About

Digitalis purpurea, the foxglove or common foxglove, is a toxic species of flowering plant in the plantain family Plantaginaceae, native to and widespread throughout most of temperate Europe. It has also naturalized in parts of North America, as well as some other temperate regions. The plant is a popular garden subject, with many cultivars available. It is the original source of the heart medicine digoxin (also called digitalis or digitalin). This biennial plant grows as a rosette of leaves in the first year after sowing, before flowering and then dying in the second year (i.e., it is monocarpic). It generally produces enough seeds so that new plants will continue to grow in a garden setting.

How to grow it

The plant is a popular ornamental, providing height and colour in late spring and early summer. Cultivated forms often show flowers completely surrounding the central spike, in contrast to the wild form, where the flowers only appear on one side. Numerous cultivars have been developed with a range of colours. Seeds are frequently sold as a mixture (e.g. Excelsior hybrids, in shades of white, pink and purple). Some strains are easily grown by the novice gardener, while others are more challenging. They may also be purchased as potted plants in the spring.

Digitalis purpurea is hardy down to −15 °C (5 °F) (USDA zones 4–9).

Safety

Due to the presence of the cardiac glycoside digitoxin, the leaves, flowers and seeds of this plant are all poisonous to humans and some animals and can be fatal if ingested.

The main toxins in Digitalis spp. are the two chemically similar cardiac glycosides: digitoxin and digoxin. Like other cardiac glycosides, these toxins exert their effects by inhibiting the ATPase activity of a complex of transmembrane proteins that form the sodium potassium ATPase pump, (Na+/K+-ATPase). Inhibition of the Na+/K+-ATPase in turn causes a rise not only in intracellular Na+, but also in calcium, which in turn results in increased force of myocardial muscle contractions. In other words, at precisely the right dosage, Digitalis toxin can cause the heart to beat more strongly. However, digitoxin, digoxin and several other cardiac glycosides, such as ouabain, have narrow therapeutic windows (i.e., because of their steep dose-response curves, minute increases in the dosage of these drugs can make the difference between an ineffective dose and a fatal one).

Where it grows

Digitalis purpurea grows in acidic soils, in partial sunlight to deep shade, in a range of habitats, including open woods, woodland clearings, moorland and heath margins, sea-cliffs, rocky mountain slopes and hedge banks. It is commonly found and readily colonises sites where the ground has been disturbed, such as recently cleared woodland, or where the vegetation has been burnt. It also colonises areas of land that have been disturbed by clear-felling and by construction projects, being among the first wildflowers to reappear, often in large quantities. Foxgloves are eurytopic plants, as their seeds germinate when exposed to light; for this reason, they are generally absent from shaded areas, such as within woodlands.

Other Digitalis plants

Rusty foxglove · Digitalis ×fulva · Yellow Foxglove · Straw Foxglove · Digitalis parviflora · Foxgloves