This species is mainly represented in gardens by the following form:
f. humilior Sealy P. roezlii Hort., not Reg. – An evergreen, mat-forming subshrub 4 to 6 in. high; young stems clad with fine, spreading down. Leaves broad-elliptic to almost orbicular, 5⁄16 to 3⁄4 in. long, 1⁄4 to 7⁄16 in. wide, rounded to obtuse at the apex, cuneate at the base, bluntly toothed, dull green, leathery, glabrous; petioles 1⁄16 to 1⁄4 in. long. Flowering stems 3 to 5 in. long, with several pairs of reduced leaves in their lower part and terminated by two to eight flowers rather densely crowded together; pedicels 3⁄16 to 3⁄8 in. long, clad, like the upper part of the flowering stem, with fine glandular down. Calyx about 3⁄8 in. long, with bluntly acute to acuminate lobes. Corolla tubular-funnel-shaped, with scarcely spreading lips, bright cerise-crimson on the outside, about 11⁄4 in. long. Filaments of stamens glabrous; anthers densely bearded. Staminode (infertile stamen) hairy. Ovary glabrous, tapered into the style. Bot. Mag., n.s., t. 4.
The origin of the plant described above is unknown, but it was originally distributed earlier this century under the name “P. roezlii”, which properly belongs to a quite different plant. Under this erroneous name it received an Award of Garden Merit in 1931, and even today is still offered under it by some nurserymen. It is perhaps the commonest of the dwarf shrubby penstemons in gardens and one of the most decorative, bearing a profusion of vividly coloured flowers in May and June. It is hardy, provided it is planted in full sun and a well-drained soil, and is easily propagated by tip-cuttings in June, or even as late as September.
P. newberryi, in its typical state, resembles the plant described above in all essentials, but is more robust, with leaves up to 1 in. or slightly more long, and usually taller-growing, to about 11⁄2 ft. It is a native mainly of California, in the Sierra Nevada, from Tulare Co. northward; also farther north, in south-west Oregon. It was discovered by the geologist J. S. Newberry, who accompanied a railroad survey expedition in northern California and southern Oregon in the middle of the last century. It was in cultivation in Britain by 1872.
P. rupicola (Piper) Howell P. newberryi var. rupicola Piper; P. davidsonii Hort., in part, not Greene – This species is near allied to P. newberryi and was originally described as a variety of it, from a specimen collected on Mount Rainier. It differs in its prostrate, creeping habit; in its markedly glaucous, thick leaves, which usually have short, inconspicuous hairs on the midrib and main veins; in the fewer-flowered inflorescence; and in the more ventricose shape of the corolla. In the cultivated plant the colour of the flowers is pinker than in P. newberryi. Bot. Mag., t. 8660.
P. rupicola has a limited distribution from Washington to N. California. It was introduced to cultivation around 1910 and was distributed by Clarence Elliott’s Six Hills nursery as “P. davidsonii”, a name that belongs to a different, though related, species. It is hardy in a sunny place in well-drained soil.
The hybrid ‘Six Hills’ was the result of a cross between P. rupicola and P. eriantherus (cristatus), the second parent being an almost herbaceous species not treated here.