Pentaglottis sempervirens (L.) Tausch ex L.H. Bailey, Green Alkanet

Account Summary

Origin, introduction and possible use

This leafy, 'almost-wintergreen', bristly hairy perennial which bears rather small bright-blue, white-eyed, flowers like a 'Forget-me-not' (Myosotis spp.) on short side branches, half-hidden amongst the upper leaves during April to June, is a somewhat surprising, if not to say unworthy, garden subject (Proctor & Yeo 1973; Stace & Crawley 2015). A native of SW Europe, ranging from C Portugal to SW France (Tutin et al. 1972), P. sempervirens was first introduced to cultivation in B & I at least by the late 16th century (Harvey 1981, p. 166). Possibly – or even probably – it was valued more for dyeing purposes than as a decorative garden ornament (Grigson 1955, 1987) and, indeed, many of the herbals and older gardening books have nothing to say about its virtues and they give us no clue whatsoever as to why it was cultivated. Neither is there much evidence of its use for dyeing, except perhaps as a food colorant or artists' water colour paint (Gerard 1633).

It is often difficult to decipher old herbal writers and identify which of our modern species they are discussing. The current author (RSF) believes Gerard and Johnson in the second edition of Gerard's Herbal (1633, pp. 796-7) refer to this perennial species as 'Borago sempervirens', and they linked it to the herbal medicinal virtues of Borago officinalis (Borage). Other local Flora writers carrying out this exercise appear to have settled on different members of the Boraginaceae, eg connecting P. sempervirens with Gerard's 'Alkannet' or 'Wild Bugloss' and Anchusa species, although the four kinds of alkannet described in Gerard's herbal do not match this particular species at all.

However, it is still possible to find references drawing attention to the deeply penetrating and brittle taproot of P. sempervirens as a source of red dye (Phillips & Rix 1991a, 1, p. 73) and suggesting Green Alkanet might have been a mediaeval substitute for Alkanna tinctoria (Alkanet), which itself is a poor replacement for the small tree Lawsonia inermis, from N Africa, the source of Henna dye (Grigson 1955, 1987).

Dispersal, colonising ability and preferred habitats

An early indication of the colonising ability of P. sempervirens was shown by the fact that by 1724 it had already 'jumped the wall' and been recorded in the wild (D. Welch, in: Preston et al. 2002). The species has no obvious means of dispersal and is not mentioned in Ridley's magnificent 1930 survey The dispersal of plants throughout the World. Despite this lack, it appears perfectly capable of travelling 'beyond the garden wall' to colonise open, more or less disturbed, fully lit or preferably lightly shaded ground, on mesic, moist to damp, near-neutral, moderate to richly fertile soil (Hill et al. 1999).

Typical habitats are generally located near habitation and they include waysides, the base of walls, waste places, hedgerows and the margins of woods, scrub, rivers and streams. Some years ago, Green Alkanet invaded RSF's Belfast garden, arriving unannounced in a moderately shaded bank under mature Birch and Rowan trees. It is hardy down to around -10°C (Phillips & Rix 1991a).

Although the species carries the Latin specific epithet 'sempervirens' meaning 'evergreen', it does in fact die down completely and disappear underground in the depths of winter, re-emerging after a few months in early spring.

Flowering reproduction

Flowering occurs from March or April onwards into autumn, with crop after crop of blooms on the same plant (Hutchinson 1945, 1972). The flowers are small, bright blue with a white eye, and arranged in one-sided cymose clusters in the axils of the upper leaves. They attract bees and other insects as pollinators which work the circular 'rotate' flowers with their nectar-concealing scales in the short corolla tube rather like a revolver, having five separate nectar chambers, each of which has to be separately approached from the correct angle (Proctor & Yeo 1973). The fruit of each flower consists of four separate, shortly stalked, achenes (single-seeded dry fruits) or nutlets, which are covered with fine net-like markings (Melderis & Bangerter 1955; Clapham et al. 1962). Flowering and seed production is prolific and the species is highly competitive, so that colonisation of suitable open habitats near gardens or existing colonies is often possible. The established strategy of the plant is categorised as C/CSR, ie intermediate between outright Competitor and a more balanced mixture of Competitor-Stress-tolerant-Ruderal (Grime et al. 1988, 2007).

British and Irish occurrence

Nowadays, P. sempervirens is a widespread naturalised garden escape in lowland Britain, yet while the species is particularly widely occurring in the more densely populated areas of England and Wales, it really is frequent only in SW England and is much more local or even rare elsewhere. Until the 1960s, British Floras and flower books continued to regard the species as possibly native in SW England (Melderis & Bangerter 1955; Clapham et al. 1962). Further north, and in Scotland, the species distribution becomes much more scattered, scarce and coastal (D. Welch, in: Preston et al. 2002).

The Irish distribution of P. sempervirens is very sparse and scattered compared with the occurrence in Britain, but it again reflects the areas of greatest human population density in the E & S of the island, around the larger cities of Belfast, Dublin and Cork (New Atlas; Cat Alien Pl Ir). Apart from its very rare occurrence in Fermanagh described below, further east in NI, P. sempervirens is a very much more common garden escape, fully naturalised in semi-shaded waysides, woodland and scrub margin habitats, but still chiefly occurring close to habitation.

However, since P. sempervirens is a perennial that seeds itself readily and prolifically, and being deep-rooted it is persistent once established, the species has the potential to become invasive, sometimes forming monoculture stands and becoming locally dominant (Stace & Crawley 2015). Despite its prolific level of seed production, the features that may be restricting its colonising ability are the limited means of seed dispersal, together with the lack of any obvious means of vegetative increase and secondary spread.

In Britain, accounts in a few local Floras indicate P. sempervirens is no longer confined to disturbed habitats near habitation but, instead, appears to have become more actively invasive since the 1960s, colonising a wide variety of lightly shaded sites in woodland, scrub and along rivers (Swan 1993; D. Welsh, in: Preston et al. 2002; Crawley 2005). The change in the British flora 1987-2004 survey found a marked increase in the species presence over the relevant period, a relative change of ±10%. This level of rapid increase is rather surprising, considering the length of time the species has been present in the wild in the country (Braithwaite et al. 2006).

An alternative explanation for the current distribution is that Green Alkanet quickly becomes a difficult weed to manage in garden settings and then is dug out and discarded with other fly-tipped garden outcasts around village margins, in addition to self-sown individuals on roadside banks and untended waste ground. In London, P. sempervirens is now the ninth most frequent alien found growing on walls (Stace & Crawley 2015).

Fermanagh occurrence

In Fermanagh, an extensive colony of Green Alkanet was first discovered in 1999 near Old Crom Castle under trees above the southern estate boundary and on disturbed ground below this old castle wall. It has persisted there for at least eleven years. One theory as to its occurrence at this site assumes that, like its relative Cynoglossum officinale (Hound's-tongue), P. sempervirens might possess prolonged seed longevity and therefore persist many years dormant in the soil (Roberts & Boddrell 1984). However, there does not seem to be any published evidence of seed longevity in this species (eg there is no mention in the survey of species in NW Europe (Thompson et al. 1997)).

Alternatively, the plant might have survived overlooked in what is neglected ground for a long time before coming to someone's attention. Repair work had just been completed on the wall when the plant was first noticed and it is very possible that the soil seed bank may have been disturbed during this work, resulting in germination and the reappearance of the plant. It is also feasible that the workers might have inadvertently introduced fresh seed on their tools or attached to their clothing.

The second, and so far only other appearance of the species in the VC, at Durraghstown, SW of Ballyreagh, SE of Enniskillen in April 2000, was also discovered by RHN. The dates of the two records suggests that P. sempervirens is just beginning to 'jump the wall', spread and establish itself in Fermanagh, in the unknown dispersal manner it employs elsewhere.

European and world occurrence

While its native range on the continent is rather restricted, stretching only from C Portugal to W & SW France (Grigson 1955, 1987; Phillips & Rix 1991a), P. sempervirens is widely cultivated and is naturalised in NW Europe, N Italy and N America (Tutin et al. 1972).

Names

The genus name 'Pentaglottis' is derived from two Greek words, 'pente' and 'glotta', meaning 'five tongues', a reference to the number of scales in the throat (or tube) of the corolla. The Latin specific epithet 'sempervirens' translates as 'evergreen' (Stearn 1992) although, as mentioned above, this is inaccurate. The English common name 'Alkanet' is the diminutive of the Spanish 'alcanna', which in turn is derived from the Arabic 'al-henna', the Henna tree referred to above. The 'Little Alkanna' or 'Alkanet' was the name applied to the dye plant Alkanna tinctoria, the red roots of which were long imported from the continent for many dying purposes, including colouring the red liquid in cheap thermometers! Green Alkanet, probably was a substitute for the former (Grigson 1955, 1987). An alternative English common name from Somerset is 'Pheasant's Eye', which Britten & Holland (1886) also dismissively list as, "a book name for Adonis autumnalis". The reference to the bright red eye of the bird is presumably linked to the red dyeing properties of the plant.

Threats

Currently much too rare to be considered a threat in Fermanagh, but P. sempervirens is potentially invasive whenever it becomes thoroughly established at an unknown threshold number of sites. Existing populations therefore need to be kept under review.

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