Mentzelia oligosperma Nutt. ex Sims



CC = 6
CW = 5
MOC = 18

© SRTurner

Family - Loasaceae

Habit - Perennial forb with thick, woody roots.

Stem - To 80 cm, branched and spreading, brittle, the surface flaking when dry, roughened and densely pubescent with barbed hairs, whitish or gray.

Mentzelia_oligosperma_stem2.jpg Stem and pagodaform hairs.

© SRTurner

Mentzelia_oligosperma_stem.jpg Stem and leaves.

© SRTurner

Leaves - Alternate, simple, short-petiolate. Blades 1-7 cm long, 0.5-3.5 cm wide, lanceolate to rhombic, bluntly to sharply pointed at the tip, the margins coarsely and irregularly toothed and often also few-lobed, densely pubescent with barbed hairs.

Mentzelia_oligosperma_leaf1.jpg Leaf adaxial.

Blade is oriented perpendicular to ground, demonstrating adherent character.

© SRTurner

Mentzelia_oligosperma_leaf.jpg Leaf abaxial.

© SRTurner

Mentzelia_oligosperma_leaf2.jpg Pagodaform hairs at leaf base. See below also.

© SRTurner

Inflorescence - Teminal clusters of a few flowers, or solitary. Flowers subtended by 3-5 leaflike, irregularly toothed or narrowly lobed bracts.

Mentzelia_oligosperma_inflorescence.jpg Inflorescence.

© SRTurner

Flowers - Hypanthium 4-6 mm long, densely pubescent with barbed hairs. Sepals 5, 5-9 mm long, narrowly lanceolate, fused at the very base, shed as a unit before fruiting. Petals 5, 8-12 mm long, 5-6 mm wide, oblong-obovate, orange. Stamens usually about 25. Staminodes absent.

Mentzelia_oligosperma_flower2.jpg Flower.

© SRTurner

Mentzelia_oligosperma_hypanthium.jpg Hypanthium and sepals.

© SRTurner

Mentzelia_oligosperma_flower.jpg Corolla.

© SRTurner

Fruit - Capsule 7-14 mm long, cylindrical to clavate, densely pubescent with barbed hairs. Seeds 1-3 per fruit, 3-5 mm long, 1-2 mm wide, pendulous, not winged, narrowly oblong-elliptic in outline, 3-angled, the surface finely grooved with numerous wavy lines, brown.

Mentzelia_oligosperma_fruit.jpg Fruit.

© SRTurner

Flowering - June - August.

Habitat - Ledges, bluff tops, upland forest openings, glades, railroads. Usually on calcareous substrate.

Origin - Native to the U.S.

Lookalikes - None.

Mentzelia_oligosperma_hairs.jpg Pagodaform hairs on leaf margin.

Focus-stacked photomicrograph courtesy of Rick Gray.

© RGray

Other info. - This species is Missouri's only native Mentzelia. The common names refer to the tendency of the plant parts to adhere tenaciously to fur, feathers, or clothing. A field botanist whom I know has had Mentzelia leaves persist on his trousers through airline travel and subsequent laundering. This tenacity is caused by the presence of complex hairs bearing whorls of retrorse barbs (see image above). These "pagodaform" hairs are a distinguishing feature of the Mentzelia genus.

Mentzelia oligosperma rewards early-rising observers with richly colored flowers, which are fully open only in the morning. The species epithet "oligosperma" refers to the relatively small number of seeds per capsule.

Photographs taken at Castlewood State Park, St. Louis County, MO, 8-9-2010, Danville Conservation Area, Montgomery County, MO, 8-23-2016, and Klondike County Park, St. Charles County, MO, 6-11-2022 (SRTurner). Focus stacked image of hairs by Rick Gray, 7-7-2020.