2. Urtica dioica L. (tall nettle)
Pl. 571 c–e; Map
2675
Plants
perennial, usually densely colonial from rhizomes. Stems 50–200(–250) cm long,
erect or ascending, unbranched or less commonly branched from the base,
sparsely to moderately pubescent with stinging hairs, otherwise glabrous or
sparsely to densely pubescent with short, nonstinging hairs. Stipules 5–15 mm
long, narrowly lanceolate. Leaf blades 4–15(–18) cm long, more or less the same
size along the stem (the upper leaves only slightly smaller than the others at
maturity), elliptic to lanceolate or narrowly to less commonly broadly ovate,
rounded to truncate or shallowly cordate at the base, the margins sharply and
relatively coarsely toothed (sometimes appearing doubly toothed, the main teeth
having smaller teeth along their margins), the surfaces glabrous or the
undersurface sparsely to moderately short-hairy, one or both surfaces often
also with scattered stinging hairs along the main veins, the undersurface
sometimes lighter green but not purplish-tinged; cystoliths rounded.
Inflorescences mostly longer than the subtending petioles, small globose
clusters, grouped into panicles with the branches of spikelike racemes, the
staminate and pistillate flowers in different inflorescences either on the same
or on different plants. Pistillate flowers with the 2 smaller sepals 0.8–1.2 mm
long, linear to narrowly lanceolate or oblanceolate, the 2 larger sepals
1.4–1.8 mm long, ovate to broadly ovate. Fruits 1.0–1.5 mm long. 2n=26, 52.
May–October.
Scattered north
of the Missouri River, sporadic farther south (nearly throughout the United
States but less abundant in the southeastern states; Canada, Mexico, Europe,
Asia). Bottomland forests, banks of streams and rivers, sloughs, and bases of
bluffs; also levees, ditches, railroads, roadsides, and moist disturbed areas.
Dennis Woodland
and his colleagues studied the biosystematics and taxonomy of the U. dioica
complex (Woodland, 1982a, 1982b; Woodland et al., 1982). They concluded that it
was best treated as a series of three subspecies with mostly nonoverlapping
ranges. Two of these occur in Missouri. The third, ssp. holosericea
(Nutt.) Thorne, occupies the western portion of the North American range of the
species, overlapping with ssp. gracilis in the northwestern and
Intermountain states. The ssp. holosericea differs from ssp. gracilis
in its more densely soft-hairy stems that also have more abundant stinging
hairs and in the more densely hairy undersurface of the leaves. Whereas, both
diploid and tetraploid cytotypes occur in ssp. gracilis, thus far ssp. holosericea
has only been documented as a diploid (2n=26).