Spiraea salicifolia L., Bridewort

Introduction, neophyte, a rare garden escape. Native of Eurasia, from Central Europe eastwards.

6 September 2001; Northridge, R.H.; mainland shore of Lower Lough Erne, near Portinode Bridge across to Boa Island.

June to September.

This deciduous, decorative garden shrub, up to 2 m tall, has only been very recently recorded in Fermanagh, as first listed above, but here as elsewhere in B & I it is probably more widespread than is presently realised. A fluffy, cylindrical, pink-panicled, hedging species that suckers readily, S. salicifolia is a persistent relict of cultivation or a garden discard that escapes into the wild and can become thoroughly naturalised. It tends to favour colonising rough grassland, or shaded, wet ground in or near hedgerows or on waste ground. So far in Fermanagh, it has appeared in lakeshore and riverside situations, all three Fermanagh records being post-2000 and discovered by RHN. In addition to the first record above, the other details are: Kesh, 6 September 2001; and White Bridge, Colebrooke Estate, 24 June 2003. The tentative position in Fermanagh is that this plant is very thinly scattered in the eastern half of the county in hedgerows and on waste ground on damp, rough terrain.

The true position regarding the occurrence of cultivated Spiraea species throughout B & I has yet to become clear, since until the publication of Stace's New Flora of the BI in 1991, or indeed perhaps as late as the publication of A.J. Silverside's later account in the BSBI Plant Crib (1998), there was considerable confusion in the genus. This was particularly the case between species, varieties and hybrids involving S. salicifolia and the more recently recognised S. alba Du Roi (Pale Bridewort) and S. douglasii Hook. (Steeple-bush) (Silverside 1990). All three species have an elongated terminal panicle of crowded, small flowers as their inflorescence, although care is required as the leaf shape, inflorescence shape and flower colour are all variable. S. salicifolia was the first of these species to be brought into cultivation in Europe, but to some extent it has been replaced in gardens by the two more recently introduced N American forms and by the subsequent hybrids between the species. Before 1991, the naturalised Spiraea populations were usually recorded as S. salicifolia and, consequently, it is over-recorded. Having said this, most pre-1991 records can really only be ascribed to a broad aggregate comprising all three species and their three hybrids (Stace et al. 2015).

S. salicifolia has almost hairless leaves and can be distinguished from S. × pseudosalicifolia (its hybrid with S. douglasii) which has hairy leaves and sepals bent backwards in fruit, and from S. douglasii which also has hairy leaves, but these are toothed only in the top half (Parnell & Curtis 2012). S. salicifolia has a cylindrical inflorescence of usually bright pink flowers and leaves are widest just below half way, while S. alba has a pyramidal inflorescence with distinct branches near its base and white or very pale pink flowers and its leaves are widest just above half way (Stace et al. 2015).

The native distributions of the three Spiraea species do not overlap in the wild: S. salicifolia is from Eurasia, S. alba from eastern N America and S. douglasii from western N America (Stace et al. 2015). All three species are strongly suckering and the hybrids, which must have arisen in cultivation, can produce invasive thickets on damp, peaty soils. Taxonomic uncertainties developed to the extent that at one time Silverside (1990) doubted whether or not true S. salicifolia existed in these islands at all.

This taxonomic and identification confusion is reflected in the treatment given in two books on alien species in B & I (Clement & Foster 1994; Reynolds 2002) and also in the maps and accounts published in the New Atlas. All accounts of these Spiraea forms must really be regarded as purely tentative in their statements and conclusions.