The foxgloves are familiar, usually tall and large-flowered garden ornamentals. Digitalis purpurea is especially well known as the source of a cardiac medicine, first reported in 1785 by the British botanist and physician William Withering, after a decade of research on an effective folk medicine. These are poisonous plants, the line between therapeutic and toxic doses rather narrow. Corolla color in the key refers to the general ground color, not to spots or other markings.
1. Pedicels and axis of the inflorescence glabrous; corolla ca. 1.3–2.1 cm long, white to yellowish.
1. Pedicels and axis of inflorescence densely glandular-pubescent; corolla ca. (1.9–) 2.3–5 cm long, white, yellow, or purple.
2. Corolla ca. (1.9–) 2.3–3 cm long, the lower lip with very greatly prolonged middle lobe; inflorescence densely covered with long (over 1 mm) hairs.
2. Corolla ca. (2.8–) 3.5–5 cm long, the lower lip with middle lobe scarcely longer than the lateral lobes; inflorescence (pedicels and axis) densely covered with short hairs (less than 0.5 mm).
3. Calyx lobes linear-lanceolate; corolla yellow; leaves glabrous above.
3. Calyx lobes broadly ovate; corolla purple (rarely white); leaves pubescent (rarely glabrate) above.
All species found in Digitalis
MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. December 12, 2017. http://www.michiganflora.net/genus.aspx?id=Digitalis.