Found across the Southwest, these showy perennials share the same common name as some of their close relatives (and look-alikes) in the genus Oenothera. Bloom over a long season, from spring into late fall, bearing bright yellow, four- petaled flowers that open at sunset and remain open for most of the next day. Plants go dormant in winter and may be sheared just before spring growth begins. They spread by rhizomes and can take over a garden bed if unrestrained by a physical barrier, such as metal edging sunk 6 in. deep into the ground. Good for summer color in rock gardens or on rocky slopes; make nice filler plants in mixed borders. Like lots of heat and excellent drainage.
C. berlandieri (Oenothera berlandieri). SQUARE BUD PRIMROSE. Native to Texas, northern Mexico, and the Gulf states. This tough garden perennial grows to 1 ft. tall and 3 ft. wide. The fine-textured foliage gives background to these 1-2 in. flowers in spring and early summer. Great for trailing over a low wall where it enjoys good drainage.
C. drummondianus. To 112 ft. high, 2 ft. wide, with narrow, tooth-edged, somewhat drooping leaves and inch-wide flowers. This species blooms for a longer period than C. hartwegii in spring, but it does not rebloom as well in fall.
C. hartwegii. To 1 ft. high, 2 ft. across, with inch-wide flowers; those of 'Sierra Sundrop' are larger. C. h. lavandulifolius has narrow, gray leaves. Excellent in hot, dry locations and when mixed with desert perennials.
C. serrulatus. US, MS, LS; USDA 6-8. Prairie wildflower found from Saskatchewan to Texas. To 112 ft. high and wide, with 34-in. flowers.
C. 'Southern Belle'. LS, MS, CS, TS; USDA 8-11. Complex hybrid to 812 in. tall, 18 in. wide. Long-blooming and well-behaved, producing no seeds.