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This spreading, sometimes invasive perennial spreads by rhizomes. A member of the nettle family, Physostegia virginiana has square stems. The common name comes about from the way that the individual flowers of this plant will stay in a new position if moved horizontally around the flower stalk. This is because each flower has a hinge attaching it to the flower stalk. Physostegia virginiana has mid-green leaves. The flowers are usually produced from mid summer for a long period, into early autumn. Flower colour varies from dark purple to bright pink and occasionally white.

The Latin name Physostegia is a reference to the bladder like shape of the calyx.