Basis for Listing

Verbena simplex is primarily found in the eastern continental U.S. and eastern Canada. It is rare at the edges of its range, including in New England, North and South Carolina, Nebraska, Wisconsin, and Minnesota. The species was first collected in Minnesota in 1891 and it has only been observed four times since then. Furthermore, only one of the observations has been made in the last 20 years (1991). While it is possible that a few populations may have been overlooked, it is clear that V. simplex is quite rare in Minnesota. It was listed as a special concern species in 1984.

  Description

Verbena simplex is a slender plant that may branch or have single stems. It has spikes of small lavender flowers and square stems. The stems and leaves have minute hairs that are short, sharp, and stiff, and they lie against the leaf or stem surfaces. In Minnesota, the species ranges in height from 30-60 cm (11.8-24.0 in.). One to several stems emerge from the base of the plant and each stem may be simple or branched above. The leaf shape may be linear or narrowly oblong and tapering to a narrow base. The leaves attach almost directly to the stem, with no leaf stalk. Leaf dimensions are typically 3-8 cm (1.2-3.1 in.) long and up to 15 mm (0.59 in.) wide. Leaves are serrate, at least toward their tips.

The flower spikes are slender and erect and can be quite long, ranging from 3-24 cm (1.2-9.4 in.). They are usually borne singly at the end of a stem or branch, and the flowers are densely clustered in the spike. The petals are only slightly longer than the calyx; flowers are some shade of blue or purple (or rarely white), and about 7 mm (0.28 in.) across (Tans and Iltis 1979; Great Plains Flora Association 1986).

There are 4 common species of Verbena in Minnesota. All have wider leaves (over 1 cm (0.4 in.) wide) than V. simplex, and 2 of them have multiply branched inflorescences, whereas V. simplex has only 1-3 inflorescence branches.

  Habitat

Verbena simplex seems to prefer open, dry conditions on circumneutral soils (Elliman 2002). The few Minnesota habitats where V. simplex has been observed include thin soil over quartzite bedrock outcrops, a roadside prairie, and a dry hillside adjacent to a road. Throughout its range, V. simplex is found in early successional fields, edges of woods, and rock outcrops (Elliman 2002). In Wisconsin, it has been found in sandy open fields, basalt bedrock glades, and along gravel roads (Wisconsin Botanical Information System 2010).

  Biology / Life History

Verbena simplex is insect pollinated (Moldenke 1958 as cited in Elliman 2002), although specific pollinators are not known. Other species of Verbena are known to be pollinated by bees, wasps, flies, and butterflies (Perkins et al. 1975 as cited in Elliman 2002). Verbena simplex can reproduce without being cross-pollinated with pollen from another individual (Barber 1982). Hybrids within the Verbena genus are common and V. stricta (hoary vervain) in particular can hybridize with each of the other species (Barber 1982).

The best time to search for V. simplex is when it is flowering or fruiting, from mid-June through September.

  Conservation / Management

Since there are very few records of this species in Minnesota, it is hard to draw conclusions about appropriate conservation and management practices. We do know that it occurs in open, upland habitats, such as rock outcrops and prairie settings, and that fire is important in the maintenance of these dry, open habitats (Minnesota DNR 2005). It is possible that V. simplex needs some form of disturbance to persist (Elliman 2002), and prescribed fire would provide this by reducing shading from woody species and creating patches of bare ground where seeds could easily germinate.

  Conservation Efforts in Minnesota

The most recently observed Minnesota population occurs on rock outcrops within Blue Mounds State Park. However, no known conservation efforts have been undertaken specifically on behalf of V. simplex at this or other sites.