Description: This short-lived perennial plant is up to 3½' tall, branching occasionally. The stems are heavily covered with long white hairs. The opposite leaves are up to 4" long and 2½" across. They are ovate, oblong, or obovate (approximately spoon-shaped), and coarsely serrated along the margins. The whitish green leaves are covered with fine white hairs (on both sides), and are sessile or have short petioles. In addition to the pinnate venation, there is a reticulated network of smaller veins. Near the apex of the plant, are one or more hairy spikes, from 1-6" long, which are densely crowded with pink or lavender flowers. The flowering spikes bloom from the bottom up. Each flower is a little larger than ¼" across, with 5 lobes that flare outward from a short corolla with a narrow opening. There is no floral scent. The blooming period occurs from mid- to late summer, and lasts about 1½ months. Four brown nutlets are produced per flower. The root system consists of a central taproot, which may tiller from the base (send up multiple stems). Reproduction is by seeds, which germinate readily.
Cultivation: The preference is full sun, and average to dry conditions. Generally, Hoary Vervain flourishes in poor soil consisting of clay, sand, or gravel. In rich loamy soil, it will grow well, but has difficulty competing with other plants. Drought resistance is good, although some of the lower leaves may shrivel and fall off the plant.
Range & Habitat: Hoary Vervain occurs in almost every county of Illinois and is fairly common, although possibly less so than in the past. It can be found in dry areas of black soil prairies, gravel prairies, hill prairies, barrens with stunted shrubby vegetation, limestone glades, overgrazed pastures, abandoned fields, the grassy shoulders of highway overpasses, and areas along railroads. It favors grassy areas with a history of disturbance, particularly from grazing, and dry uplands with poor soil and sparse vegetative cover.
Faunal Associations: Many kinds of insects are attracted to the flowers, including long-tongued bees, Green Metallic bees, Thread-waisted wasps, Bee flies, Thick-headed flies, butterflies, and skippers. Among the long-tongued bees, are such visitors as honeybees, bumblebees, Little Carpenter bees, Cuckoo bees, Miner bees, and large Leaf-cutting bees. A specialist visitor of the flowers is Calliopsis verbenae (Verbena Bee). The caterpillars of the moths Catabena lineolata (Fine-Lined Sallow) and Crambodes talidiformis (Verbena Moth) feed on the foliage. The seeds are eaten by various songbirds to a limited extent, including the Cardinal (winter), Slate-Colored Junco (winter), Field Sparrow, and possibly others. It is possible that these birds help to distribute the seeds, which may be only partially digested, like many common weeds. Mammalian herbivores rarely eat this plant because the foliage is quite bitter. It is considered an 'increaser' in overgrazed pastures.
Comments: This plant is somewhat weedy-looking, but less so than many other vervains. Because of the distinctive spikes of flowers and hairy stems and leaves, Hoary Vervain is easy to identify.