Persicaria amplexicaulis (D. Don) Ronse Decr., Red Bistort
Account Summary
Introduced, neophyte, a very rare garden escape or discard.
14 June 1985; Northridge, R.H.; Castle Caldwell FNR.
June to August.
Growth form and introduction
This attractive and distinctive, up to 1 m tall, tufted, mat-forming, garden perennial, is a native of the Himalaya, and ranges from Afghanistan to SW China. It has a stout woody rhizome and large cordate leaves. In the wild in Britain and Ireland, the plant is found naturalised on roadsides, wayside thickets, quarries and stream banks, often in sites where garden refuse is deposited.
Red Bistort was first introduced to garden cultivation in Britain and Ireland in 1826 for its decorative deep red flower spikes. It was first recorded in the wild in Britain around 1908. In Ireland, by 1920, it was said to be naturalised on the Hillsborough demesne, Co Down (H38) (J.R. Akeroyd, in: Preston et al. 2002; Cat Alien Pl Ir).
Reproduction
Red Bistort plants develop deep purple-red, claret-coloured or white flowers borne densely packed in long, slender, cylindrical spikes up to 8 cm long on naked flowering stems. The main flowering period is in late summer, from August to October, and it continues until the first frost. While Red Bistort rarely or never sets seed here, it possesses a vigorous branched rhizome or woody rootstock which spreads aggressively to the extent that it may become an invasive weedy nuisance, especially in smaller gardens (Lousley & Kent 1981). Fragments of the plant transported in soil, or with discarded garden waste, frequently enable it to 'escape' from gardens.
Variation and taxonomic nomenclature
Like other Knotweeds, this species has been renamed several times and has been placed in other genera as Bistorta amplexicaulis (D. Don) E. Greene and Polygonum amplexicaule D. Don. Seven garden cultivars are listed in the RHS Index of Garden Plants (Griffiths 1994), varying in flower colour, habit and size (eg 'Inverleigh' is a dwarf form).
Fermanagh occurrence
In Fermanagh, Red Bistort is apparently well naturalised just to the west of the Old Castle Caldwell. The only other recorded site in the VC is amongst tipped garden refuse on the moss-covered rocky floor of the disused roadside quarry, just opposite the turning for Brookeborough village.
Irish occurrence
The New Atlas map shows this species is fairly rare or scarce in Ireland, widely but thinly scattered throughout, but having been recorded in 19 of the 40 VCs. Elsewhere in N Ireland (NI), there are one or two scattered records in each of counties Tyrone, Down and Antrim (H36, H38 & H39). At one of these sites, at least, the plant persisted for over 20 years, yet Paul Hackney (in the NI Vascular Plant Database 2002) did not consider the plant fully naturalised anywhere, presumably because it does not reproduce sexually.
British occurrence
In Britain, records are concentrated in the S & SW of England, but an attenuated, increasingly disjunct presence extends northwards, mirroring a decreasing human population. P. amplexicaulis eventually reaches a remote outlier in North Aberdeenshire (VC 93). The majority of its stations are along roadsides, or in other no-man's-land where fly-tipping of rubbish and excess garden material is all too frequent. Regrettably, dumping of garden material also occurs at the coast where relatively open conditions on sand, loose gravel and shingle are especially conducive to the plant's establishment.
The increasing frequency of records in the post-1987 period displayed in both the New Atlas and in Reynold's Cat Alien Pl Ir, strongly suggests that P. amplexicaulis is still actively spreading.
European occurrence
Apart from its occurrence in Britain and Ireland, the only other record mapped for Europe by Jalas & Suominen (1979, Map 413) is from a single site in Czechoslovakia.
Names
The genus name 'Persicaria' is from the Latin 'persicum' meaning peach, and translates as either 'peach-leaved' (Gilbert-Carter 1964), or 'peach-like' (Gledhill 1985). The Latin species epithet 'amplexicaulis' is a combination of 'amplexus' meaning 'encircling' or 'embracing' and 'caulis' meaning 'stem' referring to the leaf stalk (petiole) or leaf base partially clasping the stem, which is the case in this species. The English common name 'Red Bistort' is a recent book name that merely recognises the decorative deep red flower spikes.
Threats
None.