Lamium purpureum L., Red Dead-nettle

Account Summary

Growth form and preferred habitats

A common and familiar hairy, short-lived, ruderal winter- or summer-annual weed with stems branching from the base and growing up to 45 cm tall, but often closer to 10 cm in height. The opposite, petiolate leaves are frequently purple-tinged and this is especially the case with the inflorescence bracts.

L. purpureum is characteristic of a wide range of open, cultivated and disturbed soils, most commonly found in lowland areas on roadsides, waste ground, in gravel, on field margins, in garden flowerbeds and in bare soil around specimen trees and shrubs. L. purpureum is recorded throughout the year. It is most prevalent close to habitation and grows vigorously, colonises and competes best in sunny, warm sites on disturbed, relatively fertile, damp to dry, moderately acid to calcareous, loam and clay soils (Sinker et al. 1985).

Fermanagh occurrence

In Fermanagh, as the tetrad distribution map shows, L. purpureum is common and widespread in the lowlands, having been recorded in every month and from 130 tetrads, 24.6% of those in the VC.

L. purpureum can be distinguished from L. hybridum (Cut-leaved Dead-nettle), the only other red deadnettle in Fermanagh, by the leaves being more bluntly and regularly (ie evenly) toothed than the latter and by a more definite ring of hairs present on the inner surface of the corolla tube near its base.

Flowering reproduction

Although categorised as a short-lived, ruderal annual, Red Dead-nettle has a long flowering season, stretching from March to October, although the main flush occurs from April to June. In arable fields growing winter barley, L. purpureum behaves as a winter-annual, germinating in the autumn, overwintering as a very small, frost-tolerant leaf rosette, flowering early in spring and setting seed before the crop develops a dense canopy (Salisbury 1962, p. 349; Grime et al. 1988, 2007).

The terminal inflorescence on each erect stem is rather dense, but is often few flowered, containing only around 4-12 oppositely arranged flowers. The corolla is 10-15 mm long, pinkish-purple, the tube being longer than the 5-7 mm tubular-campanulate calyx. Although the bisexual, homogamous, zygomorphic, 2-lipped flowers are obviously designed for cross-pollination and they attract bees by offering nectar and pollen food, they are probably often self-pollinated (Clapham et al. 1987). Despite its often small size, individual plants frequently produce abundant nutlets, with plants quoted as producing in excess of 1,000 (Roberts & Boddrell 1983a). The seed can persist buried in soil for up to five years or more (Thompson et al. 1997).

As in L. album (White Dead-nettle), the seed has an attached nutritive oil-body or elaiosome that attracts ants that help to disperse it locally. This local dispersal is a significant means of avoiding seed predation, but it does not explain the observed widespread colonising ability of the species, which remains something of a mystery. Presumably the small seeds are dispersed by wind to some extent, although the plant is rather low-growing for this to be effective over more than a metre or so. The only other conceivable mechanisms might involve accidental transport in soil and mud attached to man and other animals (Grime et al. 1988, 2007) or, perhaps, as a commercial crop seed impurity in past times. The fact that L. purpureum has been reported as a widespread introduction in New Zealand, spreading rapidly only in the post-1940 period, does point strongly to the latter means of long-range seed dispersal (Webb et al. 1988, p. 773).

Vegetative reproduction

Very unusually for an annual species, in the cooler months of autumn and in milder weather during the winter, L. purpureum can develop a limited degree of vegetative spread prior to reaching the flowering stage. In these cool, mild weeks, the immature plant leaf rosette may occasionally produce prostrate shoots which can root at their nodes and develop a clump or patch of the plant (Salisbury 1964). It is also said that non-flowering shoot tips that become detached, eg after soil is rotavated, can re-root, re-establish the plant and eventually flower and set seed (Hodgson, unpublished, quoted in Grime et al. 1988, 2007).

Species status and British and Irish occurrence

Previously, most botanists in B & I assumed or regarded L. purpureum as native, but Webb (1985) listed it with 40 other species he suggested were doubtfully native and in need of reassessment. Interestingly, in this connection, it remains 'native' in the posthumously published 7th revision of Webb's An Irish Flora (1996). Godwin (1975) noted that while the fossil finds of L. purpureum from the current interglacial in Britain (the Flandrian) conform to the present habit of the plant, favouring cultivated ground and waste places, finds from two earlier interglacial periods (Hoxnian and Ipswichian) showed it had a capacity for existence in a countryside far less affected, if at all, by the activities of man. The editors of the New Atlas now recognise L. purpureum as an ancient introduction throughout B & I (K. Walker, in: Preston et al. 2002).

In B & I, L. purpureum is common and widespread throughout suitable disturbed lowland habitats, becoming scarce or absent only on very acid soils, wetlands and in woodland shade (Grime et al. 1988, 2007). The New Atlas hectad map data suggest there has been a decline of L. purpureum in Scotland, possibly due to the abandonment of marginal arable land (K. Walker, in: Preston et al. 2002).

European and world occurrence

L. purpureum belongs to the European temperate phytogeographic element and is widespread and common throughout most of Europe, although it becomes confined to the mountains towards the south and in the Mediterranean basin. It is also absent in all of the Mediterranean islands E of Capri, including Sicily. Hultén & Fries (1986, Map 1590) reckon L. purpureum probably originated in the east of its European range, but it has spread widely as an agricultural weed, including to N America, Greenland and Iceland and probably also to N Africa (Böcher et al. 1968; Löve 1983). It has definitely been introduced to New Zealand and from 1940 onward has become much more widespread there (Webb et al. 1988).

Medicinal uses

Red Dead-nettle has been used in herbal medicine to a very limited extent, in much the same manner as L. album (White Dead-nettle) and Galeobdalon luteum (= L. galeobdalon) (Yellow Archangel) for healing sores and ulcers. Neither of these species gets more than a passing mention by Grieve (1931) in her authoritative book, A modern herbal.

However, Allen & Hatfield (2004) report that an infusion of L. purpureum in a quart of wine has been drunk in Essex as a treatment for piles (bound to work wonders!). Elsewhere, in East Anglia, it featured as a cure for certain unnamed diseases of poultry and, in Co Meath, in Ireland, a decoction of the roots has been recommended to take out the rash in measles. In Kerry, an infusion has been drunk for headaches. Since similar uses are reported for Betony (Stachys officinalis), it may be that L. purpureum was serving as a mere stand-in for the preferred species (Allen & Hatfield 2004).

Names

The genus name 'Lamium' is from the Greek 'laminos' meaning 'throat' or 'gullet', a reference to the corolla tube (Johnson & Smith 1972; Gledhill 1985). The Latin specific epithet 'purpureum' was applied to various shades of red rather than purple (Gilbert-Carter 1964) or maybe it better referred to 'reddish-purple' (Gledhill 1985).

Vickery (2019) lists a total of 17 English common names and Grigson (1955, 1987) weights in with 16, some of which do not overlap with Vickery's. Many of the names are also applied to L. album, especially those with the word elements 'Dead' and/or 'Nettle', such as 'Deaf-nettle', 'Dumb-nettle' and 'Dunch-nettle'. It gets the name 'Bad-man's posey', 'Bad-man's posies' or 'Blackman's posies' in the N of England, the 'bad-' or 'black-' man referring to the Devil. Like other species of Dead-nettle, L. purpureum was locally referred to as 'Red archangel' in Lancashire, the 'Archangel' appellation presumably because it had the angelic quality of not stinging when touched (Grigson 1955, 1987).

Threats

None.

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