(Verbena hastata)
Verbena hastata, the American vervain, blue vervain or swamp verbena, is a flowering plant in the vervain family Verbenaceae. It is a perennial herbaceous plant with opposite, simple leaves which have double-serrate margins, borne on stiffly erect, branching square stems. The purple flowers appear in summer. This is a common plant that occurs across North America. It is hardy and drought resistant. The Latin specific epithet hastata means "spear-shaped". This species is a member of the diploid North American vervains which have 14 chromosomes altogether. Hybridization seems to have played some role in its evolution, presumably between some member of a group including the white vervain (V. urticifolia), V. lasiostachys or V. menthifolia, and V. orcuttiana or a related species. In the recent evolutionary past, there has been an incident of chloroplast transfer of one of the latter or the swamp verbena to the mock vervain Glandularia bipinnatifida which is a close relative of the genus Verbena. It is unknown by what mechanism this happened, but it is suspected that hybridization is not responsible. It is a larval host to the common buckeye butterfly. Verbena, also known as vervain or verveine, is a genus in the family Verbenaceae. It contains about 150 species of annual and perennial herbaceous or semi-woody flowering plants. The majority of the species are native to the Americas and Asia; however, Verbena officinalis, the common vervain or common verbena, is the type species, and native to Europe. Verbena is an herbaceous flowering plant, belonging to the Verbenaceae family, and may be annual or perennial depending on the species. The leaves are usually opposite, simple, and in many species hairy, often densely so. The flowers are small, with five petals, and borne in dense spikes. Typically some shade of blue, they may also be white, pink, or purple, especially in cultivars. The genus can be divided into a diploid North American and a polyploid South American lineage, both with a base chromosome number of seven. The European species is derived from the North American lineage. It seems that verbena as well as the related mock vervains (Glandularia) evolved from the assemblage provisionally treated under the genus name Junellia; both other genera were usually included in the Verbenaceae until the 1990s.