Prairie verbena [Glandularia bipinnatifida (Nutt.) Nutt.] is a common wildflower native from the Mississippi River west to Arizona and from southern Mexico north to South Dakota (Umber, 1979). Correll and Johnston (1970) reported Verbena bipinnatifida Nutt., the previous scientific classification for prairie verbena, often covers large acreages in dry plains, prairies, pastures, and disturbed roadsides. These large populations are associated frequently with gypsum, limestone, or calcareous soils (Umber, 1979).
Prairie verbena has a variable growth habit. Plants of a similar age from the same population may be either prostrate or erect (Umber, 1979). Habit variability may also be related to growing conditions and season. In early spring during short days, the internodes are reduced and the plants are more prostrate. As day length increases, internode length increases and the plants attain a more upright habit. Prairie verbena has densely branched stems covered with stiff white hairs (Correll and Johnston, 1970), leaves that are deeply incised, and several growth forms or ecotypes resulting in some attaining specific or varietal status.
Prairie verbena blooms primarily from March through June and less freely through October. In moist situations in the South, flowering continues unabated throughout the growing season, enhancing the use of this native for edge work in the garden (Irwin and Wills, 1961). The colors can range from pink to lavender or a rosy purple within G. bipinnatifida. Diggs et al. (1999) described the arrangement of these flowers as a simple dichasium of spikes that increases in complexity with an increase in individual plant size. The term Glandularia was derived from the glandular appearance of the stigmatic area of the flowers. The specific epithet bipinnatifida was a result of the leaf appearing bipinnately compound.
Prairie verbena exhibits multiple types of seed dormancy; thus, the seed requires a minimum of 26 weeks of cool, dry storage for the initiation of germination (Vyas and Agarwal, 1970). Germination may be enhanced with supplemental light treatments used after imbibition (Vyas and Garg, 1973).
Diggs, G.M. , Lipscomb, B.L. & O'Kennon, R.J. 1999 Shinners & Mahler's illustrated flora of north central Texas Botanical Research Institute of Texas, Ft Worth, Texas
Vyas, L.N. & Garg, R.K. 1973 A reversible photoreaction controlling germination of Verbena bipinnatifida Nutt. Seeds Biochem Physiol Pflanzen. 164 636 663