This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol2", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Erect herbs, mostly annuals, with alternate entire lobed 01 pinnatifid leaves, and terminal solitary or cymose flowers. Calyx-tube cylindric, linear or club-shaped, its limb generally 5-lobed. Petals 5, spreading, convolute in the bud, deciduous Stamens 20-100. Ovary I-celled; styles 3, more or less united; stigmas small, obtuse. Capsule dehiscent at the summit, few-many-seeded. Seeds mostly prismatic, not separated by horizontal lamellae, roughened or striate. [Named in honor of C Mentzel, a German botanist, died 1701.]
About 35 species, natives of America. Besides the following, some 20 others occur in the western parts of North America. Type species: Mentzelia aspera L.
Leaves sessile; stem little rough; calyx-lobes 2" long.
Leaves, at least the lower, petioled; stem very rough; calyx-lobes 3" long.
Mentzelia oligosperma Nutt. in Bot. Mag. pl. 1760.
1815. Mentzelia aurea Nutt. Gen. 1: 300. 1818
Rough and viscid-pubescent, 1°-3° high. Leaves ovate or oval, coarsely dentate or sinuate, acute or obtusish at the apex, 1'-3' long, the upper rounded or truncate at the base and sessile, the lower narrowed at the base and usually petioled; flowers yellow, 5"-10" broad, axillary or somewhat cymose, opening in sunshine; petals 5, oblong-cuneate, acute, about twice as long as the linear-lanceolate calyx-lobes; filaments 20-30, all filiform; capsule linear, 6"-8" long, few-seeded; calyx-lobes about 3" long; seeds oblong, wingless.
Mentzelia albicaulis Dougl.; T. & G Fl. N. A. 1: 534.
1840. Bartonia albicaulis Dougl.; Hook. Fl. Bor. Am. 1:
Stem nearly white, erect or ascending, slender, branched, shining, nearly smooth, or roughish above, 6'-2° high. Leaves sessile, mostly lanceolate in outline, sinuate-pinnatifid, sinuate-lobed, or the upper and lower sometimes entire, rough with short, stiff hairs, 1'-3' long; flowers yellow, few together at the ends of the branches, or also axillary, 6"-10" broad, short-pedicelled or sessile; calyx-lobes linear-lanceolate, about 2" long; filaments separate; capsule linear, 1' long or less, many-seeded; seeds angled, tuberculate, wingless.
Western Nebraska to British Columbia, California and New Mexico. May-July.