Stems ± erect, pyramidally much branched, pubescent, base glabrescent. Petiole slender, 0.5-2(-4) cm; leaf blade ovate, 1-5(-6.5) × 0.8-4(-5) cm, ± membranous or herbaceous, adaxially villous, abaxially villous along veins, base rounded to subcordate rarely obtuse or acute, margin serrate-crenate to obtusely serrate, apex acute to obtuse. Verticillasters 2-14-flowered, short pedunculate; bracts leaflike, much smaller than leaves, villous, ciliate. Pedicel ca. 4 mm. Calyx campanulate, ca. 8 mm, villous outside, villous inside apically; upper lip short 3-denticulate or ± undulate, teeth with short erect apices; lower lip slightly longer than upper, teeth narrowly triangular, apex spinescent. Corolla creamy white, 1.2-1.3 cm, villous outside; upper lip emarginate; middle lobe of lower lip obliquely spreading, rounded. Fl. Jun-Aug.
Lemon Balm rarely naturalizes in Illinois (see Distribution Map), where it is not native. This plant was introduced from Europe into North America as a culinary and medicinal herb. It is still cultivated in gardens and sometimes it is grown commercially. Escaped plants are typically found in such habitats as thickets, fence rows, abandoned homesites, vacant lots, areas along roadsides, banks of ponds, floodplain areas along drainage canals, and waste areas. Areas with a history of disturbance are preferred. Lemon Balm is especially likely to naturalize in urban and suburban areas, as this is where most cultivated plants occur.