Yellow-flower desert evening-primrose
The Mojave, Sonoran and Chihuahuan Deserts, and adjacent regions
Sandy flats, hillsides, dunes, washes; up to 4,500 feet
Narrowly lanceolate or oblanceolate, with pinnately lobed edges; up to 11 inches long
Petals of oenothera primiveris are light yellow, slightly darker yellow or greenish at the base, and become pale pink to orange as they wither. Petal length varies between 1 and 1.5 inches (ssp bufonis, centered on the Mojave Desert) or between 0.25 and 1 inches (ssp primiveris, the Mojave Desert, and extending east into Texas). Petals are heart-shaped, with a lengthwise groove down the middle extending to a deep notch at the tip, and generally not overlapping when fully open. Sepals are green, up to an inch or more in length, and recurved.
Plants usually have no stems; leaves form as a basal rosette, and the flower stalks also emerge at ground level. The green or gray-green leaves are usually pinnately divided almost to the midvein, into irregularly shaped lobes, often alternating between large and small. Leaves may have a much longer terminal lobe. Leaves and flower stalks have a dense covering of short hairs. Some of the hairs have reddish bases, while those on the sepals may be glandular.