Leaves of the Creosotebush are covered with a “varnish” which often glistens in the sunlight, and helps reduce evaporative moisture loss, thereby enabling the plant to resist the desiccating effect of hot, dry winds. YELLOW [Illustration: Wislizenia refracta] Common name: JACKASS-CLOVER Arizona desert: (_Wislizenia refracta_). Yellow. May-September. Caper family. Size: Up to 4 feet in height. Conspicuous in late summer along roadsides and dry streambeds, the large number of yellow flowers and the widespread presence of these much branched, annual plants justify the inclusion of Jackass-clover in this booklet as one of the common flowers of the desert. The plant ranges across the Southwest from western Texas to southern California at elevations between 1,000 and 6,500 feet. The flowers themselves are small, although the flower heads are quite conspicuous. Since the leaves somewhat resemble the tri-foliate leaves of Clover, the plant is commonly called Jackass-clover. It is usually found in sandy locations. YELLOW [Illustration: Oenothera primiveris O. brevipes O. deltoides O. cardiophylla] Common names: EVENING-PRIMROSE, SUNDROP Arizona and California deserts: (_Oenothera brevipes_). Yellow. March-May. Texas-New Mexico deserts: (_Oenothera primiveris_). Yellow. March-May. Evening-primrose family. Size: Usually low, but some up to 5 feet. Among the commonest but most beautiful and delicate of the flowering plants of the desert are the Evening-primroses. Flowers are usually large, with the four petals either white or yellow, turning to red or pink with age. Many species are low-growing herbs with large, delicate petals; while others may be shrub-like, sometimes attaining a height of 5 feet. As the name implies, the flowers open in the evening and wilt soon after sunrise. In the low, warmer sections of the desert, plants in blossom may be found as early as February. YELLOW [Illustration: Berberis trifoliata Berberis haematocarpa] Common names: ALGERITA, BARBERRY, HOLLYGRAPE Arizona desert: (_Berberis haematocarpa_). Yellow. February-April. California desert: (_Berberis fremonti_). Yellow. May-July. Texas desert. (_Berberis trifoliolata_). Yellow. Spring. Barberry family. Size: Shrubs, 3 to 8 feet.