Description:
Stiffly erect perennial herbs to 2 m high, usually arising from rhizomes. Basal leaves over wintering as a rosette, but soon deciduous; cauline leaves opposite sessile, glabrous. Flowers arranged in single or branched bracteate spike-like racemes. Calyx regular, campanulate, weakly 10-nerved, if at all, the 5 lobes more or less alike. Corollas 2-lipped, white, variously pink, deep lavender to reddish, the lips about equal in size. Stamens 4; anthers purple to nearly white. Ovary deeply 4-lobed. Nutlets 1-4, weakly 3-sided, brown and smooth at maturity. Base chromosome number, x = 19.
The generic name derives from two Greek words, physa (a bladder) and stege (a covering), which alludes to the calyx, which at maturity becomes inflated and covers the fruit.
As treated by Cantino (1982), a wholly North American genus of 12 species, one of these (P. virginiana ) with two intergrading morphogeographical varieties. The species, for the most part, are very similar and difficult to sort out by the beginner. All of the species are attractive plants, and Physostegia virginiana , the most widespread and common species of the genus, was taken into cultivation in Europe as early as 1674 (Cantino, 1982), cultivars of which were probably introduced into the U.S. where it has become a common garden perennial, persisting here and there as an escapee. The following key is based upon Texas plants only.