Pennsylvania's skullcaps are prennial, mostly rhizomatous herbaceous plants with square stems and opposite pairs of leaves.  Flowers are mostly blue or violet and in some species can occasionally be pinkish or white.  These flowers are tubular and have two-lipped corolla with a three-lobed lower lip.  Calyx is strongly two-lipped.  All our species are mostly mammal-resistant as the leaves are bitter tasting.