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.
Cantino, P. D. 1982. A monograph of the genus Physostegia (Labiateae). Contr. Gray. Herb. 211: 1-105.
Key to Texas Physostegia & Species Descriptions
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