This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
Biennial or perennial herbs, rarely shrubby. Leaves simple, alternate, the lower ones tufted and petiolate. Flowers in long terminal bracteate racemes. Calyx deeply 5-lobed. Corolla decimate, tubular, irregularly campa-nulate or ventricose, the lower central lobe being longest. . Stamens 4, included; anthers cohering in pairs. Fruit capsular, opening in 2 valves. Upwards, of a dozen species have been described, chiefly from the Mediterranean region. The name is from digitate, a finger-stall or thimble, the shape of the corolla.
Fig 192. Digitalis purpurea. (1/4 nat. size.)
1. D. purpurea (fig. 192). Foxglove. - This common indigenous biennial species is the handsomest of the genus, but it is only suitable for large gardens, shrubberies, or parks, where it may be grown in masses in a semi-wild state. Leaves slightly cottony. Flowers in the common variety purple speckled with ocellated spots; a white and a rosy variety are occasionally seen.
D. Thapsi is a perennial species resembling the last, with decurrent leaves and rather smaller purple spotted flowers on distinct peduncles.
D. ferruginea, D. lutea, D. grandiflora, and D. ochroleuca have rusty creamy or pale yellow flowers, and are only worthy of a place in large collections.