This is a Dog Violet (Viola conspersa) and one of those finds that you nearly miss altogether. Actually i nearly stepped on it. I found it among a patch of Ash regeneration and it was in a solitary clump..JPG)
Dog violet are a type of plant which fertilizes it self which can explain why i found this one on its own. Also Violet species are a good source of early nectar of butterflies and a host for their larve. For more information about this plant or any other woodland plant here is a good site to look at.
