Southwest Colorado Wildflowers, Acrolasia and Nuttallia

The Mentzelia genus is, in the words of Intermountain Flora, "a difficult group taxonomically. [There is] a close relationship.. among many of the taxa and [a] confusing array of intermediates.... The taxonomy of [most of the Mentzelias] at the level of species is beset with difficulties, and there is presently no generally accepted interpretation." Stanley Welsh, author of A Utah Flora, says, "Plants in this genus are sometimes difficult to place with certainty.... The notorious variability of plant size, leaf size, shape, and lobbing, flower size, and size and shape of capsules contributes to the difficulty. Many of the features grade hopelessly into each other...."

So don't feel so bad about not being certain of the identification of some species. The first species below, Acrolasia albicaulis (Mentzelia albicaulis of most literature) is distinct enough to feel confident about. I have identified the next species as Nuttallia pterosperma (Mentzelia pterosperma of most literature) but it is possible these are Nuttallia multiflora or hybrids. Most botanists place both species below in the Mentzelia genus.

The hairs of this family are special and are described as follows by William Weber: "The sandpaper surface of the leaves of Loasaceae is caused by some of the strangest plant hairs known. These multicellular hairs are "pagodaeform," i.e., broad-based, shaped like a pagoda, each cell capped by a ring of stiff, curved hooks, which, unlike the corners of pagoda roofs, curve down, not up. There is hardly an article of clothing that will not carry away the leaves or fruits".

Synonym: Acrolasia albicaulis. Mentzelia albicaulis. (White-Stemmed Mentzelia)
Loasaceae (Loasa Family)

Desert, semi-desert. Openings. Spring.
McElmo Canyon, Canyons of the Ancients National Monument, April 2, 2005.

This very slender, daintier cousin of Nuttallia pterosperma (below) is often more numerous, but because of its size, more difficult to find. Its stem is quite light in color and its basal rosette of leaves and its flowers are small. Flowers appear at first to be pointed but after many hours they open slowly into distinctive, tubular flowers with lobed petals. Flower stems frequently nod. Plants grow to about a foot tall.

"Acrolasia" is from the Greek for "summit hairs" and refers, Weber theorizes, "to hairs at petal tips".

Synonym: Acrolasia albicaulis. Mentzelia albicaulis. (White-Stemmed Mentzelia)
Loasaceae (Loasa Family)

Desert, semi-desert. Openings. Spring.
McElmo Canyon, Canyons of the Ancients National Monument, April 25, 2009.

The first three photographs below show a young plant on a hot, south facing, steep, gravelly slope. The next photographs (and the one immediately above) show a plant one month later at the side of a road where it received good moisture. I have identified both plants as Nuttallia pterosperma, but it is possible that they are not the same species and it is possible that they are both a different species of the Nuttallia genus, most likely Nuttallia multiflora. These two species are very similar and various floral keys separate them on the basis of conflicting characteristics. As the discussion at the top of this page indicates, this genus is in need of considerable work and precise identification of species is often difficult.