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).