There are several species that are given the common name of skullcap and they can be difficult to distinguish. All are sometimes referred to as helmet dlowers. All are members of the mint family and have flowers that are usually violet or blue. Like all mints, they have stems that are square in cross-section.

The perennial downy skullcap grows about 2-3 feet tall and is covered with minute whitish hairs. It is one of the showiest of the skullcap species. The deep blue flowers are found in clusters (racemes) of several flowers. These flower spikes can be up to six inches in length. Each flower is 2-lipped and superficially resembles a snapdragon. The upper lip of the corolla is hood-like with lateral margins that are curled back, while its lower lip is larger and broader. There is a conspicuous patch of white in front of the throat of the flower. The outer surface of the flowers is finely pubescent. Bumblebees are the primary pollinators.

The fruit is an oddly shaped capsule that resembles a dish or saucer. The genus name is derived from the Latin word Scutella, meaning, a small dish or platter. It is this capsule and perhaps the helmet shape of the flower that gives the plant the common name skullcap. Each capsule contains 2-4 nut-like seeds.

The plant branches only at the top. The leaves are oval-shaped and longer than those of the related hairy skullcap (S. elliptica). These leaves are about 3 inches long and 1½ inch wide. Only the underside of the leaves is pubescent.

The downy skullcap grows in dry woods and clearings from Iowa to southwestern New York (where it is endangered) and New Jersey southwards. It can be found growing throughout Western Pennsylvania. The blooming period is June to September. It is also called the hoary skullcap. This and related plants are commonly used in herbal medicine, but potentially severe side effects can come from overuse.