Plants perennial herbs, with vertical rootstocks and sometimes slender rhizomes. Stems erect or ascending, bluntly to sharply 4-angled, usually with thickened, blunt, often pale angles, usually unbranched, glabrous or rarely minutely hairy at the very tip. Leaves progressively reduced from the stem base to its tip, sessile or the lowermost leaves short- to long-petiolate, the petiole winged, the petiolate leaves usually withered and shed by flowering time. Leaf blades variously linear to narrowly oblong, narrowly lanceolate, narrowly elliptic, or lanceolate, tapered to the base, sometimes narrowly truncate or with a pair of small, clasping auricles at the very base, tapered to a sharply pointed tip, the margins variously entire, somewhat wavy, or with bluntly or sharply pointed teeth, the surfaces glabrous, but usually with sparse, inconspicuous, sessile glands. Inflorescences terminal and occasionally also axillary, of elongate spikelike racemes, the terminal racemes sometimes in clusters of few to several from the inflorescence base, more or less continuous (except sometimes toward the base, the flowers 2 per node (solitary in the axil of each bract), sessile and short-stalked (to 2.5 mm) in the same inflorescence. Bracts 2–7 mm long, narrowly lanceolate to ovate, those at the inflorescence base occasionally to 20 mm long and linear; bractlets absent. Calyces actinomorphic or nearly so, often slightly oblique at the tip, lacking a lateral projection, more or less symmetric at the base, bell-shaped, the tube faintly to very faintly 10-nerved, 5-lobed, the lobes shorter than the tube, similar in size and shape, triangular to broadly lanceolate, not spinescent, becoming slightly enlarged and somewhat leathery at fruiting. Corollas zygomorphic, white, lavender, pale purple, pale pink, pink, or pinkish purple, the lower lip (and sometimes upper lip and throat) usually with reddish purple to purple spots or fine mottling, the outer surface glabrous or sparsely to moderately pubescent with minute hairs, the tube asymmetrically funnelform (somewhat pouched on the lower side above the base), 2-lipped, the lips shorter than the tube, the lips about the same length, the upper lip entire or shallowly notched, slightly concave, the lower lip spreading to arched, 3-lobed with a broad central lobe (this sometimes notched or slightly irregular along the margin) and 2 small lateral lobes. Stamens 4, not exserted, the lower pair with slightly longer filaments than the upper pair, all ascending under the upper corolla lip, the anthers small, the connective very short, the pollen sacs 2, parallel or nearly so, attached at their midpoints, dark purple. Ovary deeply lobed, the style appearing nearly basal from a deep apical notch. Style not exserted, more or less equally 2-branched at the tip. Fruits dry schizocarps, separating into usually 4 nutlets, these 2–4 mm long,ovoid to broadly ellipsoid, angled at the tip, 3-angled, the angles often ridged, the surface brown, glabrous, finely pebbled or smooth. Twelve species, North America.

The species of Physostegia are variable and can be very difficult to distinguish. Cantino’s (1982) monograph of the genus included a key to species that requires 25 couplets to discriminate between only12 species.