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)