Ranunculus subgenus Batrachium
Once again I might just raise more questions than answers on this one but it’s an issue of accuracy of recording so I think worthwhile.
The River Aller is not a long river, four monads just about covers it and then it joins with the Horner stream just before Bossington and then short distance to sea. Ranunculus fluitans is on the Rare Plant Register as scarce in VC5 so an important plant. At the start of River Aller R. fluitans is recorded after that either R. penicillatus or R. penicillatus subsp. pseudofluitans is recorded and indeed in most cases both are recorded. Now this is a stream that in most of its length is just 2-3 metres wide, fairly fast flowing and instincts suggest only one Water Crowfoot is likely to be present (but not certain). Indeed in the top monad where R. fluitans is recorded the length of leaf is long , well in excess of adjacent node and coupled with few divisions of leaf it has not unsurprisingly been recorded as R. fluitans in past. By the end of that monad and indeed probably only 70m from the longer leaved R. fluitans there does appear at first glance a change of taxa which seems to continue for next three monads and as already said recorded variously as R. penicillatus and/or R. penicillatus subsp. pseudofluitans.
Ranunculus fluitans in River Aller.
Only one option, have a closer look and to cut a long story short I did not have the skills to make a determination that I was certain of. Richard Lansdown was very obliging and took a look at a good flowering sample; indeed a voucher from the patch where the longer leaved R. fluitans seemed to have a change of jizz to shorter leaf was sent to him
This is the summary of his email;
I have had a look at your plant. The leaf divisions would make it R. fluitans. This is an excerpt from a forthcoming key (not mine), I think that the caveat fits.
Large plants, robust, laminar leaves absent, capillary leaves exceedingly long, fleshy, subparallel, final segments less than 50, petals 6-12, receptacle glabrous……………………………………………………. R. fluitans Lam
Remark: Plants with 1 or 2 deviating characters should be identified as ‘R. cf. fluitans’. They indicate historical Introgression. Plants with more deviating characters are regarded as R. fluitans hybrids of which the second parent species is indeterminable.
I would say that yours has the receptacle which is not glabrous, I don’t think that the leaves are particularly long or very fleshy but they definitely have fewer than 50 ultimate segments. So yours could probably be called R. cf. fluitans or possibly a R. fluitans hybrid.
I think that this key has real honesty and suspect that it will make decision-making easier. However, most populations will not be named to a species, so many people will not be happy.
So, using Richards’s guidance I have looked at all the River Aller Water Crowfoot and it is looking like all the River Aller Ranunculus is in-fact R fluitans (or possibly a hybrid) despite some variation in leaf length. I did find Richard’s guidance on receptacle a useful feature.
Just one more photo.
Ranunculus fluitans receptacle.
A new key might well be worth the wait but equally I thought I would highlight some issues with this difficult taxon. Examination can be done in the field and the photo shows the sparsely hairy receptacle (with a few carpels removed) of fluitans. This is important character in Stace 4 key and the above sparsely hairy or indeed sometimes glabrous receptacle is one feature in separating fluitans from the densely hairy penicillatus, The online Plant Crib is best for guidance on rest of the main features for identification.