25. Pycnanthemum Michx. (mountain mint)

Plants perennial herbs, with slender rhizomes. Stems erect or ascending, bluntly to sharply 4-angled, unbranched or branched mostly toward the tip, glabrous or more commonly hairy, sometimes only on the angles. Leaves sessile or short-petiolate, the petiole usually winged, at least toward the tip. Leaf blades variously linear to lanceolate, elliptic, or ovate, rounded to angled or tapered at the base (mostly rounded to cordate in P. muticum), angled or tapered to a usually sharply pointed tip, the margins entire or finely few-toothed, the surfaces glabrous or variously hairy, sometimes densely so, in a few species appearing whitened, the undersurface also with usually conspicuous, sessile glands. Inflorescences terminal, composed of dense, headlike (spherical or depressed-globose) clusters of numerous flowers at the stem or branch tips, these usually grouped into relatively flat-topped to broadly rounded, dense or more loosely branched panicles, the branches visible or mostly obscured. Bracts similar to the foliage leaves (except in P. tenuifolium with much smaller, broader bracts), but sometimes smaller. Bractlets usually 1 or 2 per flower cluster, much smaller than the bracts (except in P. tenuifolium with the bractlets not much smaller than the bracts), variously shaped. Calyces actinomorphic or zygomorphic and 2-lipped, lacking a lateral projection, more or less symmetric at the base, bell-shaped, the tube 10–13-nerved, 5-lobed, the lips and/or lobes shorter than the tube, similar or dissimilar in size and shape, triangular to narrowly triangular, not spinescent, not becoming enlarged or papery at fruiting. Corollas zygomorphic, white to pale pinkish-tinged or pale lavender, the lower lip with reddish purple to purple spots or mottling, the outer surface moderately to densely short-hairy, also with sessile glands, the tube funnelform, sparsely hairy in the throat, relatively deeply 2-lipped, the lobes slightly shorter than the tube, the upper lip shorter than to about as long as the lower lip, entire or shallowly notched, slightly concave, the lower lip spreading to arched, 3-lobed, the central lobe longer than the pair of lateral lobes. Stamens 4, sually exserted, the lower pair with slightly longer filaments than the upper pair, all relatively straight and not ascending under the upper corolla lip, the anthers small, the connective very short, the pollen sacs 2, parallel, usually light to dark purple. Ovary deeply lobed, the style appearing nearly basal from a deep apical notch. Style exserted, more or less equally 2-branched at the tip. Fruits dry schizocarps, separating into usually 4 nutlets, these 0.7–2.2 mm long, obovoid or oblong-ellipsoid, rounded or bluntly pointed at the tip, somewhat 3-angled, the surface dark brown to nearly black, glabrous or minutely hairy toward the tip, finely pebbled or finely pitted. Twenty species, North America.