1. Mentzelia L. (stickleaf, blazing star)

Plants biennial or perennial herbs (annuals elsewhere). Stems branched, brittle, often whitish. Leaves usually alternate, simple, the petioles short and pubescent. Stipules absent. Leaf blades pinnately veined and lobed, with abundant minute barbed hairs. Inflorescences terminal, few-flowered clusters or solitary, these apparently arranged into small racemes or panicles. Flowers actinomorphic, perfect, epigynous. Sepals 5, sometimes persistent in fruit. Petals 5 or apparently 10 (including 5 petaloid staminodes), whitish yellow to deep orange. Stamens numerous, the filaments sometimes unequal, shorter toward flower center, fused together basally and to the petal bases, sometimes expanded and petaloid. Pistil of 3 fused carpels. Ovary inferior, with 1 locule, the placentation parietal, the ovules numerous. Styles 3, united most of their length, filiform, the stigmas represented by 3 furrows or tufts of hairs. Fruits capsules, more or less cylindrical, densely pubescent with minute barbed hairs, dehiscent by an apical valve. Seeds few to numerous, elongate and prismatic or flattened and winged. About 60 species, primarily in the southwestern U.S. and Mexico, a few species in Argentina and the Bahamas.

Sections within Mentzelia are distinguished by characters of the filaments, seeds, and placentae. In Missouri, the common native species M. oligosperma belongs to section Mentzelia, and the two introduced species belong to section Bartonia Torr. & A. Gray, which at one time was recognized as a separate genus (Darlington, 1934). Additional characters are found in the number of petals and petaloid staminodes, number of stamens, and seed morphology (Darlington, 1934; R. J. Hill, 1976; D. K. Brown and Kaul, 1981). Several species have edible seeds, which can be parched and ground into a flour, and a few species are cultivated for their showy flowers.