Just as daisies and dandelions can all appear the same when you start taking an interest so buttercups can seem a challenge too. As always, with a bit of care they are actually not that difficult, you just have to look beyond the flower.
With the lesser spearwort (Ranunculus flammula) the clue is in the name 'spearwort'. The yellow five-petalled flower is much like most buttercups but look at the leaves and they are pretty unique in the buttercup family; they are pointed or spear-shaped. The lesser spearwort can be quite a variable flower and it has taken me by surprise on a couple of occasions but the spear-shaped leaves are always the key. There are two other features that help confirm the species. Firstly, the stems are usually reddish in colour. This is not the only species of buttercup with red stems but there are not that many. The other feature is that lesser spearwort always grows in wet places. Again, not the only buttercup that occurs in such places but there are only a few.
You can buy spearwort for your garden pond but I am not sure it is a good idea. It certainly has attractive, but plain, flower from May right through until September but it spreads by rhizomes and can quickly take over a small pond. I speak from experience.Lesser Spearwort: point well made