Approximately 270 species of evergreen or rarely deciduous perennials and evergreen shrubs or subshrubs from the mountains of Guatemala north to Alaska. The greatest concentration of species occurs in the Great Basin where each mountain range seems to contain some special form, subspecies, or endemic taxon. They have simple, often toothed leaves in opposite pairs and usually terminal racemes or thyrses of tubular five-lobed and more or less two-lipped flowers in a wide colour range.
This largely garden-worthy genus contains some choice plants for the rock garden, raised bed, scree or alpine house, a few of which are regularly commercially available. Although a few species grow in moist meadows (primarily in the subsection Proceri), most are denizens of open screes, steppe, desert or prairies where there is little shade, much air circulation and little competition from other plants. Penstemons do best on loose scree with relatively high nutrient content and full exposure to the sun. Their longevity is often proportional to drainage, if not dryness, both in the growing season and during the winter months. Culturally, penstemons might be grouped in four general categories:
[1] those from wetter portions of eastern North America that tolerate average rock garden conditions, comparable, say, to scree where primulas of the Auricula section or silver saxifrages might be accommodated; e.g. Penstemon hirsutus 'Pygmaeus'. [2] Species from the maritime mountains of the Pacific Northwest, and high alpine species from the Rockies and Sierras that need attention to drainage and coolness comparable to androsaces or Porophyllum saxifrages, e.g. Penstemon rupicola or P. hallii. [3] Montane species and those from cool steppe that require sharp drainage and some protection from wetness in winter but can be grown in rock gardens in most regions provided they have full sun, e.g. Penstemon pinifolius. [4] Desert-steppe species requiring not only protection from excess moisture most seasons of the year (conditions comparable to Oncocyclus or rare Juno iris) but some measure of heat in the growing season. This group demands alpine house or bulb frame treatment in wet climates; e.g. Penstemon gairdneri. Many taxa are given a range
(e.g. 3-4) suggesting that plants of the taxon may tolerate either state, or else that the plant occurs over a wide range in nature, and genotypes within the species might adapt to either extreme depending upon provenance. Sections and subsections are listed immediately after the species name, since plants within a section often have a family resemblance to one another and frequently require similar culture as well. Propagation by seed in spring or cuttings in late summer. (summer-flowering unless otherwise stated)
a, P. baccharifolia; b, P. campanulatus; c, P. gracilis;
a, P. heterophyllus; b, P. humilis; c, P. ovatus; d, P. richardsonii;