[6] The staminode takes a variety of forms in the different species; while it is typically a long straight filament extending to the mouth of the corolla, some are longer and extremely hairy, giving the general appearance of an open mouth with a fuzzy tongue protruding and inspiring the common name of "beardtongue".

[6] Most penstemons form a durable woody stem (a caudex) and have persistent basal leaves, but some are fully deciduous perennials, the remainder being shrubs or subshrubs.

[8][9] In the view of penstemon expert Robert Nold the defining evolutionary characteristic of the genus is adaptation to drought, as demonstrated by their numbers and diversity in the interior west of North America.

[11] Floral colors are quite varied with white, blue, violet, purple, pink, magenta, and red all being common.

Genetic analysis by Andrea D Wolfe et al. indicates that while some of the previously identified subgenera are natural groupings, many are hopelessly confused.

[17][18] Linnaeus then included it in his 1753 publication, as Chelone pentstemon, altering the spelling to better correspond to the notion that the name referred to the unusual fifth stamen (Greek "penta-", five).

[20] The American members of the genus were extensively revised by David D. Keck between 1932 and 1957[21] and Richard Straw did similar work on the Mexican species slightly later.

This book was updated and republished with the Robin Lodewick in 1980 and continued to be an important source of information about the genus through the year 2000.

[26] The earliest development is somewhat shrouded in mystery; for instance Flanagan & Nutting's 1835 catalog mentions a 'Penstemon Hybridum' but does not describe it.

[27] By 1860, a half-dozen French growers are known to have developed hybrids, most notably Victor Lemoine, while in 1857 the German Wilhelm Pfitzer listed 24 varieties.

The Scottish firm of John Forbes first offered penstemons in 1870, eventually becoming the biggest grower in the world; in 1884 their catalog listed 180 varieties.

[29] The American Penstemon Society was formed in 1946 to promote both horticultural and botanical interest, and is now the International Cultivar Registration Authority for the genus.

[12] The following species and cultivars have gained the Royal Horticultural Society's Award of Garden Merit:-[31] Others include 'Dark Towers', developed by Dale Lindgren at the University of Nebraska.