Lamiaceae
This is a large, well-known family. Most (not all) of our species have a 4-angled ("square") stem (but square stems occur in several other families as well), and all have simple opposite leaves. The ovary is ± strongly 4-lobed, producing (if all ovules are fertilized) 4 nutlets. Most species contain aromatic oils, associated with resinous dots on the leaves and other organs. In most species the flowers are in small, sometimes dense, axillary inflorescences, but these are crowded toward the summit of the stem in some species, forming what appears to be a terminal head or spike.
The corolla is typically bilaterally symmetrical and 2-lipped, but the upper lip may be much reduced. In some genera the flowers are essentially radially symmetrical (regular). The calyx ranges from 2-lipped to regular and is often easier to use in keys as it is more persistent and easily seen than other flower parts. A dense zone of hairs forming a beard in the throat of the calyx (at summit of tube) is usually conspicuous when present, visible between the bases of the calyx lobes. The keys here do not stress the relative length and position of the stamens or the shape of the corolla lips, as these characters are rarely well displayed on pressed specimens, and most collectors fail to record such helpful information on their labels. The fertile stamens are 4 in most genera, but 2 in a few (sometimes with staminodia).
A few cautions may help to interpret the keys, which as always are artificial. Before concluding that flowers have only 2 fertile stamens, examine enough fresh ones to be sure that anthers have not simply fallen off. Before measuring flower (or corolla) length, or extent of exsertion of corolla beyond the calyx teeth, be sure that the corolla has not separated from the receptacle with its base clinging higher in the calyx tube.
Several genera in which certain characters used in the keys may be ambiguous or easily misinterpreted are entered at more than one place. Enough characters have generally been included in the keys so that after trying both choices in a puzzling couplet, the user should find that only one of them leads to a reasonable conclusion.
1. Corolla (but not necessarily calyx) radially symmetrical or nearly so (slightly oblique), with 4-5 lobes of about equal length (if not always width).
2. Leaves entire (or with an occasional irregular tooth).
3. Flowers white (usually dotted with color), in small involucrate heads borne in a corymb-like inflorescence; ovary deeply 4-lobed, with style inserted all the way to the base; stems and pedicels glabrous or with non-glandular pubescence.
Pycnanthemum (in part)
3. Flowers blue, mostly pediceled in axils of leaves or bracts (or on 1-3-flowered peduncles); ovary shallowly lobed, with terminal style; stems and pedicels with glandular pubescence.
Trichostema (in part)
2. Leaves with blades regularly toothed or lobed for at least half their length.
4. Stamens 2; flowers all sessile in axillary clusters; bruised foliage not (or very slightly) aromatic; nutlets with corky rims or teeth at summit; corolla white.
4. Stamens 4; flowers short-pediceled, whether axillary or on terminal spikes; bruised foliage strongly aromatic; nutlets smooth or (Perilla) reticulate; corolla white to purple.
5. Flowers clearly in terminal and axillary racemes, the solitary pedicels quite visible though shorter than the calyx and subtending bract; leaf blades coarsely toothed, ca. 1.5 times as long as broad, or shorter, and also less than 1.5 times as long as petiole; annual.
5. Flowers densely whorled in terminal spike-like and/or axillary clusters, appearing not at all racemose; leaf blades various; perennial.
6. Corolla over 5 mm long, 5-lobed; flowers all in terminal spikes at least 1-5 cm thick; plants without creeping rhizomes.
Agastache (in part)
6. Corolla 5 (-5.7) mm long or less, 4-lobed; flowers in axillary clusters or if in terminal spikes, these less than 1.5 cm thick; plants colonial with long-creeping rhizomes.
1. Corolla clearly bilaterally symmetrical, 1- or 2-lipped.
7. Upper lip of corolla much reduced or apparently absent (deeply split, each half connate with lower lip); style not fully gynobasic (though ovary 4-lobed).
8. Corolla deep blue (rarely pink or white); bracts of inflorescence ovate or obovate; lower lip of corolla 3-lobed, the middle lobe sometimes notched but scarcely (less than twice) as large as lateral lobes.
8. Corolla pink-magenta (rarely white); bracts of inflorescence narrowly liner-lanceolate; lower lip of corolla 5-lobed, the middle lobe much larger than the 2 tiny lobes on each side of the lip.
7. Upper lip of corolla well developed and evident; style gynobasic (inserted deep into the base of the 4 lobes).
9. Calyx of essentially 2 obtuse lips, the upper with a ± erect, flattened to conical, transverse protuberance; corolla blue.
9. Calyx various but without a protuberance; corolla various.
10. Flowers in dense heads or whorls subtended by 4 or more leafy bracts of similar and conspicuous size.
11. Calyx essentially regular, teeth all about the same length.
11. Calyx clearly bilabiate; the upper 3 teeth much longer than the lower two.
Blephilia (in part)
10. Flowers in heads or not, but subtending bracts inconspicuous or only 1 or 2.
12. Most if not all flowers in distinct terminal inflorescences (heads, spikes, or racemes) at the ends of stems and leafy branches, the uppermost whorls of flowers exceeding any bracts.
13. Inflorescence ± corymbose; flat-topped or dome-like and branched, with flowers or few-flowered heads on evident stalks.
14. Calyx densely bearded in the throat; leaf blades less than 2.8 (-3) cm long, ± truncate or rounded to a distinct petiole; calyx lobes and bracts in the heads ± deep red-purple.
14. Calyx naked in the throat; leaf blades over 2.8 cm long, or linear, or nearly or quite sessile (or all of these); calyx lobes and bracts green to white-pubescent (at most pink-tipped).
Pycnanthemum (in part)
13. Inflorescence a raceme, panicle, elongate spike, or flowers sessile to short-pediceled in a ± dense head.
15. Inflorescence racemose or paniculate, each mature flower on a pedicel greatly exceeding its minute bract and distinctly longer than the calyx; lower lip of corolla yellow, fringed; fertile stamens 2, long-exserted.
15. Inflorescence ± spicate or of crowded heads, the pedicels none or shorter than both bracts and calyx; lower lip rarely yellow, rarely fringed (never both); fertile stamens 4 (except in Blephilia and Salvia).
16. Fertile (anther-bearing) stamens 2 [see also notes in text on these species].
17. Flowers sessile or nearly so, numerous in dense whorls at each node of inflorescence, at least the uppermost 3-4 whorls contiguous (forming a many-flowered, sometimes tiered, head); native in moist forests, thickets, and drier openings.
Blephilia (in part)
17. Flowers on readily visible pedicels ca. 2-4 (-6) mm long, only 2-12 developed at each node of the inflorescence, not crowded into heads (the internodes of inflorescence apparent); in our area all of disturbed ground and fields.
16. Fertile (anther-bearing) stamens 4.
18. Leaves entire or nearly so (teeth, if any, obscure and broadly rounded).
19. Calyx densely and conspicuously bearded in the throat, strongly 2-lipped (upper lip with 3 short teeth, lower lip deeply bifid); leaves less than 1.5 cm long.
19. Calyx scarcely or not at all bearded in the throat and (except in Prunella) with 5 elongate (over 12.5 mm) teeth or lobes (i.e., regular or only weakly 2-lipped); leaves all or almost all over 1.5 cm long.
20. Leaf blades ± linear, over 4 times as long as broad.
21. Stem and calyx finely pubescent on all sides; mature stamens well exserted beyond corolla; lower lip of corolla distinctly longer than the upper lip.
21. Stem and calyx glabrous or nearly so; mature stamens not exceeding upper lip of corolla; lower lip of corolla about equaling the upper lip.
20. Leaf blades less than 4 (very rarely 4.5) times as long as broad.
22. Floral bracts linear-setaceous; upper lip of calyx with 3 well-developed narrow lobes similar to those of lower lip.
Clinopodium (in part)
22. Floral bracts broadly ovate, overlapping, obtuse or rounded (except for short-acuminate or mucronate tip); upper lip of calyx with 3 very short (less than 1 mm) teeth or excurrent bristles.
18. Leaves clearly and regularly toothed.
23. Bracts subtending flowers ± orbicular to reniform, entire, with an apical awn, uniform throughout the inflorescence.
23. Bracts subtending flowers linear to ovate, usually at least the lowest ± toothed, the apex awned or not, rapidly reduced in size towards the apical portion of the inflorescence.
24. Flowers only 2 per node of the inflorescence (a simple or branched elongate slender raceme or spike); calyx at flowering time with obscure nerves (at fruiting, reticulate-veiny and inflated), puberulent; leaves and internodes glabrous.
24. Flowers 3 or more at all or most nodes of the inflorescence; calyx strongly longitudinally nerved, variously glabrous or pubescent; leaves (at least beneath) and usually stem pubescent.
25. Calyx regular, with essentially equal lobes, the tube 5-15-nerved.
26. Calyx lobes with terete, non-green, spiny tip about half or more the total length of the lobe.
Galeopsis (in part)
26. Calyx lobes with non-green tip, if any, much less than half the length of the lobe.
27. Nerves of calyx 15; leaves (except sometimes the uppermost) with petioles ca. 1-6 (-9) cm long.
Agastache (in part)
27. Nerves of calyx 5 or 10; leaves sessile or with petioles up to 2.2 (-2.8) cm long.
Stachys (in part)
25. Calyx ± 2-lipped, with upper lobe distinctly broader or with some sinuses distinctly deeper than the others, the tube 15-nerved.
28. Blades (at least of middle and upper leaves) ± tapered to base; calyx nearly glabrous (except for hairs on nerves and margins), with upper lobe distinctly broader than the other 4 and appearing at least slightly longer, with (in common species) a small hairy callus at each sinus; corolla blue or pink (rarely white).
28. Blades subcordate or cordate; calyx softly pubescent, with all lobes of ± equal width but upper 2 lobes longer (at least in part because of deeper sinuses, which lack a callus); corolla white, dotted with purplish.
12. Most or usually all flowers in distinct axillary inflorescences subtended by leaves or leafy bracts that exceed them, the intact stem usually ending in small leaves (not flowers).
29. Calyx lobes each tipped with a rigid, terete, non-green spine ca. half as long as the rest of the lobe, or longer.
30. Lobes of calyx 10, the spine with recurved tip; stems and leaves (especially beneath) densely white-tomentose.
30. Lobes of calyx 5, the spine straight; stems and leaves glabrate or with usually straight hairs.
31. Leaves, at least on middle and lower part of stem, 3-lobed; calyx tube 5-nerved; anthers opening longitudinally (sacs parallel).
31. Leaves toothed but not lobed; calyx tube 10 (-15)-nerved; anthers opening transversely (sacs divergent).
32. Calyx ca. 5-7 mm long, about equaling the corolla, the lobes ± erect; corolla only short-pubescent above; nutlets sharply 3-angled, pubescent on apex; internodes finely pubescent, the longest hairs scarcely 0.5 mm.
32. Calyx mostly 8-14 (-17) mm long at maturity, shorter than the corolla, the lobes becoming widely spreading; corolla with upper lip usually long-pilose above; nutlets rounded (very obscurely angled), glabrous throughout; internodes in common species with stiff spreading-retrorse hairs.
Galeopsis (in part)
29. Calyx lobes variously shaped, but without spiny tips.
33. Tube of calyx with 5 (-10) strong nerves (weaker nerves may also be present); throat of calyx naked.
34. Leaf blades entire, linear to narrowly elliptic and tapered to the base.
35. Pubescence all eglandular; leaves with prominent dark resinous dots on both surfaces; calyx nearly regular; stamens included in the corolla.
35. Pubescence of stem (especially toward summit) and calyx including many short gland-tipped hairs; leaves with scarcely visible resinous dots beneath; calyx strongly 2-lipped; stamens long-exserted.
34. Leaf blades regularly toothed or crenate, reniform to ovate, mostly truncate to subcordate at base.
36. Flowers and fruit on definite pedicels ca. 2 mm or more long.
Melissa (in part)
36. Flowers and fruit sessile or nearly so.
37. Flowers yellow; plants perennial by long-creeping leafy stolons.
37. Flowers purple or white; plants tufted annuals or perennials spreading by short rhizomes.
33. Tube of calyx with 13-15 strong nerves; throat of calyx bearded or naked.
38. Calyx with beard sparse or none in the throat; leaf blades ± ovate to reniform, broadly rounded to cordate at base.
39. Floral bracts elliptic, mostly with distinct lateral veins.
Melissa (in part)
39. Floral bracts linear-setaceous, at most the midnerve evident.
40. Leaves entire (or very obscurely toothed); stem pubescent with long, usually dense spreading hairs.
Clinopodium (in part)
40. Leaves prominently crenate-toothed; stem (except sometimes at nodes) glabrous or very minutely pubescent.
38. Calyx strongly bearded in the throat; leaf blades linear or ± elliptic and tapered to the base.
41. Corolla scarcely if at all (at most 1-2 mm) longer than the calyx lobes; fertile stamens 2.
41. Corolla 2-8 mm longer than the calyx lobes; fertile stamens 4.
Clinopodium (in part)
Citation:
MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. March 16, 2025
https://mifloradev.lsa.umich.edu/flora-demo/#/family/Lamiaceae