Digitalis purpurea

This article is about the flowering plant. For the band, see Digitalis Purpurea (band).

Digitalis purpurea
Digitalis purpurea (Common Foxglove)
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Asterids
Order:	Lamiales
Family:	Plantaginaceae
Genus:	Digitalis
Species:	D. purpurea
Binomial name
Digitalis purpurea L.

Digitalis purpurea (Common Foxglove, Purple Foxglove or Lady's Glove), is a flowering plant in the family Plantaginaceae (formerly treated in the family Scrophulariaceae), native to most of Europe.

Description

Digitalis 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. The foliage forms a tight rosette at ground level in the first year.

The flowering stem develops in the second year, typically 1 to 2 m 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 corolla is spotted inside the bottom of the tube. 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.

Subspecies

There are three subspecies:

• Digitalis purpurea subsp. purpurea – most of Europe
• Digitalis purpurea subsp. heywoodii – Iberia
• Digitalis purpurea subsp. mariana – Iberia

Hybrids

• Digitalis x fulva, Lindl. 1821

(Hybrid formula: Digitalis grandiflora Mill. × Digitalis purpurea L.).

Toxicity

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 eaten.

Extracted from the leaves, this same compound, whose clinical use was pioneered as digitalis by William Withering, is used as a medication for heart failure. He recognized that it "reduced dropsy", increased urine flow and had a powerful effect on the heart. Unlike the purified pharmacological forms, extracts of this plant didn't frequently cause intoxication because they induced nausea and vomiting within minutes of ingestion, preventing the patient from consuming more.

The main toxins in Digitalis are the two chemically similar cardiac glycosides: digitoxin and digoxin. Like other cardiac glycosides, the Digitalis 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, 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.

Uses

The plant is sometimes grown in gardens. In suitable conditions it generally seeds itself in partial shade, and can become a minor weed. The pollen contains up to 80% digitalis and this pollen can be found on neighboring plants stamens when they are in bloom. This effect can cause accidental digitalis exposure if the exposed stamens of other plants are consumed in any way by humans. During the peak pollen production, in some areas the pollen floats heavily in the air and will stick to exposed surfaces.

Selected forms, either for colour or for dwarf habit, are sold as pot plants.

Use in Molecular Biology: Digoxigenin

Digoxigenin (DIG) is a steroid found exclusively in the flowers and leaves of the plants Digitalis purpurea and Digitalis lanata. It is used as a molecular probe to detect DNA or RNA. It can easily be attached to nucleotides by chemical modifications. DIG molecules are often linked to uridine nucleotides; DIG labeled uridine (DIG-U) can then be incorporated into RNA probes via in vitro transcription. Once hybridisation occurs in situ, RNA probes with the incorporated DIG-U can be detected with anti-DIG antibodies that are conjugated to alkaline phosphatase. To reveal the hybridised transcripts, alkaline phosphatase can be reacted with a chromogen to produce a colour precipitate.

In Literature and Music

This plant inspired a famous poem by the Italian poet Giovanni Pascoli titled "Digitale Purpurea". It also inspired the Italian industrial metal band Digitalis Purpurea.

Gallery

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  f.albiflora

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  19th century illustration

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  Flower close-up

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  Leaves

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  Young plant a few weeks old

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  Giant flower demonstrating pseudo-peloria

References

• Flora Europaea: Digitalis purpurea
• Ecological flora of the British Isles: Digitalis purpurea
• Skye Flora: Digitalis purpurea
• Purple Foxglove USDA Invasive Plants of the US