Mentzelia nuda (Pursh) Torr. & A. Gray
Family - Loasaceae
Stems - To 1 m, ascending to erect, stiff and brittle, often whitish in color, roughened with barbed hairs.
Stem and leaves.
Old stem and new growth.
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.
Flower and buds.
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.
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. As is common within the genus Mentzelia, various parts of the plant bear stiff trichomes of a unique
morphology which has been termed "pagodaform," each hair being ringed with minute whorls of barbs. This complex pattern of barbs gives
a peculiar feel to the epidermis, and also causes plant parts to stick tenaciously to clothing. Leaves will sometimes cling so tightly as
to survive laundering, and will also break apart into fragments before releasing their hold on the fabric. Another trait common to this genus
is odd flowering times, which in M. nuda is reported to be from late afternoon to sunset.
This species is easily distinguished from the other two Missouri species of Mentzelia by virtue of its large white
flowers. It grows on barren substrate, such as mine tailings, which supports little else.
This species is easily distinguished from the other two Missouri species of Mentzelia by virtue of its large white flowers. It 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).