Mentzelia nuda (Pursh) Torr. & A. Gray
CC = *
CW = 5
MOC = 1
Family - Loasaceae
Habit - Biennial or perennial forb with a thickened taproot.
Stems - To 1 m, ascending to erect, stiff and brittle, often whitish in color, roughened with barbed hairs.
Leaves - Alternate, short-petiolate, simple, pinnately lobed or broadly toothed, to 10 cm long, oblanceolate or narrowly elliptic, with abundant barbed trichomes on both surfaces.
Inflorescence - Solitary terminal flowers or small racemose or paniculate clusters. Flowers subtended by 3-5 leaflike bracts.
Flowers - Sepals 5, to 25 mm long. Petals apparently 10 (including 5 petaloid staminodes), to 5 cm long, oblanceolate, creamy white. Stamens numerous, the outer five flattened and modified into petalloid staminodes indistinguishable from petals. Filaments unequal, shorter toward flower center, fused together basally and to the petal bases. Hypanthium to 18 mm long. 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, cylindrical or barrel-shaped, to 3 cm long, densely pubescent with minute barbed hairs, dehiscent by an apical valve.
Seeds - Numerous, flattened and broadly winged, 2.5-3.5 mm in diameter, the surface minutely pebbled, tan.
Flowering - July - September.
Habitat - Open, sandy, disturbed areas.
Origin - Native to the U.S. Great Plains region.
Lookalikes - None.
Other info. - This striking and unmistakable species is rare in Missouri, having been found in only a single location so far. It was apparently introduced there, as the population is disjunct from its natural range in more western areas of the country. This species is easily distinguished from the other two Missouri species of Mentzelia by virtue of its large white flowers. The plant grows on barren substrate, such as mine tailings, which supports little else.
Photographs taken at St. Joe State Park, St. Francois County, MO, 8-8-2009, 8-14-2009, and 9-5-2018 (SRTurner).