With some 270 species, "Penstemon" is the largest genus endemic to North America, with examples to be found in every state in the continental U.S. Penstemons are particularly beloved by rock gardeners, but as Panayoti Kelaidis points out in his foreword, they belong in every garden, since "one penstemon or another will thrive in virtually any microclimate a garden can contrive, from hot, desert exposures to dank shade."