The most apparent differences between Digitalis purpurea and other foxglove species lie in their physical form. Common Foxglove is a robust biennial or short-lived perennial, typically reaching heights of 4 to 6 feet (1.2 to 1.8 meters). Its flowers are iconic: large, pendulous, and tubular, arranged in a one-sided spike (raceme). The inside of the blossoms is heavily spotted with maroon or purple on a background that is most commonly a striking purple-pink, though white cultivars exist. Its leaves are broadly ovate, softly hairy, and form a large basal rosette in the first year, with smaller alternate leaves on the flowering stem.
In contrast, other species exhibit significant variations. The Straw Foxglove (Digitalis lutea) is much smaller, with slender stems bearing small, creamy-yellow, unspotted flowers. The Grecian Foxglove (Digitalis lanata), another medically important species, has smaller, buff-brown flowers with a distinctive white, woolly (lanate) lower lip and veins. Its overall stature is generally more slender and less imposing than that of D. purpurea.
Digitalis purpurea is native to most of temperate Europe, specifically thriving in acidic soils. It is a classic pioneer species of disturbed ground, commonly found in woodland clearings, embankments, and burned areas. Its preference for partial shade and well-draining, slightly acidic substrates is a key ecological identifier.
Other foxglove species occupy distinct ecological niches. Digitalis grandiflora (Yellow Foxglove) is native to central Europe and Asia, preferring calcareous (alkaline) soils and sunny meadows. Digitalis obscura (Sunset Foxglove) is a drought-tolerant species from Spain and Morocco, adapted to dry, rocky hillsides in full sun, a habitat vastly different from the moist, partially shaded haunts of the Common Foxglove.
All parts of all foxglove plants are highly toxic due to the presence of potent cardiac glycosides. However, the specific type and concentration of these compounds vary between species. Digitalis purpurea primarily contains digitoxin and gitoxin. These compounds are powerful and were the original source of the digitalis drug used to treat heart conditions.
Other species produce different glycoside profiles. Digitalis lanata (the Woolly Foxglove) is the primary commercial source for digoxin, a glycoside that is more easily absorbed and eliminated by the body than those from D. purpurea, making it more suitable for modern pharmaceutical production. This difference in secondary metabolites is a crucial biochemical distinction with significant medical implications.
Digitalis purpurea is a true biennial for most cultivars, requiring a vernalization period (exposure to cold) to initiate flowering. It completes its life cycle in two years: vegetative growth in the first, flowering and seeding in the second, after which the plant usually dies. It readily self-seeds, often naturalizing in gardens.
Many other Digitalis species are true perennials. Digitalis grandiflora and Digitalis parviflora (Small-flowered Foxglove) form persistent clumps that return and flower reliably each year from the same rootstock. This perennial habit makes them more predictable and long-lived fixtures in a garden border compared to the more transient, self-sowing nature of the Common Foxglove.
