3. Verbena L. (vervain)

Plants annual or perennial herbs (shrubs elsewhere). Stems 1 to several from the rootstock, strongly ascending to erect, in V. bracteata usually loosely ascending or creeping with ascending tips, not rooting at the nodes, weakly to more commonly strongly 4-angled, glabrous or more commonly hairy. Leaves sessile or with a partially to entirely winged petiole, variously unlobed to 3-lobed or pinnately deeply divided, the segments then variously shaped, the margins usually sharply toothed, sparsely to densely hairy. Inflorescences terminal on the branches, not associated with slender, elongate stalks, short to elongate, dense to open spikes, sometimes appearing as more or less globose (not flat-topped) heads, sometimes grouped into panicles. Calyces tubular to narrowly bell-shaped, 1.5–5.0 mm long, 5-lobed, the lobes somewhat unequal in length, narrowly to broadly triangular, erect at flowering and fruiting or sometimes becoming slightly incurved as the fruits mature, sparsely to densely hairy on the outer surface and usually also along the margins. Corollas 2–10 mm long, funnelform to trumpet-shaped (sometimes narrowly so), slightly zygomorphic, 5-lobed, lavender to purple, purplish blue, or white, rarely pink, often fading to dark blue, the limb 2–9 mm in diameter, the lobes sometimes shallowly and broadly notched at the tip. Stamens inserted at 2 levels below the tip of the corolla tube, lacking a glandular appendage between the anther sacs. Ovary 4-locular, appearing 4-lobed, slightly concave at the tip. Style 2–3 mm long, the sterile lobe not extending beyond the fertile lobe, flattened and triangular. Fruits consisting of (2–)4 nutlets, these more or less oblong in outline, 3-angled in cross-section, mostly rounded to truncate at the tip, not concave at the base, the surface variously wrinkled, lined, and/or with a network of blunt ridges, sometimes also with small papillae, especially along the inner surface, grayish brown to dark brown or less commonly black. About 150 species, nearly worldwide, but most diverse in warm-temperate to tropical regions of the New World.

Mühlenbach (1979) reported a nonnative occurrence of the Texas vervain, V. halei Small (V. officinalis L. ssp. halei (Small) S.C. Barber), in Missouri, based on plants that he encountered during his botanical inventories of the St. Louis railyards. However, no voucher specimens could be located during the present study to support this claim. For the present, the species is thus excluded from the Missouri flora. Verbena halei differs from the species in the genus documented to grow in Missouri in having at least the lower leaves one or two times pinnately divided nearly to the midvein (Pl. 573 i, j). It is widespread in the southern United States and adjacent Mexico.

Several species of vervains are cultivated as ornamentals. Some species also have a long history of medicinal use for various ailments. The native species of Verbena are notorious for their frequent interspecific hybridization. Users of the present work should be aware that such hybrids, which are more or less intermediate in morphology between their avowed parental species, are not accommodated in the key to species below, but are to be expected to occur sporadically throughout the state. The following putative hybrids have been recorded from Missouri or are to be expected in the state:

V. ×blanchardii Moldenke (V. hastata × V. simplex) (to be expected)

V. ×deamii Moldenke (V. bracteata × V. stricta)

V. ×engelmannii Moldenke (V. hastata × V. urticifolia)

V. ×illicita Moldenke (V. stricta × V. urticifolia)

V. ×moechina Moldenke (V. simplex × V. stricta)

V. ×perriana Moldenke (V. bracteata × V. urticifolia)

V. ×rydbergii Moldenke (V. hastata × V. stricta)

V. ×stuprosa Moldenke (V. simplex × V. urticifolia) (to be expected)