Monoptilon, commonly called desertstar, is a small genus of two species of annual wildflowers in the family Asteraceae (the daisy family), placed in the tribe Astereae. The genus is endemic to the deserts of North America, with species occurring across California, Nevada, Arizona, Utah, Baja California, and Sonora.
Plants are tiny, rarely exceeding 5 cm in height, with a hispido-hirsute indumentum of long white hairs and minute glands. The stems are prostrate to decumbent, radiating outward from a central taproot in a mat-like fashion, and may be simple or branched. Leaves are basal and cauline, alternate, and petiolate, with oblong to oblanceolate-spatulate blades bearing entire margins. Despite their diminutive stature, the solitary flower heads are conspicuous: each campanulate involucre (4–6 mm tall, 6–7 mm wide) bears 10–14 purple-tipped, hirsute phyllaries and is typically nestled among and subtended by the uppermost leaves. The 12–21 ray florets produce white to rose- or purple-tinged corollas that characteristically coil strongly after anthesis. The 28–40 disc florets are yellow with prominent orange veins. Fruits (cypselae) are brownish, obovoid, compressed, and 2-ribbed; the pappus is persistent and distinctive, consisting of a short-toothed basal cup plus either a single apically plumose bristle or a set of 8–15 barbellate bristles with outer short laciniate paleae. The chromosome number is x = 8 (2n = 16) for both species.
Phylogenetically, Nesom (1994) placed Monoptilon as sister to Chaetopappa within Astereae. The two recognized species are M. bellidiforme (daisy desertstar) and M. bellioides (Mojave desertstar).
Etymology
The name Monoptilon derives from the Greek mono- (one) and ptilon (feather or wing), an allusion to the single apically plumose (feather-like) bristle that forms a distinctive part of the pappus in at least one species of the genus.
Distribution
Monoptilon is native to the arid regions of the southwestern United States and adjacent Mexico. M. bellidiforme (daisy desertstar) occurs in California, Nevada, Arizona, and Utah; M. bellioides (Mojave desertstar) ranges through California, Nevada, and Arizona and extends south into Baja California and Sonora, Mexico.
Ecology
Both species are spring-blooming desert annuals that exploit brief windows of winter–spring rainfall in Mojave and Sonoran Desert habitats. Their prostrate, mat-forming growth habit and taproot suit open sandy or gravelly desert flats and washes where competition is low.
