We follow Cantino & Wagstaff (1998) in assigning the genera Acinos and Calamintha of Michigan Flora to a broadly defined Clinopodium.

1. Calyx with beard sparse or none in the throat; leaf blades ± ovate to reniform, broadly rounded to cordate at base; stems pubescent with long, usually dense spreading hairs.

C. vulgare

1. Calyx strongly bearded in the throat; leaf blades linear or ± elliptic and tapered to the base; stems pubescent with recurved hairs or essentially glabrous.

2. Blades of middle and upper leaves linear, sessile, entire; calyx lobes without cilia; stem, pedicels, and calyx (except for beard) glabrous.

C. arkansanum

2. Blades of middle and upper leaves ± elliptic, short-petiolate, often obscurely or irregularly toothed; calyx lobes ciliate; stem, pedicels, and calyx finely pubescent.

C. acinos