On Tormental Potentilla erecta
No identification made yet.
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This looks similar to herbicide damage that occured in my garden - it seemed to particularly affect leaves that are dissected or serrated.
A couple of years ago there were problems with aminopyralid herbicides that persisted in manure
See where your coming from, but... highly unlikely. The plant/s* infected only have isolated leaves that have succumbed. More importantly the habitat is the stretch of land, some 8+ M's wide, and runs for many kilometers between the water margins and flood control banks of the River Witham, (Upper**). The plant is common to both sides of the river, as to whether I have the correct ID for it, well that's another question.
Back to the cause you suggested, and why I think it could be a doubtful one. Two good reason that lead me to thinking herbicide is not the cause. The first one being the flooding of the habitat, once a year guaranteed. The second, the actual stretch, it falls between Russel Street bridge, and what is known as laundry bridge, (Altrim Terrace), well with in the boundary of Lincoln City its self.
Now bearing in mind that what I write are only transcriptions of my thoughts, of the time, and those induced by good folk such as your self. So on rereading, and noting the mention of manure and remembering from whence it comes, has me now thinking that you could be on to something. Swans, (Mute), geese, (Canadian, Graylag), all seen on a daily bases, and all grass grazers. All of which are often recorded, (in huge numbers), out in rural areas grazing farmland pastures. All end up back on the waters, (and banks of), to roost, and do what all animals do, defecate. Beggars the question, are farmers using herbicides to eliminate broad leaved weeds in what are potential hay pastures..? All could account for the isolated cases of what could be, as you suggested, herbicide damage.
Just airing my thoughts...
* Possibly more than one plant affected.
** The Upper River Witham, the stretch from its source,(South Witham), to the Brayford Pool Lincoln City.
An iSpot Project- HELP WITH IDS - UK & Ireland Community - PLANTS
There are no galls that look like this caused by mites, insects or fungi in Redfern & Shirley's British Plant Galls (2002 edition).
It does look like a gall at first glance, but perhaps it is not, as Mark says.
University of Edinburgh and Biodiversity Observatory (OU)
Lat/Lng: 53.1914, -0.5646
OS grid ref: SK960669