General: Perennial herb from a creeping rhizome; stems erect, 15-90 cm tall, simple or branched, 4-angled; strongly lemon-scented, but not pungent.
Leaves: Opposite, usually egg-shaped, 2-6 (9) cm long, 1-4 cm wide, more or less hairy, toothed, tips pointed or rounded, bases wedge-shaped to somewhat lobed; stalked.
Flowers: Inflorescence of a terminal head of 1 to 3 flower clusters and usually 1 to 3 axillary flower clusters below; lower bracts leaf-like, upper lanceolate or linear-lanceolate, hidden by the flowers; flower stalks hairy; corollas tubular, light purple, 4-lobed, the lobes nearly equal; calyces bell-shaped, nearly equally 5-toothed, hairy.
If more than one illustration is
available for a species (e.g., separate illustrations were provided for two
subspecies) then links to the separate images will be provided below.
Note that individual subspecies or varietal illustrations are not always available.
