Mentzelia albescens (Gillies ex Arn.) Benth. & Hook. f. ex Griseb.

Wavyleaf Blazing Star

© SRTurner

Family - Loasaceae

Habit - Biennial or perennial forb with a thick taproot.

Stem - Erect, to 60 cm, brittle, whitish in color, densely pubescent with barbed hairs.

	Stem and leaves.
© SRTurner

	Stem with complex hairs.
© SRTurner

Leaves - Alternate, simple, short-petiolate. Blades 3-15 cm long, 1.0-2.5 cm wide, linear to ovate-lanceolate, rounded to bluntly or sharply pointed at the tip, the margins coarsely and broadly toothed or lobed, densely pubescent with barbed hairs.

	Leaf abaxial.
© SRTurner

	Leaf margin with barbed hairs.
© SRTurner

Inflorescences - Terminal solitary flowers, or small terminal clusters. Flowers subtended by 1-3 narrow entire bracts.

Flowers - Actinomorphic, perfect. Hypanthium 10-20 mm long. Sepals 5, 3-6 mm long, linear, withered but persistent at fruiting. Petals apparently 10 (including 5 petaloid staminodes), 6-8 mm long, 1-2 mm wide, lanceolate to spatulate, narrowed to a sharply pointed tip, lemon yellow to pale yellow. Stamens to 30-40, the outer 5 modified into petaloid staminodes (indistinguishable from the petals). Carpels 3, fused. Ovary inferior, with 1 locule. Flowers closed during the day, opening at dusk.

	Flowers (daytime, 10:17 a.m.). The spreading yellow appendages are calyx lobes.
© SRTurner

	Flowers (dusk, 7:34 p.m.).
© SRTurner

	Corollas. These have five true petals alternating with five petalloid staminodes.
© SRTurner

Fruits - Cylindrical capsules 18-28 mm long, 6-7 mm in diameter, densely pubescent externally with barbed hairs. Seeds numerous, 2-3 mm in diameter, positioned horizontally, flattened, winged, the seed coat minutely pebbled, tan.

	Immature fruits.
© SRTurner

	Fruit, top view.
© SRTurner

	Mature fruits.
© SRTurner

Flowering - May - August.

Habitat - Mine tailings, railroads, sandy disturbed areas.

Origin - Native to south-central U.S. and southward.

Other info. - This is one of only three Missouri representatives of a fascinating genus. The species is uncommon in the state, thus far reported from only five counties. It is scarcely more common elsewhere in the U.S., being known from only a few additional counties in Oklahoma and Texas. It is distinguished from the other two Missouri members of the genus by having yellow flowers which appear to have 10 petals (five of these are actually petal-like staminodes). The flowers are normally closed during the daytime, opening at dusk. This suggests pollination by moths. The images above showing closed and open flowers were taken a few hours apart on the same day.

Perhaps the most notable characteristic of these plants is a dense covering of complex hairs. The hairs are barbed, with many having a morphology which has been termed "pagodaform," bearing minute whorls of retrorse barbs. This feature causes plant parts such as leaves to stick tenaciously to fur or clothing. One prominent Missouri botanist has spoken of leaves stuck to his trousers surviving both a plane flight and a subsequent laundering. Foliage adhering to clothing often must be removed in pieces, as the leaves break before they release their grip on the fabric. This tenacity can be a major nuisance in sheep ranching, as it renders the wool unusable.

Plants in this genus are much more common in western states. The number of species is large, and differentiation can be difficult. Several species are endemic to relatively small regions.

Photographs taken near Pacific, St. Louis County, MO, 8-11-2010 and 7-13-2012 (SRTurner).