Description
A tall, herbaceous biennial bearing a basal rosette of woolly leaves and a striking spike of tubular, purple-to-white, heavily spotted flowers; highly ornamental but extremely toxic, and historically important as the original source of cardiac glycosides such as digoxin.
Morphology
Digitalis purpurea is an herbaceous biennial or short-lived perennial forming, in its first year, a dense basal rosette of ovate to oblong, simple leaves 10–35 × 5–12 cm. Leaves are spirally arranged, coarsely toothed, with a strongly reticulate venation; the upper surface is dark green and softly pubescent, while the lower surface is grey-white and tomentose, giving a woolly texture.
In the second year, the plant produces one (sometimes more) erect, unbranched or sparsely branched flowering stems 1–2 m tall. The inflorescence is a showy, terminal, elongated raceme or spike, usually one-sided in wild plants. Flowers are pendulous, tubular to campanulate, 4–5 cm long, typically purple to magenta outside with a paler interior densely marked with dark purple spots on a white background; cultivated forms may be pink, rose, yellow or white.
The calyx is 5-lobed; corolla bilabiate at the mouth. Stamens are four, didynamous; the ovary is superior. Flowering mainly occurs in early to mid-summer. Pollination is primarily by long-tongued bees, which crawl into the corolla tube.
The fruit is an ovoid to ellipsoid capsule that splits at maturity, releasing numerous minute (≈0.1–0.2 mm) brown seeds, which are light-requiring and readily colonize disturbed ground
Distinguishing Features
Tall, erect spike carrying many pendulous, thimble-shaped, purple (or white/pink) flowers, typically all on one side of the stem in wild plants.
Flowers with heavily spotted interior and broad lower lip landing platform.
Basal rosette of large, grey-green, woolly leaves with strongly reticulate venation.
Extremely toxic; all parts contain cardiac glycosides.