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..
Annual or perennial glabrous pubescent or hirsute herbs, with small or rather large purple yellow red or white flowers, loosely verticillate-clustered in terminal dense or interrupted spikes, or also in the upper axils. Calyx mostly campanulate, 5-10-nerved, 5-toothed, the teeth nearly equal in our species. Corolla purple in our species, its tube narrow, not exceeding the calyx, the limb strongly 2-lipped; upper lip erect, concave, entire or emarginate; lower lip spreading, 3-cleft, the middle lobe broader than the lateral ones, sometimes 2-lobed. Stamens 4, didynamous, ascending under the upper lip of the corolla, the anterior pair the longer, sometimes deflexed or twisted after anthesis; anthers contiguous in pairs, 2-celled, the sacs mostly divergent. Ovary deeply 4-lobed; style 2-cleft at the summit into subulate lobes. Nutlets ovoid or oblong. [Greek, a spike, from the spicate inflorescence.]
About 160 species, of wide geographic distribution in the north temperate zone, a few in South America and South Africa. Besides the following, some 20 others occur in the southern and southwestern United States. Type species: Stachys germanica L.
1. Leaves, or some of them narrowed or acute at the base, linear to oblong or lanceolate.
Stem glabrous or nearly so, sometimes sparingly hirsute on the angles; leaves nearly or quite entire. Leaves 1"-2 1/2" long, linear.
1. S. hyssopifolia.
Leaves 2"-s" wide, oblong to linear-oblong.
2. 6. atlantica.
Stem retrorsely hirsute; leaves serrate.
Stem hirsute only on the angles; leaves slightly pubescent.
3. S. ambigua.
Stem densely hirsute all over; leaves densely pubescent.
4. S. arentcola.
2. Leaves rounded, cordate or truncate at the base, oblong, ovate or lanceolate. Leaves all subsessile or short-petioled.
Glabrous or very nearly so, the stem-angles sparsely bristly.
5. S. latidens.
Stem retrorsely hirsute; leaves pubescent. Leaves lanceolate to oblong-lanceolate.
6. S. palustris.
Leaves ovate to oblong-ovate.
Leaves, at least the lower, slender-petioled. Stem glabrous, or nearly so.
8. S.. tenuifolia.
Stem retrorsely hirsute or villous.
Petioles less than one-fourth as long as the blades. Pubescence hirsute.
9. S. aspera.
Pubescence short, dense.
10. S. salvioides.
Petioles, at least those of lower leaves, about one-half as long as the deeply cordate blades.
11. S. cor data.
Plant low, hirsute.
12. S. arvensis.
Plant tall, densely villous.
13. S. germanica.
Perennial, glabrous or very nearly so throughout, sometimes slightly hirsute at the nodes; stem slender, usually branched, erect or nearly so, 1°-1 1/2° long. Leaves thin, linear, acute at both ends, or the uppermost rounded at the base, short-petioled or sessile, entire, or sparingly denticulate with low teeth, 1-2' long, 1"-2 1/2" wide, the uppermost reduced to short floral bracts; clusters few-several-flowered, forming an interrupted spike; calyx glabrous or slightly hirsute, 2"-3" long, its teeth lanceolate-subulate, nearly as long as the tube; corolla about 7" long, light purple, glabrous.
In fields and thickets, Massachusetts to Florida, Indiana, Michigan and Virginia. July-Sept.