Digitalis purpurea

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Digitalis purpurea
Digitalis purpurea LC0101.jpg
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Asterids
Order: Lamiales
Family: Plantaginaceae
Genus: Digitalis
Species:
D. purpurea
Binomial name
Digitalis purpurea
L.

Digitalis purpurea, the foxglove or common foxglove, is a toxic species of flowering plant in the plantain family Plantaginaceae, [2] native to and widespread throughout most of temperate Europe. [3] 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.

Contents

Description

Digitalis purpurea is an herbaceous biennial or short-lived perennial plant. The leaves are spirally arranged, simple, 10–35 cm (3.9–13.8 in) long and 5–12 cm (2–5 in) 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 1–2 m (3.3–6.6 ft) 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 plant is frequented by bees, which climb right inside the flower tube to gain the nectar within.

The fruit is a capsule which splits open at maturity to release the numerous tiny 0.1-0.2 mm seeds.

Distribution

Native range

Digitalis purpurea has a native range that spans across several countries in Western Europe and North Africa. [4] In Western Europe, it is native to Belgium, Czech Republic, France, Germany, Ireland, Portugal, Spain, Sweden and the United Kingdom. In North Africa the species can be found in Morocco. Additionally, it occurs naturally on the islands of Corsica and Sardinia. [5]

Introduced range

Digitalis purpurea has been introduced throughout the world into countries and continents outside of its natural range. Due to introductions, the species has expanded its range further into Europe and Africa, as well as colonizing continents outside of the natural range, including Asia, North America, South America, and Oceania. [5]

Digitalis purpurea has been introduced extensively throughout Europe, including Austria, the Baltic States, Belarus, Denmark, Hungary, the Netherlands, Poland, Réunion, and Ukraine. It has also found its way to the Azores, the Canary Islands, Central European Russia, Madeira, and the Sakhalin and Kuril Islands.

In North America, it has been introduced into more than twenty states of the United States: Arkansas, California, Connecticut, Idaho, Maine, Maryland, Massachusetts, Michigan, Montana, New Hampshire, New Jersey, New York, North Carolina, Ohio, Oregon, Pennsylvania, Vermont, Washington, West Virginia, Wisconsin, and Wyoming. In Canada, it has colonized multiple provinces, including British Columbia, New Brunswick, Newfoundland, Nova Scotia, Ontario, and Québec. [5]

In South America, Digitalis purpurea has been introduced into Argentina, specifically in the regions of Northeast, Northwest, and South. It also can be found in Bolivia, Brazil (specifically the South and Southeast regions), Chile (Central region), Colombia, Costa Rica, Cuba, Ecuador, El Salvador, Guatemala, Jamaica, Mexico (Central, Gulf, Northeast, Southeast, and Southwest regions), Peru, Uruguay, and Venezuela. [5]

Digitalis purpurea has made its way to various regions of Asia, including China (specifically the South-Central and Southeast regions), Korea, and Vietnam. In Africa, it can be found in Malawi and Zimbabwe. Furthermore, it has been introduced to the island nations of New Zealand, both the North and South Islands. [5] It is also an established weed across multiple locations in Tasmania, Australia.

Subspecies and hybrids

A single flower of Digitalis purpurea Digitalis purpurea - flower view01.jpg
A single flower of Digitalis purpurea

Digitalis purpurea subsp. mariana is a synonym for D. mariana subsp. mariana, [11] and D. purpurea subsp. heywoodii is a synonym for D. mariana subsp. heywoodii. [11] [12]

D. dubia, a name used for populations of foxglove growing among calciferous rocks on shady cliff faces on the island of Majorca, [13] is now considered a synonym of D. minor, [14] but until recently it had been either considered to be a valid species (i.e. in the Flora Europaea (1976), [15] and the Euro+Med Plantbase (2011)), [16] as well as classified as D. purpurea subsp. dubia in 1922, [17] or Digitalis purpurea f. dubia by Spanish taxonomists in 1983. [18]

Ecology

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. [19] [20] 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. [21] 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. [22] 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. [23]

D. purpurea is most successful in humus-rich soil, but it can succeed in any soil that isn't too wet nor too dry; either way, the common foxglove only needs a small amount of soil for survival. [24]

Larvae of the foxglove pug ( Eupithecia pulchellata ), a moth, consume the flowers of the common foxglove for food. [25] 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. [26] [27] The species is uncommon, it has been recorded in Britain, [25] [27] Germany, Switzerland and Austria. [26] 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. [25]

Genetics

The four possible phenotypes for Digitalis purpurea Digitalis purpurea phenotypes.png
The four possible phenotypes for Digitalis purpurea

The colours of the petals of the Digitalis purpurea are known to be determined by at least three genes that interact with each other. [28]

The M gene determines the production of a purple pigment, a type of anthocyanin. The m gene does not produce this pigment. The D gene is an enhancer of the M gene, and leads it to produce a large amount of the pigment. The d gene does not enhance the M gene, and only a small amount of pigment is produced. Lastly, the W gene causes the pigment be deposited only in some spots, while the w gene allows the pigment to be spread all over the flower.

This combination leads to four phenotypes:

Cultivation

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). [29]

Award of garden merit

The following selections have gained the Royal Horticultural Society's Award of Garden Merit:

  • Camelot Series:
    • 'Camelot Cream' [30]
    • 'Camelot Lavender' [31]
    • 'Camelot Rose' [32]
    • 'Camelot White' [33]
  • Dalmatian Series:
    • 'Dalmatian Crème' [34]
    • 'Dalmatian Peach' [35]
    • 'Dalmatian Purple' [36]
    • 'Dalmatian White' [37]
  • D. purpurea f. alba [38]
  • 'Martina' [39]
  • 'Pam's Choice' [40]
  • 'The Shirley' (Gloxinioides group) [41]

Digitalis × mertonensis (the strawberry foxglove) [42]

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 ingested. [43]

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.[ citation needed ] 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. [43]

Medicinal use

Extracted from the leaves, this same cardiac glycoside digitoxin is used as a medication for heart failure. Its clinical use was pioneered by William Withering, who recognized it "reduced dropsy", increased urine flow, and had a powerful effect on the heart. [44] During World War II, County Herb Committees were established to collect medicinal herbs when German blockades created shortages; this included Digitalis purpurea which was used to regulate heartbeat. [45]

See also

Related Research Articles

<span class="mw-page-title-main">Cardiac glycoside</span> Class of organic compounds

Cardiac glycosides are a class of organic compounds that increase the output force of the heart and decrease its rate of contractions by inhibiting the cellular sodium-potassium ATPase pump. Their beneficial medical uses include treatments for congestive heart failure and cardiac arrhythmias; however, their relative toxicity prevents them from being widely used. Most commonly found as secondary metabolites in several plants such as foxglove plants and milkweed plants, these compounds nevertheless have a diverse range of biochemical effects regarding cardiac cell function and have also been suggested for use in cancer treatment.

<i>Digitalis</i> Genus of flowering plants in the family Plantaginaceae

Digitalis is a genus of about 20 species of herbaceous perennial plants, shrubs, and biennials, commonly called foxgloves.

<span class="mw-page-title-main">Digitoxin</span> Chemical compound

Digitoxin is a cardiac glycoside used for the treatment of heart failure and certain kinds of heart arrhythmia. It is a phytosteroid and is similar in structure and effects to digoxin, though the effects are longer-lasting. Unlike digoxin, which is eliminated from the body via the kidneys, it is eliminated via the liver, and so can be used in patients with poor or erratic kidney function. While several controlled trials have shown digoxin to be effective in a proportion of patients treated for heart failure, the evidence base for digitoxin is not as strong, although it is presumed to be similarly effective.

<span class="mw-page-title-main">Phytochemistry</span> Study of phytochemicals, which are chemicals derived from plants

Phytochemistry is the study of phytochemicals, which are chemicals derived from plants. Phytochemists strive to describe the structures of the large number of secondary metabolites found in plants, the functions of these compounds in human and plant biology, and the biosynthesis of these compounds. Plants synthesize phytochemicals for many reasons, including to protect themselves against insect attacks and plant diseases. The compounds found in plants are of many kinds, but most can be grouped into four major biosynthetic classes: alkaloids, phenylpropanoids, polyketides, and terpenoids.

<i>Molinia caerulea</i> Species of grass

Molinia caerulea, known by the common name purple moor-grass, is a species of grass that is native to Europe, west Asia, and north Africa. It grows in locations from the lowlands up to 2,300 m (7,546 ft) in the Alps. Like most grasses, it grows best in acid soils, ideally pH values of between 3.5 and 5, however, it can continue to live under more extreme conditions, sometimes to as low as 2. It is common on moist heathland, bogs and moorland throughout Britain and Ireland. Introduced populations exist in northeastern and northwestern North America.

<i>Sarracenia purpurea</i> Species of carnivorous plant

Sarracenia purpurea, the purple pitcher plant, northern pitcher plant, turtle socks, or side-saddle flower, is a carnivorous plant in the family Sarraceniaceae.

<i>Sambucus nigra</i> Species of flowering plant in the moschatel family Adoxaceae

Sambucus nigra is a species complex of flowering plants in the family Adoxaceae native to most of Europe. Common names include elder, elderberry, black elder, European elder, European elderberry, and European black elderberry. It grows in a variety of conditions including both wet and dry fertile soils, primarily in sunny locations. The plant is widely grown as an ornamental shrub or small tree. Both the flowers and the berries have a long tradition of culinary use, primarily for cordial and wine.

<i>Digitalis lanata</i> Species of flowering plant in the plantain family Plantaginaceae

Digitalis lanata, vernacularly often called woolly foxglove or Grecian foxglove, is a species of foxglove, a flowering plant in the plantain family Plantaginaceae. It gets its name due to the woolly indumentum of the leaves. D. lanata, like other foxglove species, is toxic in all parts of the plant. Symptoms of digitalis poisoning include nausea, vomiting, severe headache, dilated pupils, problems with eyesight, and convulsions at the worst level of toxicity. The plant is also harmful to other animals.

<i>Digitalis grandiflora</i> Species of foxglove

Digitalis grandiflora, the yellow foxglove, big-flowered foxglove, or large yellow foxglove, is a species of flowering plant in the genus Digitalis, family Plantaginaceae. It is native to southern Europe and Asia. In mountains it grows on warm, bushy slopes or areas left after logging. The Latin specific epithet grandiflora means “large flowered”.

<i>Penstemon digitalis</i> Eastern North American species of penstemon

Penstemon digitalis is a species of flowering plant in the plantain family, Plantaginaceae. The flowers are white and are borne in summer. It is native to eastern Canada and the eastern and southeastern United States. Penstemon digitalis is the most widespread species of Penstemon east of the Mississippi River.

<i>Trillium albidum</i> Species of flowering plant

Trillium albidum is a species of flowering plant in the bunchflower family Melanthiaceae. It is the only trillium characterized by a stalkless white flower. The species is endemic to the western United States, ranging from central California through Oregon to southwestern Washington. In the San Francisco Bay Area, it is often confused with a white-flowered form of Trillium chloropetalum. In northern Oregon and southwestern Washington, it has a smaller, less conspicuous flower.

<i>Digitalis ferruginea</i> Species of flowering plant in the family Plantaginaceae

Digitalis ferruginea, the rusty foxglove, is a species of flowering plant in the family Plantaginaceae, native to Hungary, Romania, Turkey and the Caucasus. It is a biennial or short-lived perennial plant growing to 1.2 m, which forms a rosette of oblong dark green leaves and carries spikes of brown, tubular flowers in summer.

<i>Digitalis thapsi</i> Species of foxglove

Digitalis thapsi, which has been called mullein foxglove in the US, is a flowering plant in the genus Digitalis that is endemic to the Iberian Peninsula, where it occurs in eastern Portugal and central and western Spain. It is of commercial importance as an ornamental plant. Hybrids with D. purpurea have proved successful and are fertile.

<i>Digitalis <span style="font-style:normal;">×</span> fulva</i> Hybrid species of flowering plant

Digitalis × fulva, the strawberry foxglove, is a hybrid species of flowering plant within the family Plantaginaceae. It is a naturally occurring fertile hybrid between the species Digitalis grandiflora and Digitalis purpurea. The species is widely marketed in the UK under the common name strawberry foxglove or its taxonomic synonym Digitalis × mertonensis. The species has been used to produce various cultivars and has gained the Royal Horticultural Society's Award of Garden Merit.

<i>Digitalis ciliata</i> Species of plant

Digitalis ciliata, commonly called hairy foxglove is a member of the genus Digitalis. It has thimble-shaped, yellow to cream colored flowers produced on perennial plants with evergreen foliage. It is native to the Caucasus and is grown as an ornamental in other parts of the world. The species name is derived from the fine hairs that cover the plants stems and flowers.

<i>Digitalis obscura</i> Species of plant

Digitalis obscura, commonly called willow-leaved foxglove or dusty foxglove or spanish rusty foxglove, is a flowering plant native to regions in Spain and Morocco. It is also grown as an ornamental flower. This foxglove is a woody perennial plant belonging to the family Plantaginaceae. Along with the other foxgloves it used to be placed in the figwort family, Scrophulariaceae; however, recent genetic research has moved the genus Digitalis to a larger family. It is similar to many of the foxglove species in its high toxicity and medicinal use as a source for the heart-regulating drug digoxin. Its strikingly distinctive amber- to copper-coloured flowers give the species its name and help distinguish it from other members of the genus.

<i>Digitalis davisiana</i> Species of foxglove

Digitalis davisiana is a species of foxglove, a herbaceous plant in the genus Digitalis in the family Plantaginaceae, formerly in the Scrophulariaceae and briefly the Veronicaceae. It is native to Turkey.

<i>Digitalis parviflora</i> Species of foxglove

Digitalis parviflora, the small-flowered foxglove, is a species of flowering plant in the plantain family Plantaginaceae. It is endemic to northern and central Spain. It grows at 500–2000 metres in altitude.

<i>Digitalis mariana</i> Flowering plant in the family Plantaginaceae

Digitalis mariana is a flowering plant species in the family Plantaginaceae. It is a perennial foxglove with evergreen foliage and rose-red coloured flowers produced in summer. It is native to Portugal and Spain.

<i>Digitalis minor</i> Species of plant

Digitalis minor is a species of flowering plant in family Plantaginaceae, which has been called dwarf Spanish foxglove. It is a biennial or short-lived perennial species of foxglove which is endemic to the Balearic islands with large, pendulous, pink or purple flowers. Closely related to the common purple foxglove, it is best distinguished by its small fruits. It is one of the only foxgloves to grow in calciferous, alkaline soils.

References

  1. ↑ Chadburn, H. (2014). "Digitalis purpurea". IUCN Red List of Threatened Species . 2014: e.T203383A2764797. Retrieved 4 June 2021.
  2. ↑ Olmstead, R. G.; dePamphilis, C. W.; Wolfe, A. D.; Young, N. D.; Elisons, W. J. & Reeves P. A. (2001). "Disintegration of the Scrophulariaceae". American Journal of Botany. 88 (2): 348–361. doi: 10.2307/2657024 . JSTOR   2657024. PMID   11222255.
  3. ↑ "Digitalis purpurea - Plant Finder". www.missouribotanicalgarden.org. Retrieved 2021-02-22.
  4. ↑ Rana, Sonali & Singh, Suneeta & Bisht, Anand. (2022). DIGITALIS PURPUREA L: AN OVERVIEW ON IMPORTANT MEDICINAL PLANT.
  5. 1 2 3 4 5 "Digitalis mariana Boiss". Plants of the World Online . Royal Botanic Gardens, Kew. 2017. Retrieved 22 November 2020.
  6. ↑ "Infraspecific Taxon Details : Digitalis purpurea subsp. purpurea". Catalogue of Life . Retrieved 21 November 2020.
  7. ↑ "Infraspecific Taxon Details : Digitalis purpurea subsp. amandiana (Samp.) P. A. Hinz". Catalogue of Life . Retrieved 21 November 2020.
  8. ↑ "Digitalis purpurea subsp. amandiana (Samp.) P.A.Hinz". flora.on. Retrieved 21 November 2020.
  9. ↑ "Infraspecific Taxon Details : Digitalis purpurea subsp. mauretanica (Humbert & Maire) A. M. Romo". Catalogue of Life . Retrieved 21 November 2020.
  10. ↑ "Infraspecific Taxon Details : Digitalis purpurea subsp. toletana (Font Quer) P. A. Hinz". Catalogue of Life . Retrieved 21 November 2020.
  11. 1 2 "Digitalis mariana Boiss". Plants of the World Online . Royal Botanic Gardens, Kew. 2017. Retrieved 22 November 2020.
  12. ↑ "Infraspecific Taxon Details : Digitalis purpurea subsp. heywoodii P. & M. Silva". Catalogue of Life . Retrieved 21 November 2020.
  13. ↑ Davis, Peter H. (March 1951). "Cliff Vegetation in the Eastern Mediterranean". Journal of Ecology. 39 (1): 83. doi:10.2307/2256628. JSTOR   2256628 . Retrieved 25 November 2020.
  14. ↑ "Digitalis minor L." Plants of the World Online . Royal Botanic Gardens, Kew. 2017. Retrieved 26 November 2020.
  15. ↑ Digitalis species list. Flora Europaea, Vol. 4 (1976)
  16. ↑ Marhold, Karol (2011). Greuter, Werner; von Raab-Straube, E. (eds.). "Details for: Digitalis dubia". Euro+Med Plantbase. Botanic Garden and Botanical Museum Berlin-Dahlem . Retrieved 25 November 2020.
  17. ↑ Benedí i Gonzalez, Carles; Hinz Alcaraz, P.-A. (15 January 2009). "17. Digitalis" (PDF). In Benedí i Gonzalez, Carles; Rico Hernández, Enrique; Güemes Heras, Jaime; Herrero Nieto, Alberto (eds.). Flora Ibérica, Vol. XIII (PDF) (in Spanish). Madrid: Real Jardín Botánico. p. 356. ISBN   9788400087470.
  18. ↑ "Digitalis purpurea f. dubia". International Plant Names Index . The Royal Botanic Gardens, Kew, Harvard University Herbaria & Libraries and Australian National Botanic Gardens. Retrieved 26 November 2020.
  19. ↑ Anon. "Foxglove (Digitalis purpurea)". Arkive: images of life on Earth. Wildscreen. Archived from the original on 13 June 2010. Retrieved 6 May 2010.
  20. ↑ Anon. "Foxglove: Digitalis purpurea (Scrophulariaceae)". Wildflowers in Bloom. Wildseed farms. Retrieved 7 May 2010.
  21. ↑ Klein, Carol (18 May 2002). "How to grow: Foxgloves". The Telegraph. London: Telegraph Media Group Limited. Retrieved 6 May 2010.
  22. ↑ "Digitalis purpurea, Foxglove: identification, distribution, habitat". www.first-nature.com. Retrieved 2024-01-21.
  23. ↑ "Gardening features from Crocus.co.uk - Bee-friendly Foxgloves". www.crocus.co.uk. Retrieved 2024-01-21.
  24. ↑ Rana, S., Singh, S., & Bisht, A. S. (2022). Digitalis pupurea L.: An overview on important medicinal plant. Advances in Agriculture For Doubling Farmers’ Income, 190-194.
  25. 1 2 3 Robinson, G. S.; Ackery, P. R.; Kitching, I. J.; Beccaloni, G. W.; Hernández, L. M. (2010). "Digitalis". HOSTS – A Database of the World's Lepidopteran Hostplants. Natural History Museum, London . Retrieved 28 November 2020.
  26. 1 2 "08484 Eupithecia pulchellata STEPHENS, 1831 - Rotfingerhut-Blütenspanner". Lepiforum (in German). Lepiforum e. V. 28 April 2018. Retrieved 28 November 2020.
  27. 1 2 Kimber, Ian. "70.151 BF1817 Foxglove Pug Eupithecia pulchellata". UKMoths. Ian Kimber. Retrieved 28 November 2020.
  28. ↑ Griffiths AJF, Miller JH, Suzuki DT, et al. An Introduction to Genetic Analysis. 7th edition. New York: W. H. Freeman; 2000. Gene interaction in petal color of foxgloves.
  29. ↑ Perennials.com: Digitalis purpurea ‘Dalmatian Purple’
  30. ↑ "Digitalis purpurea 'Camelot Cream'". RHS. Retrieved 5 May 2020.
  31. ↑ "Digitalis purpurea 'Camelot Lavender'". RHS. Retrieved 5 May 2020.
  32. ↑ "Digitalis purpurea 'Camelot Lavender'". RHS. Retrieved 5 May 2020.
  33. ↑ "Digitalis purpurea 'Camelot White'". RHS. Retrieved 5 May 2020.
  34. ↑ "Digitalis purpurea 'Dalmatian Crème'". RHS. Retrieved 5 May 2020.
  35. ↑ "Digitalis purpurea 'Dalmatian Peach'". RHS. Retrieved 5 May 2020.
  36. ↑ "Digitalis purpurea 'Dalmatian Purple'". RHS. Retrieved 22 June 2023.
  37. ↑ "Digitalis purpurea 'Dalmatian White'". RHS. Retrieved 5 May 2020.
  38. ↑ "RHS Plant Selector - Digitalis purpurea f. alba" . Retrieved 27 May 2020.
  39. ↑ "Digitalis 'Martina'". RHS. Retrieved 5 May 2020.
  40. ↑ "Digitalis purpurea 'Pam's Choice'". RHS. Retrieved 5 May 2020.
  41. ↑ "RHS Plant Selector - Digitalis purpurea 'The Shirley' (Gloxinioides group)" . Retrieved 27 May 2020.
  42. ↑ "Digitalis × mertonensis". RHS. Retrieved 5 May 2020.
  43. 1 2 "Digitalis purpurea (Common Foxglove, Foxglove) | North Carolina Extension Gardener Plant Toolbox". plants.ces.ncsu.edu. Retrieved 2021-02-22.
  44. ↑ "William Withering | English physician". Encyclopedia Britannica. Retrieved 2021-02-22.
  45. ↑ Sumner, Judith (2019). Plants Go to War: a Botanical History of World War II. Jefferson, North Carolina: McFarland. pp. 186–187. ISBN   978-1-4766-7612-8. OCLC   1049778338.

Bibliography

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