FAMILY: Onagraceae — Evening Primrose family
OTHER COMMON NAMES: Fragrant evening primrose, Stemless evening primrose
ETYMOLOGY: The Greek roots of the name of the genus Oenothera are disputed, but in Latin, the word refers to a soporific (sleep-inducing) plant.
The species epithet caespitosa refers to the plant's growth habit—a dense cluster, or tuft, or leaves.
GEOGRAPHIC RANGE: Native to much of western and central North America and south into Chihuahua and Baja California
HABITAT: Rocky slopes, 4,000–7,500'
BLOOMING SEASON: April to September, with the heaviest bloom occurring in spring
DESCRIPTION: Perennial plant that grows to 12" high from a woody taproot. The plant grows in clumps that can spread to 24" across.
Gray green leaves have a conspicuous white to pinkish midrib and are sometimes tinged with red. Leaves have toothed margins and are covered with fine hairs. They grow from a basal rosette to 7" long by 1" wide.
Three to four-inch wide white flowers grow from the center of the rosette of leaves and are quite large in relation to the leaves. The corolla consists of four heart-shaped petals, each 2" long and 3/4" wide, surrounded by four pinkish sepals that curve upwards. At the center of the flower are 8 yellow stamens and a prominent 4-lobed stigma. Flowers are held above the foliage not by stems but by long, thin floral tubes. Fruit is a cylindrical capsule, 1-2" long.
Flowers bloom for one night only, opening in the late afternoon. As morning temperatures increase, the flowers wilt and turn pink.
Plant-Insect Associations: Tufted evening primrose is a moth-pollinated species with characteristics necessary for attracting moths: light color, fragrance, a narrow floral tube, and a slender or absent stem (as moths hover when feeding and instead of landing on the plant, they do not need a sturdy stem to support their weight).
Many plants transfer pollen grains to their insect pollinators's bodies as they brush up against the flower's anthers. As the primrose pollinators' bodies do not actually enter the flower, the pollen grains, attached to sticky strings, adhere instead to the moths' tongues while they are feeding.