Vervain family (Verbenaceae)
Description: This herbaceous perennial wildflower is ¾-2½' tall and ascending to erect. It often branches near the base, while above it is unbranched or sparingly branched. The stems are glabrous or short-pubescent; pairs of opposite leaves occur at intervals along these stems. The narrow leaves are 1¼–4" long and less than ½" across; they are narrowly oblanceolate or narrowly elliptic in shape and smooth to coarsely toothed along their margins. There are more teeth toward the tips of the leaves than at their bases. The leaves taper gradually into petiole-like bases. Their upper surfaces are pale to medium green and glabrous or sparsely short-pubescent.
The stems terminate into spike-like racemes of flowers about 4-12" long; there is only one raceme per stem. Only a few flowers bloom at the same time, beginning at the bottom and ending at the top of each raceme. Individual flowers are up to ¼" across, consisting of a lavender to nearly white corolla with 5 spreading lobes, a short tubular calyx with 5 teeth, 4 inserted stamens, and a pistil with a single style. At the base of each flower, there is a lanceolate leafy bract that is about the same length or a little shorter than the calyx. The blooming period occurs during the summer for about 2 months. Afterwards, the flowers are replaced by nutlets (4 per flower). These nutlets are oblongloid, somewhat flattened, and about 1/8" long.
Cultivation: The preference consists of full sun, dry-mesic to dry conditions, and gravelly alkaline soil. Sandy soil is also acceptable if it isn't too acidic.
Range & Habitat: The native Narrow-Leaved Vervain is occasional throughout Illinois. Habitats include dry gravel prairies and dolomite prairies, hill prairies, limestone glades, gravelly areas along railroads and roadsides, abandoned fields, and barren waste areas. This species prefers sunny areas with scant vegetation.
Faunal Associations: The flowers attract bees, skippers, and probably butterflies. Robertson (1929) observed little carpenter bees (Ceratina sp.), cuckoo bees (Epeolus sp., Coelioxys sp.), leaf-cutting bees (Megachile sp.), green metallic bees (Augochlorella sp.), and the Silver-Spotted Skipper (Epargyreus clarus) visiting the flowers for nectar. Two oligophagous insects, Crambodes talidiformis (Verbena Moth) and Macrosiphum verbenae (Verbena Aphid), feed on Verbena spp. The seeds are a minor food source for the Lark Bunting (in the Great Plains) and several native sparrows that prefer open habitat.
Photographic Location: A prairie in Fayette County, Illinois. The photograph of the blooming plant was taken by Keith & Patty Horn (Copyright © 2009).
Comments: Narrow-Leaved Vervain can be distinguished from other Verbena spp. by its narrow leaves (less than ½" across) and long slender spikes of flowers (actually, spike-like racemes because the flowers have short pedicels). Its flowers are smaller in size than those of Verbena stricta (Hoary Vervain), but larger in size than other Verbena spp. within the state. This comparison excludes Rose Vervain, which has been reassigned to a different genus (Glandularia). Narrow-Leaved Vervain can form hybrids with other species in its genus. Two of these hybrids have been found within the state: Verbena × blanchardii (with Verbena hastata) and Verbena × moechina (with Verbena stricta).