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Lamiastrum galeobdolon (L.) Ehrend. &
Polatschek subsp. argentatum
(Smejkal) Stace, a Yellow
Archangel

Account Summary

Introduced, naturalised garden escape, rare.

21 April 1996; Northridge, R.H.; naturalised on a wooded riverbank, Derryany Bridge, NE of Cargin Lough.

April and May

There are records of this recently arrived hairy, perennial garden escape or discard from 22 tetrads in Fermanagh (4.2%), typically thinly scattered near habitation. It has erect flowering stems that grow up to 60 cm tall and has broadly ovate, crenate, opposite leaves with permanent, conspicuous silvery-white blotches on all leaves. The flowers are yellow, about 2 cm across, two-lipped, and borne in whorls of more than ten per node at four nodes in leaf axils towards the top of the stem (Sell & Murrell 2009).

L. galeobdolon subsp. argentatum is thought to have been first introduced to B & I gardens sometime in the 1960s, its rapid growth and long arching stolons quickly recommending it as a useful ground cover plant for difficult habitat conditions such as dry shade. Experience soon led to a reassessment and the plant is now recognised as a rampant, aggressive and extremely invasive, creeping stoloniferous garden subject, of unknown, but probable horticultural origin. Thanks to its stolons and successful seed production, subsp. argentatum readily escaped garden confines and first appeared in the wild in Britain as recently as 1974 (Rutherford & Stirling 1987; Clement & Foster 1994; Stace & Crawley 2015). It made its first appearance in Ireland by the River Nier S of Clonmel, Co Waterford (H6) in 1987 (Cat Alien Pl Ir).

L. galeobdolon subsp. argentatum is a close relative of the Yellow Archangel, L. galeobdolon subsp. montanum (Pers.) Ehrend. & Polatschek which is a tetraploid native plant in Ireland, confined to the SE counties that lie to the south of Dublin. Subsp. argentatum is also a tetraploid and the most obvious difference it shows from variegated forms of the native plant, with which it is very easily confused, is the conspicuous whitish leaf blotches carried throughout the year, which turn brownish-maroon along the midrib and lateral veins in the wintertime (Rutherford & Stirling 1987; Ellis 1993). The floral parts of subsp. argentatum are also slightly larger than those of subsp. montanum and it appears likely that it really represents a mutation of the latter, rather than being a distinct new subspecies. The invariable isozyme characters of subsp. argentatum suggest it may even represent a single clone (Stace & Crawley 2015).

An introduced plant of subsp. argentatum in the wild, shaded in woodland or otherwise, can cover as much as 100 m2 in two years (The Times newspaper, 22 May 2001). Being such an aggressive ground-cover plant, many gardeners on obtaining first-hand experience of subsp. argentatum may quickly decide to eradicate or severely thin it in their gardens. It therefore tends to be found where garden rubbish is dumped and all too often this means on quiet wayside verges off the beaten track and in shrubberies. The widespread explosion of recent occurrences of naturalised patches of subsp. argentatum all across these islands must nearly all derive from garden thinnings thoughtlessly dumped where they can survive, establish and spread (K. Walker, in: Preston et al. 2002).

Fermanagh Occurence

Threats

An extremely invasive plant, it could become a very serious threat to natural vegetation, as has already happened in S Devon (VC 3). It should be carefully monitored, as it may need to be controlled.