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Having found the remains of Dwarf Willow (Least/ Snowbed Willow) (Salix herbacea) in Lateglacial and early Holocene sediment cores during my M.Sc. dissertation laboratory work (more on this in later posts), I was keen to see it growing in the Lake District, where it is not infrequent (Halliday, 1997) before it dropped its leaves for winter. I've seen this diminutive 'tree' numerous times, both in the Lake District and up in Scotland, but staring down a microscope at its remains for hours on ends gives a certain new level of appreciation for the species. On a walk up Helvellyn from Stanah, Dwarf Willow is present for the majority of the high exposed ridge from Raise to Lower Man. I found the taxa in two distinct areas- the first of these is as a prostrate carpet on exposed plateaux areas surrounded by other high altitude taxa such as Alpine Lady's-mantle (Alchemilla alpina) and the second was within bedrock crevices. For me, the best and largest specimens can be found on the bedrock exposure south-east of the Raise summit (NY 34248 17405).
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| Showing the diminutive size of Dwarf Willow. |
One of the most interesting aspects of the visit to see the Dwarf Willow was the presence of foliar diseases and galls- it would be interesting to know if these associated fungi and galls were represented in the Lateglacial sedimentary record, as while I did not find any afflicted remains, it is surely likely that they would have been present.
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| Foliar diseases and galls on Dwarf Willow (Salix herbacea) from Raise summit (12-09-21). |
The most prominent of these are galls- large, elliptic galls that protrude from the leaf, red/green in colour with a smooth and shiny surface, are quite prominent. These galls are formed by two species of Sawfly (Euura herbaceae/ E. aquilonis) which are indistinguishable based upon the gall, with identification only possible through extraction of the larva.
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| Sawfly gall (Euura herbaceae/E. aquilonis) on Dwarf Willow (Salix herbacea). |
I took some fallen leaf samples of Dwarf Willow for my plant macrofossil reference collection, and when I looked through these samples I found an unusual leaf that displayed a series of black shiny legions. I have identified these black spots as Willow Tarspot Fungus (Rhytisma salicinum) which is a species of fungus, within the same genus as the ubiquitous Sycamore Tarspot, that afflicts numerous species of willow. Interestingly, the Willow Tarspot Fungus, according to NBN Atlas, has only recorded twice within Cumbria, with the only confirmed record from Sandscale Haws (31-08-1999), where Dwarf Willow is not recorded suggesting it was present on another Salix species. This is almost certainly due to under-recording than true absence. However, while I have also checked the CATE 2 database it may be that I cannot access all records of this species, hence I plan to check that it hasn't been recorded with my local records centre.
One associated affliction that I did not look for was Melampsora arctica - a rust fungus that I will surely keep an eye out for in the future.
Halliday G. 1997. A Flora of Cumbria. Centre for the North-West Regional Studies. University of Lancaster.
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