Narrow-leaf mountain-mint

Pycnanthemum tenuifolium, the narrow-leaf mountain-mint or slender mountain-mint, is an aromatic perennial herb in the Lamiaceae family native to central and eastern North America from Maine and Ontario west to Minnesota and south to Texas and Florida. Plants grow 0.6 to 0.9 metres tall on slender, square, wiry, much-branched stems that are nearly glabrous and frequently flushed with green. The leaves are opposite, linear to narrowly lanceolate, 2 to 5 centimetres long and only a few millimetres wide, sessile, entire-margined, and emit a strong minty fragrance when crushed. Flowering occurs from midsummer through early autumn; the inflorescence consists of numerous dense, flat-topped, hemispherical heads of small white flowers, often spotted with purple, surrounded by silvery-bracted involucres that give the plant a frosted appearance. The fruits are smooth nutlets enclosed in the persistent calyx. The species favours dry to moist open habitats including prairies, rocky woods, pine barrens, and wet thickets.