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Reading the "official"book of Basque flowers edition 1999, both are very similar, and there is no mention about the length of hairs. Of course R. bulbous would show a bulb, but as I don't have a picture of it, the only difference I can see from drawings are the length of division in leaves. Apparently the bulbous has a slightly more deep division than sardous... so according to the picture I took, you may well be right
... and see if that's any help. (There are several varieties of Ranunculus bulbosus in Spain.)
In Britain Ranunculus sardous is the "hairy buttercup", so I expect it to be more prominently hairy than the other species, but the photographs I looked at online looked pretty similar to Ranunculus bulbosus.
Ranunculus bulbosus is a grassland plant (in my experience a plant of short grassland), whilst, in Britain at least, Ranunculus sardous is an arable weed, so your habitat is a point in favour of the former.
Congratulation "lavateraguy" ! I went back t othe flower and it has a bulb... no doubt anymore
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