Salix cinerea × S. aurita (S. × multinervis Döll), a hybrid willow

Account Summary

Fermanagh occurrence

This hybrid was described by Meikle (1984) as very common, found everywhere the parent species occur. If this really is the case, it is distinctly odd that it was not noted in Fermanagh by anyone (including Meikle himself) before 1967. Up until 2010, the cut-off date for records in The Flora of County Fermanagh that was published in late 2012, there were only eleven records of this hybrid in the Fermanagh Flora Database. These few records were thinly and widely scattered across nine tetrads in the VC, which suggested that we were not recognising and recording this hybrid, or else that it was not anything like as common in Fermanagh as appeared to be the case further east in Cos Down and Londonderry (H38 & H40). The few records in Fermanagh at the time of the Flora publication (Forbes & Northridge 2012), came from a surprisingly wide range of habitats where the parent species overlap, including wood margins, thickets and hedges on lakeshores, by rivers, streams, in quarries or on roadsides. This rather strongly suggested that the hybrid was more frequent than had so far been recorded in the VC and this has proven to be the case since the online BSBI Database (accessed February 2020) now lists a total of 41 records, although a few of them appear to be duplicates and others require further validation before they can be fully accepted.

Genetic introgression following frequent back-crossing may have established a continuous series of intermediates forms between the parent species, leading non-specialist Salix recorders, including ourselves, to widen in our minds the variation acceptable within these two species. Thus we may be 'shoe-horning' shrubs into one or other of the species, rather than recording them as putative hybrid forms.

Hybrid occurrence elsewhere in Britain and Ireland

Having acknowledged this quite definite possibility, the evidence provided by the New Atlas map of this hybrid suggested that Meikle (1984) might have overstated the likelihood of finding this taxon in Fermanagh. The recorded hectad distribution of S. × multinervis appears more scattered than that of either of its parent species and, while the New Atlas editors regard the map as 'incomplete', our slight Fermanagh record in 2012 did not appear very different from, nor totally inadequate in comparison with many other VCs in B & I. The considerable increase in Fermanagh records in subsequent years, plus an addition of earlier records by experienced recorders now recognised as belonging here, means Meikle has been proven correct in his prediction.

The experience of Scandinavian botanists is similar and relevant to the above position: Jonsell et al. (2000, p. 181) concluded that, "most specimens identified as this hybrid belong to one of the parents". On the other hand, Howitt & Howitt (1990) claim that in Nottinghamshire (VC 56) and in some other lowland areas of Britain, including East Anglia, S. aurita has, "hybridised itself out, or has been lost through drainage". It has to be said, however, that the New Atlas maps of S. aurita and of this hybrid indicate that even to begin with S. aurita was never very strongly present in the lowland areas of the Midlands and SE England (Preston et al. 2002).

The updated hectad map of B & I provided by Stace et al. (2015) confirms that S. × multinervis is more common and widespread throughout both islands than previously was thought. These authors consider it unlikely that hybridization directly causes any decrease in S. aurita, but rather that replacement of the latter is more probably due to decreasing fitness of the species to cope with the current rapidly changing environment (Stace et al. 2015).

A further examination of the records listed in the FNEI 3 indicated that only a very few recorders in the three Irish VCs covered by this Flora were able or willing to recognise this hybrid. For discovering this and other willow hybrids in NI, John Harron deserves particular mention (Hackney et al. 1992). The suspicion that this hybrid is being regularly overlooked or mistaken for its parents by many recorders in Ireland and only recognised by a few, is strongly reinforced by the fact that Daniel Kelly (1985) published records of S. × multinervis in six other Irish VCs apart from Fermanagh (ie in N Kerry (H2), Mid Cork (H4), N Tipperary (H10), SE Galway (H15), Offaly (H18) and Leitrim (H29)). The habitats he lists ranged from damp mixed woodland margins and hedgerows to the cut-away margin of a bog (Kelly 1985).

Additional evidence supporting Meikle's contention comes from Green (2008) who found this hybrid was the second most common willow after S. cinerea subsp. oleifolia in Co Waterford (H6). He found it occurred from sea level to high in the mountains, and only rarely appeared along with both parents. It is clear from this, and from the wide range of habitats in which S. × multinervis has been recorded, including along rides in conifer plantations, banks of rivers and streams, in disused quarries and railways and on rock faces in mountain coums (Green 2008), that R.D. Meikle, who verified some of the Irish vouchers, is absolutely correct in believing this hybrid to be of frequent occurrence in Ireland.

Threats

None.

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