Digitalis purpurea
Written by Marissa Gidall (Lincoln University)
July 2005
Edited by Michael Hudson, Lincoln University, May 2006
Taxonomy
- Scientific name: Digitalis purpurea
- Popular Common names: Common Foxglove, Foxglove, Purple Foxglove.
- Other common names: Fairy Fingers, Jigitan sui (Japan).
- Kingdom: Plantae
- Phylum: Magnoliophyta
- Class: Magnoliopsida
- Order: Scrophulariales
- Family: Scrophulariaceae
- New Zealand Status: naturalised
- Taxonomy sources: Barnes (1998), Qualtrocchi (2000), Webb et al. (1988).
Identification
Species Description
The foxglove (Digitalis purpurea)with its distinctive long purple flowering spikes is perhaps one of the more recognizable exotic species that has escaped from the cultivated garden environment to naturalise in New Zealand. The foxglove has a basal rosette of generally dark green, rough, hairy, ovate to ovate-lanceolate leaves that are 10–25cm long. This rosette of leaves gives rise to densely hairy simple stems that grow up to 1.5 metres high. These spikes hold a one-sided array of tubular flowers, usually purple in colour although pink and white are sometimes seen. These tubular flowers are inflated, 2-lipped and bell-shaped, up to 6cm long and spotted maroon to purple on the inside (Webb et al, 1988; Bryant, 1997; Bricknell, 2003; Connor, 1977). The genus name Digitalis is derived from the Latin word Digitabulum meaning thimble or finger which these characteristic flowers resemble (Qualtrocchi, 2000).
Similar species
The genus Digitalis consists of about 22 species of biennials and short-lived perennials. Many of these species have similar growth and flower characteristics but the noticeable purple flower colour of D. purpurea distinguishes this species. Hybrids and many seedling strains of D. purpurea also exist to confuse budding botanists. A white flowering form albiflora, is common as well as a bedding annual of mixed colours called Excelsior Group. The young long basal leaves of the foxglove can also be confused with Comfrey (Symphytum officinale), of which they closely resemble. Foxgloves can be distinguished as the smaller veins in the leaves extend into the wings of the leaf-stalk. Comfrey leaves are also more lanceolate (Bryant, 1997; Bricknell, 2003; Connor, 1977).
Geographic Distribution
Full natural and naturalised range
The species D. purpurea is indigenous to continental Europe and Britain, its range having extended into the sub-continental regions over the last decade (Bruelheide & Heinemeyer 2002; Willis, Memmott & Forrester, 2000). The foxglove has naturalised in many parts of the world because of its popularity as a garden ornamental including Australia, New Zealand and North America (Willis, Memmott & Forrester, 2000).
New Zealand naturalised range
The foxglove was first recorded in New Zealand by “Kirk.T in Hooker, J.D ‘Handbook of the New Zealand Flora’ p. 761 (1867)” (Sykes, 1981, p.54). Foxgloves have a wide naturalised distribution across New Zealand inhabiting the North, South, Stewart and Campbell Islands (Sykes, 1981). In the summer months many city gardens come alive with the tall flowering spikes of the foxglove as it is still commonly cultivated by gardeners (personal observation).
Canterbury naturalised range
The foxglove has thrived in Canterbury gardens and can also be seen naturalised in parts of the region. In the months of October to January the flower spikes can be seen populating disturbed and unmanaged ground from the Canterbury east coast across the plains to the Southern Alps and the West Coast (personal observation).
Natural History in Canterbury
Habitats
The natural habitat of the foxglove is that of its wildflower status and not as a garden ornamental. It is prolific in disturbed open ground and unmanaged habitats throughout its natural range in Europe and Great Britain, and its naturalised ranges including New Zealand (Webb et al., 1988; Cameron et al., 1989). These habitats include poor pastures, scrub and forest margins, stony river beds, roadsides and tracksides. The foxglove is one of the most common naturalised species in the wetter parts of New Zealand and is abundant in the West Coast areas of the South Island where it grows up to 1000 metres above sea level (Webb et al., 1988).
Preferred habitats
The foxglove thrives in humus-rich soil in partial shade; it can however grow in almost any soil except that which is very wet or very dry. The species requires very little soil to survive contributing to its success as an exotic invader (Bricknell, 2003). The foxgloves love of damaged, disturbed ground meant that numbers in New Zealand rose significantly after it first naturalised. From its first recording in the 1860s to 1890 the numbers had risen so substantially that foxgloves completely covered many hillsides newly cleared of bush by fire (Cameron et al., 1989).
Phenology / Breeding
Foxgloves flower in early summer; in New Zealand the months of December through to February. After flowering in February numerous seeds are borne from 10–15mm long ovoid capsules on the flower stems (Webb et al., 1988; Wilson, 1996). The success of foxglove as a naturalised plant is partly down to its high seed production and ability to self-seed profusely. The high level of seed production in New Zealand foxgloves when compared with that of other naturalised species can be seen in Table 1. This advanced level of seed production in naturalised plants is associated with the seeds ability to remain dormant in the soil for significantly long periods of time (Knox, 1969). When sowing seed in cultivation they should be sown in late spring to generate the leafy rosette (Bricknell, 2003).
| Naturalised Species | Maximum Seed Output of Individual Species |
|---|---|
| Junus effuses | 2,000,000 |
| Orobanche minor | 150,000 |
| Digitalis purpurea | 93,000 |
| Hypericum perforatum | 34,000 |
| Stellaria media | 2,700 |
| Vinca augustafolia | 100 |
Longevity
As the Foxglove is a biennial or short-lived perennial plant, its first year’s growth forms the rosette of dark-green to white-woolly leaves. The second year of growth gives rise to the flower stem and the thimble-like purple flowers before seed is scattered for the next generation and the shoots die down (Bruelheide & Heinemeyer, 2002). In response to favorable conditions plants can survive for an additional one or two years after flowering. Likewise, in unfavorable conditions plants may respond by remaining in the rosette form for two to three years before flowering (Bruelheide & Heinemeyer, 2002).
Dispersal
The seeds of the foxglove are patterned and oblong. Grime et al., (1988, cited in Bruelheide & Heinemeyer, 2002, p.476) established that the seeds of the foxglove are very light, 0.07mg, and are dispersed by wind accordingly. Bruelheide and Heinemeyer (2002) explored this in seed scatter experiments and found that the dispersal distances exceeded 5.5 m when wind velocity was greater than 3.9 m s–1 at a dispersal height of 1.5 m or greater than 7.5 m s–1 at 1.0 m.
Predators and parasites
The foxglove has few predators if any at all. Animals will rarely browse on the plant instinctively reacting to its poisonous character. A small number of livestock deaths as a result of foxglove browsing have been reported in other parts of the world and very few in New Zealand (Connor, 1977). As a garden cultivar the foxglove is susceptible to leaf spot and powdery mildew (Bricknell, 2003).
In New Zealand, a biological control programme began on the naturalised species of foxglove in 1927 in response to the perceived threat to pasture. The lavae of the heath fritillary butterfly, Mellicta athalia, was imported from England and a colony of 575 trialed on foxgloves. The fate of this colony is not known, nor is it likely that any were released (DSIR files) (Connor, 1977). Two other foxglove predating insects, Eupithecia pulchellata Stephens and E. pyreneata Mabille, were imported from England in 1928. The fate of these insects is also unknown, presumably not released from observation in quarantine (Connor, 1977).
Mutualisms
Pollination of the foxglove during the flowering period can be associated with the bumble-bee (Bombus sp.) (James & Clapham,1935). In summer the long flowering stems seem to hum as the bees bury deep into the tubular flowers to get to the stamens (personal observation). Going from flower to flower the bumble-bee spreads the pollen from the stamens and hence fertilizers the flowers so productive seed is able to be produced (James & Clapham, 1935). There is mutual benefit in this relationship with the bumble-bee receiving a stable supply of nectar and the foxglove being pollinated; ensuring a secure future food source for the bumble-bee.
How to find a FOXGLOVE
Foxgloves are easier to find in Christchurch in the summer months with their tall distinctive purple flowering stems. They are abundant as garden ornamentals and easily seen poking their flower stems over people’s fences during the summer months (personal observation). Foxgloves will also be often seen naturalized in the region in the disturbed ground of stony riverbeds, scrub, forest margins, roadsides and tracksides.
Abundance and Conservation Status
- New Zealand: abundant
- Canterbury: abundant
Foxgloves are widespread throughout all of New Zealand, including Canterbury, Stewart Island and Campbell Island (Webb et al., 1988). The species has progressed from being a garden ornamental through to becoming naturalised where it forms self-sustaining populations. Concern over the effects that foxgloves may have had on the establishment of pastoral land saw that it was declared a noxious weed in 1908. However over time it was found that foxgloves cannot survive in a competitive pasture habitat and its weed status declined in importance as New Zealand's crop and farming practices improved. Today as it only inhabits disturbed, damaged land the foxglove is no longer classed as a significant danger and therefore is not noted on the noxious weed list (Cameron et al., 1989).
Significance for people
Historical Uses
The foxglove is a poisonous plant. It has throughout time been the cause of occasional poisoning in people with 3 confirmed in Christchurch (Connor, 1977). Foxglove soup has even featured as the murder weapon in an Agatha Cristie novel (Rooney, 1980). The foxgloves toxicity was officially recognized to be of benefit to people by William Withering, a prominent British physician in 1775. Withering noticed that a patient thought to be incurable recovered from dropsy after being administered an infusion of various plant parts that included the leaves of the purple foxglove. Withering then experimented with a non-lethal dose of dried powered foxglove leaves which eventually led to widespread use of Digitalis. This medical breakthrough by Withering has evolved into one of the most important modern treatments for people with heart conditions (Simpson & Conner-Orgrzaly, 1986).
Modern Uses
Today, as well as a striking garden ornamental the foxglove is important pharmacologically. The chemicals isolated proved to be steroids, primarily a type known as cardiac glycosides which have a strong effect on the heart muscles by changing the rhythm of the heart beat. Used medically they can also improve general circulation, relieve edema (dropsy) associated with heart failure and help renal secretion. The major cardiac glycosides isolated from foxgloves are Digitoxin, Gitoxin and Gitaloxin ((Simpson & Conner-Orgrzaly, 1986).
Summary
The foxglove plays an important economic role for people. From its medicinal properties through to its eye catching flowering stems providing beauty and nectar to the bumble bee, the foxglove has many facets that endear it to people. Thankfully, although it is an abundant naturalised plant it is not seen as sufficiently invasive to be detrimental to the New Zealand habitats.
References
Adams, N. (1980) Wildflowers in New Zealand. Reed, Wellington, N.Z
Barnes, R.S.K., (Ed.). (1998) The diversity of living organisms. Blackwell Sciences, Oxford, England.
Bricknell, C., (Ed.). (2003) The royal horticultural society A-Z encyclopedia of garden plant., Dorling Kindersley, London, England.
Bruelheide, H., Heinemeyer, H., (2002) Climatic factors controlling the eastern and altitudinal distribution boundary of Digitalis purpurea L. in Germany. Flora 197, 475–490
Bryant, G., (Ed.) (1997) Botanica : the illustrated A-Z of over 10,000 garden plants in New Zealand and how to cultivate them, Bateman, North Shore City, N.Z
Cameron, P.J., Hill, R.L., Bain, J., Thomas, W.P., (1989) A review of biological control of invertebrate pests and weeds in New Zealand 1874 to 1987. CAB International Institute of Biological Control, Wallingford, England; DSIR Entomology Division, Auckland, N.Z Connor, H.E., (1977) The poisonous plants in New Zealand. Botany Division, D.S.I.R, Christchurch, NZ.
Hickey, M., King, C., (1988) 100 families of flowering plants. Cambridge University Press, Cambridge, England.
James, W.O., (1935) Biology of Flowers. Clarendon Press, Oxford, England Knox, G.A, (1969) The natural history of Canterbury. Reed, Wellington, N.Z.
Pammel, L.H., (1992) A manual of poisonous plants : chiefly of eastern north America : with brief notes on economic and medicinal plants. Forestburgh, N.Y. : Lubrecht & Cramer ; Dehradun, India : Bishen Singh Mahendra Pal Singh
Qualtrocchi, U., (2000) CRC world dictionary of plant names. CRC Press, New York, USA
Rooney, D. (1980, April 11) Please don’t eat the daisies – and much more in the garden. The Press, p.13
Simpson, B.B., Conner-Orgrzaly, M., (1986) Economic botany – plants in our world, McGraw Hill Inc, Auckland, N.Z.
Sykes, W.R., (1981) Checklist of Dicotyledons naturalised in New Zealand, 7. Scrophulariales, New Zealand Journal of Botany 19, 53–57
Webb, C.J., Sykes, W.R., Garnock-Jones, P.J., (1988) Flora of New Zealand : Naturalised pteridophytes, gymnosperms, dicotyledons. Botany Division, D.S.I.R, Christchurch, N.Z
Willams, G.R., (1973) The natural history of New Zealand : an ecological survey. Reed, Wellington, N.Z.
Willis, A. J., Memmott, J., Forrester, R.I., (2000) Is there evidence for the post invasion evolution of increased size among invasive plant species? Ecology Letters 3, 275–283
Search for Digitalis purpurea in New Zealand science online
New Zealand Journal of Ecology articles containing Digitalis purpurea.
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