 rows per locule, brown, sometimes dark-flecked, ellipsoid to subglobose, surface reticulate and regularly pitted. 2n = 14.

Species 4 (1 in the flora): sw, sc United States, Mexico, Central America (Guatemala), South America (Colombia, Ecuador, Peru).

Subsection Nutantigemma consists of four species and has one of the widest distributions in the genus, from Arizona and New Mexico to western Texas, southward nearly throughout Mexico to Guatemala; it is also in Andean Colombia, Ecuador, and Peru from 1500 to 3900 m (W. Dietrich 1977; Dietrich and W. L. Wagner 1988). The four species are likely self-compatible, but only two have been examined; of the two studied, one is a PTH species and the other is not.