Evening Primrose family (Onagraceae)
Description: A native biennial plant that is 4-6' when mature, branching frequently in the upper half to produce long flowering stems. The angular stems are covered with white hairs that are soft and long. These hairs are more or less straight, and spread away from the stem. The light green leaves are about 5" long and 1½" across when full-sized. They usually alternate along the stems, but sometimes occur in whorls where a new stem emerges from an older stem. The leaves have very short or no petioles, are lanceolate or ovate in shape, and have margins that are smooth or slightly dentate, depending on the local ecotype. The leaves often turn red during late summer or fall.
The numerous small flowers are usually light pink, but are sometimes white or reddish pink, depending on their maturity. They have a slight fragrance. There are 4 petals loosely arranged toward the top of each flower, while 8 yellow stamens hang loosely downward. These flowers occur on long spikes or panicles that project upward and outward in different directions. The blooming period is during late summer for about 1½ months. The root system is fibrous, while reproduction is by seed. The entire plant is flimsily constructed, and sways with each passing breeze, thereby distributing the seeds.
Cultivation: The preference is full sun and moist to dry conditions. Either clay or gravelly soil are tolerated. This plant forms a rosette during the first year, and grows rapidly upward during the second year. Foliar disease is not normally bothersome, but insect attacks are common, particularly from Japanese Beetles.
Range & Habitat: Biennial Gaura occurs in most counties of Illinois, and is locally common (see Distribution Map). It colonizes disturbed areas in various habitats, including mesic to dry prairies, clearings in upland woodlands, limestone glades, abandoned fields, miscellaneous waste areas, and exposed gravelly banks along rivers, roadsides, and railroads.
Faunal Associations: Long-tongued bees are the primary pollinators, especially bumblebees. They collect pollen or suck nectar. Moths may visit the flowers for nectar during the day or night, such as Heliothis zea (Northern Corn Earworm Moth). Some Flower moths also visit the flowers to lay their eggs specifically, Schinia florida (Primrose Moth) and Schinia gaurae (Gaura Moth). Their larvae feed on the flowers and seed capsules. The former moth often hides underneath the Gaura flowers during the day, and is well-camoflauged because of its pink color. Various mammalian herbivores browse on this plant, such as deer and livestock.
Photographic Location: The upper photograph was taken of a flowering plant growing along a railroad in Champaign, Illinois, while the lower photograph was taken of a plant at Meadowbrook Park in Urbana, Illinois.
Comments: This native plant is often ignored because it is a rather widespread biennial with an untidy appearance. However, it contributes some color and fragrance to the prairie or wildflower garden during the hot and dreary month of August. Biennial Gaura closely resembles Gaura longiflora (Large-Flowered Gaura), except the latter species has shorter white hairs that tend to lie flat against the stems, instead of spreading outward.