Article from Bean's Trees and Shrubs Hardy in the British Isles
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'Penstemon heterophyllus' from the website Trees and Shrubs Online (treesandshrubsonline.
A subshrub usually under 11⁄2 ft high, the stems, leaves, and inflorescences either glabrous or slightly downy. Leaves opposite, sessile, linear or lanceolate, 1 to 4 in. long, 1⁄8 to 1⁄4 in. wide, sessile, green or more rarely glaucous. Flowers lavender-blue at the mouth, purplish red at the base, 1 to 11⁄4 in. long, borne in the axils of reduced leaves at the ends of the season’s shoots singly or in twos; tube narrow, somewhat inflated and expanded at the apex. Anthers hairy on the margin; sterile stamen glabrous. Bot. Mag., t. 3853.
Native of California; discovered by Douglas and introduced by him in 1828. It is a beautiful species in its best-coloured forms but rather tender and intolerant of winter wet.