Digitalis purpurea, foxglove or common foxglove, is a species of flowering plant in the plantain family Plantaginaceae, in the genus Digitalis, native and widespread throughout most of temperate Europe. It is also naturalized in parts of North America and some other temperate regions. The plants are well known as the original source of the heart medicine digoxin, (also called digitalis or digitalin).
D. purpurea is an herbaceous biennial or short-lived perennial plant. The leaves are spirally arranged, simple, 10–35 cm long and 5–12 cm broad, and are covered with gray-white pubescent and glandular hairs, imparting a woolly texture. The foliage forms a tight rosette at ground level in the first year. The flowering stem develops in the second year, typically 1-2m tall, sometimes longer. The flowers are arranged in a showy, terminal, elongated cluster, and each flower is tubular and pendent. The flowers are typically purple, but some plants, especially those under cultivation, may be pink, rose, yellow, or white. The inside surface of the flower tube is heavily spotted. The flowering period is early summer, sometimes with additional flower stems developing later in the season. The fruit is a capsule which splits open at maturity to release the numerous tiny 0.1-0.2 mm seeds.
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 on sites where the ground has been disturbed, such as recently cleared woodland, or where the vegetation has been burnt. Digitalis purpurea is hardy down to −15 °C (USDA zones 4–9).
Larvae of the foxglove pug (Eupithecia pulchellata), consume the flowers of the common foxglove for food. The caterpillars of this moth crawl into the newly opening flowers, one caterpillar to a flower. It then spins a silken web over the mouth of the flower, sealing it, and then proceeds to feed on the stamens and developing seeds. When the other uninfected flowers fall off, the corolla of the infected flowers remain on the plant, and the caterpillar then pupates in the flower. Though the species is uncommon, it has been recorded in Britain, Germany, Switzerland and Austria. Other species of Lepidoptera have been recorded eating the leaves, including Mellicta athalia and Xestia ashworthii in Britain, Eurodryas aurinia in Romania, and Mellicta deione in Portugal. The plant is also frequented by bees, which climb right inside the flower tube to gain the nectar within.
Digitalis purpurea is a popular garden subject, with many cultivars available and subspecies available. D. purpurea sub purpurea is found throughout most of Europe, Mararonesia, and widely introduced to other parts of the world.
D. purpurea sub amandiana is found in northern Portugal, specifically around the Douro Basin. D. purpurea sub mauretanica is found in Morocco. D. purpurea sub toletana is found in central Spain
The plant is a popular ornamental, providing height and color 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 colors. 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. The following selections have gained the Royal Horticultural Society's Award of Garden Merit: The Camelot Series, "Camelot Cream", "Camelot Lavender", "Camelot Rose", and Camelot White", the Dalmation Series, "Dalmation Creme", "Dalmation Peach", "Dalmation White", D. mertonensis (strawberry foxglove), D. purpurea f. alba, "Martina", "Pam's Choice", "The Shirley".
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. Extracted from the leaves, this same compound, whose clinical use was pioneered by William Withering, is used as a medication for heart failure. He recognized it "reduced dropsy", increased urine flow and had a powerful effect on the heart.
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. Inhibition of the Na+/K+-ATPase in turn causes a rise not only in intracellular sodium, 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, are known to have steep dose-response curves, i.e., minute increases in the dosage of these drugs can make the difference between an ineffective dose and a fatal one. Symptoms of Digitalis poisoning include a low pulse rate, nausea, vomiting, and uncoordinated contractions of different parts of the heart, leading to cardiac arrest and finally death.
Article excerpt is from Wikipedia.org under the Creative Commons License.
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