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..
Aromatic punctate herbs, or shrubs (a few tropical species trees), mostly with 4-sided stems and simple opposite leaves; stipules none. Flowers irregular, perfect, variously clustered, the inflorescence typically cymose, usually bracteolate. Calyx inferior, persistent, regular or 2-lipped, 5-toothed or 5-lobed (rarely 4-toothed), mostly nerved. Corolla with a short or long tube, the limb 4-5-lobed, mostly 2-lipped, regular in a few genera; upper lip 2-lobed, or sometimes entire; lower lip mostly 3-lobed. Stamens borne on the corolla-tube, typically 4 and didy-namous, sometimes 2 with or without staminodia, rarely equal; filaments separate, mostly slender, alternate with the corolla-lobes; anthers 2-celled, introrse, or con-fluently 1-celled, or sometimes of a single sac. Disk usually present, fleshy. Ovary 4-lobed or 4-parted, superior, each lobe or division with 1 mostly anatropous ovule; style arising from the center of the lobed or parted ovary, 2-lobed at the summit. Fruit of 4 1-seeded nutlets. Seed erect (transverse in Scutellaria); endosperm scanty, or usually none; embryo mostly straight; radicle short, inferior.
About 160 genera and 3200 species, of wide distribution in temperate and tropical regions. The family is also known as Lamiaceae. The foliage abounds in volatile oils.
A. Ovary 4-lobed, the style not basal; nutlets laterally attached. (Ajugeae.) Corolla-limb very irregular, apparently 1-lipped, or the other lip very short; stamens exserted. Upper lip of corolla short, truncate.
Upper lip of corolla 2-lobed, or all the lobes united into the lower lip.
Corolla-limb nearly equally 5-lobed.
Corolla-lobes spreading; stamens short-exserted.
Corolla-lobes declined; stamens long-exserted.
B. Ovary 4-parted, the style basal; nutlets basally attached.
* Calyx with a protuberance on the upper side. (Scutellariae.)
** Calyx not gibbous on the upper aide. (Stachyeae.)
Stamens and style very short, included in the corolla-tube. Anther-sacs parellel.
Anther-sacs, at least of the upper stamens, divergent. Stamens longer, not included in the corolla-tube.
† Corolla strongly 2-lipped; lips unlike, the upper concave. (a.) Anther-bearing stamens 4.
Posterior (upper) pair of stamens longer than the anterior. Anther-sacs parallel or nearly so.
Tall erect herbs; posterior stamens declined, anterior ascending.
Trailing herb; stamens all ascending under upper lip of corolla.
Calyx tubular, nearly equally 5-toothed, not 2-lipped; plant erect.
Calyx distinctly 2-lipped, or unequally 5-toothed. Trailing herb; calyx unequally 5-toothed.
Erect herbs: calyx 2- lipped.
Posterior pair of stamens shorter than the anterior. Calyx distinctly 2-lipped, closed in fruit.
Calyx 3-10-toothed, not distinctly 2-lipped, open in fruit. Calyx membranous, inflated in fruit, faintly nerved. Calyx nearly equally 5-toothed, or 5-lobed.
Calyx not membranous, not inflated in fruit, distinctly 5-10-nerved. Style-branches very unequal.
Style-branches equal, or nearly so. Anther-sacs transversely 2-valved.
Anther-sacs not transversely 2-valved, parallel or divergent. Nutlets 3-sided, truncate.
Calyx-teeth not spiny-tipped.
Nutlets ovoid, rounded above.
Calyx with a spreading 5-toothed limb.
calyx-limb not spreading.
Corolla-tube not longer than calyx; anther-sacs divergent.
Corolla-tube exserted; lower petioles very long; anther-sacs parallel.
(b.) Anther-bearing stamens 2.
Connective of the anther very long, bearing a perfect sac at one end, and a rudimentary one, or none, at the other.
Connective very short, the anther-sacs confluent. Calyx tubular, 15-nerved, equally 5-toothed.
Calyx ovoid-tubular, 13-nerved, 2-lipped.
†† Corolla 2-lipped, or regular; upper lip, when present, flat, or only slightly concave. (a.) Flowers in axillary whorls or clusters, or these forming terminal spikes.
Stamens curved, often converging, or ascending under the upper lip of the corolla. Anther-bearing stamens 2.
Anther-bearing stamens 4.
Corolla-tube upwardly curved, exserted.
Calyx 10-nerved, campanulate, about equally 5-toothed.
Calyx mostly 13-nerved, tubular, 2-lipped.
Stamens straight, often diverging. Calyx 15-nerved.
Anther-bearing stamens 4. Anther-sacs divergent.
Calyx equally 5-toothed; erect herbs.
Calyx 2-lipped; creeping herbs.
Anther-bearing stamens 2.
Corolla regular, 4-5- lobed.
Anther-bearing stamens 2; plants not aromatic.
Anther-bearing stamens 4; aromatic fragrant herbs.
(b.) Flowers in terminal panicled racemes or spikes; corolla 2-lipped.
Anther-bearing stamens 2; lower lip of corolla long, fimbriate; native.
Anther-bearing stamens 4; lower lip of corolla not fimbriate; introduced. Flowers racemose.
Flowers densely spiked.