Posted: 13/08/2014 at 09:51
As you suggest, I think the roots should be a help in trying to identify your plant and could indicate that it is in the same family as Clematis - i.e. ranunculaceae.
Clematis all have compound leaves, to my knowledge - but other members of ranunculaceae have simple leaves.
It's certainly worth growing it on and seeing how the plant develops as this will give more clues as to its id. Seedlings can have immature foliage.
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