Geraea is a small genus of flowering plants in the family Asteraceae (the daisy family), order Asterales, native to the desert regions of the southwestern United States and northwestern Mexico. It contains only two accepted species and is commonly known as the desert sunflower.
Plants in this genus are annuals or perennials reaching 10–100 cm in height. Stems are erect and branched with ascending branches. The leaves are basal and cauline, arranged alternately, and may be sessile or petiolate; leaf blades are 3-nerved, varying in shape from elliptic to lanceolate, oblanceolate, oblong, or ovate, with entire or toothed margins and surfaces that are canescent (gray-hairy) or glandular-puberulent to stipitate-glandular.
Flower heads are radiate or occasionally discoid, borne singly or in open, paniculiform (panicle-like) arrays on peduncles that are usually longer than the involucres. The involucres are hemispheric, 7–15 mm in diameter, with 20–30 or more phyllaries in 2–3 or more series. Ray florets number 0 to 21 and are neuter with yellow corollas; disc florets number 60–200 or more and are bisexual, fertile, and also yellow. The fruits (cypselae) are black, strongly compressed, and narrowly wedge-shaped, with white long-ciliate margins and hairy faces. The pappus consists of 2 awns or subulate scales. The base chromosome number is x = 18.
The two species differ primarily in their glandularity and range: Geraea canescens (hairy desert sunflower) is the widespread species found across California, Arizona, Nevada, and Utah, while Geraea viscida (sticky desert sunflower) is restricted to the southern California counties of San Diego and Imperial, and adjacent Baja California.
Etymology
The name Geraea is derived from Greek geraios (γεραιός), meaning "old" or "venerable," likely alluding to the white-hairy (canescent) appearance of the plants. The common name "desert sunflower" reflects the genus's sunflower-like yellow ray florets and its arid desert habitat.
Distribution
Geraea is native to the Mojave Desert, Sonoran Desert, and adjacent arid regions of the southwestern United States and northwestern Mexico. Geraea canescens ranges across California, Arizona, Nevada, and Utah, while Geraea viscida is confined to San Diego and Imperial Counties of California and Baja California.
Ecology
Plants in the genus grow in desert scrub, sandy washes, and gravelly flats typical of the Mojave and Sonoran Deserts. The genus includes annual forms that can bloom prolifically following winter rains, contributing to desert wildflower displays. Glandular-puberulent surfaces in Geraea viscida distinguish it ecologically and morphologically from the canescent Geraea canescens.
