This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol3", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Herbs, perennial by slender stolons or suckers, with erect or diffuse stems, petioled or sessile leaves, and small white or purple flowers, bracted and verticillate in dense axillary clusters. Calyx campanulate, regular or nearly so, 4-5-toothed, not bearded in the throat, the teeth obtuse or acute. Corolla funnelform-campanulate to cylindric, equalling or longer than the calyx, the limb nearly equally 4-cleft, or one of the lobes broader and emarginate. Perfect stamens 2, anterior, the posterior pair rudimentary, or altogether wanting; anther-sacs parallel. Ovary deeply 4-parted; style slender, 2-cleft at the summit. Nutlets truncate at the summit, narrowed below, trigonous, smooth, their margins thickened. [Greek, wolf-foot.]
About 15 species of the north temperate zone. Besides the following, two or three others occur in western North America. Type species: Lycopus europaeus L.
Calyx-teeth 4 or 5, ovate, shorter than the nutlets.
Base of the stem not tuberous; leaves ovate or ovate-lanceolate.
1. L. virginicus.
Base of the stem tuberous-thickened: leaves oblong to lanceolate.
2. L. uniflorus.
Calyx-teeth mostly 5, lanceolate or subulate, longer than the nutlets. Bracts minute; corolla twice as long as the calyx. Leaves sessile.
3. L. sessilifolius.
Leaves narrowed into a manifest petiole.
4. L. rubellus.
Bracts lanceolate or subulate; corolla not twice as long as the calyx. Leaves pinnatifid or deeply incised.
5. L. americanus.
Leaves merely coarsely dentate or serrate (lower rarely incised). Leaves oblong or oblong-lanceolate, serrate.
6. L. asper.
Leaves ovate, coarsely dentate.
7. L. europaeus.
Lycopus virginicus L. Sp. Pl. 21. 1753.
Perennial by long filiform leafy stolons, glabrous or puberulent; stem slender, erect or ascending, simple or branched, 6'-2° high. Leaves ovate or ovate-lanceolate, acuminate at the apex, sharply dentate, narrowed or cuneate at the base, petioled, or the upper sessile, dark green or purple, 1 1/2'-3' long, 1/2'-1 1/2' wide; bracts short, oblong; calyx-teeth 4, or sometimes 5, ovate or ovate-lanceolate, obtuse or subacute; corolla about 1" broad, narrow, nearly twice as long as the calyx, or longer; rudimentary posterior stamens minute; nutlets longer than or about equalling the calyx.
Lycopus uniflorus Michx. Fl. Bor. Am. 1: 14. 1803. Lycopus communis Bicknell, Britton Man. 803. 1901.
Green or sometimes purplish, mostly less pu-berulent than L. virginicus; stems rather slender, simple or sparingly branched, 4'-2 2/3° tall, rather acutely angled, tuberous at the base, the stolons rarely tuber-bearing. Leaves oblong or oblong-lanceolate, acute or acuminate at the apex, serrate, 3/4'-3 3/4' long, sessile or nearly so; calyx-teeth 4 or 5, triangular, ovate or ovate-oblong, rather obtuse; corolla about \\" long, less than twice as long as the calyx; rudimentary posterior stamens obsolete or minute; nutlets about as long as the calyx, oblique at the apex.
In low grounds, Newfoundland to British Columbia, North Carolina, Nebraska and Oregon. Summer and fall.
Lycopus membranaceus Bicknell, with thinner, often coarsely-toothed, longer-petioled and larger leaves, appears to be a race of this species.