What is this sprouting tuber?

sort of looks Potato like, but I haven't introduced any potato or vegetable bulbs/tubers into this area?

 

Could be japanese anenome? Leaves are too young for me to tell.

 

The leaves look right for one of the tuberous Salvias. Maybe S.patens or one of the S.guaranitica cultivars such as "Black and Blue".

 

I haven't pruchased any Salvia bulbs either.. bit of a strange one really.. I certainly didn't, to my knowledge, plant anything there, but it is emerging from a tuberous structure as you can see.

 

Certainly looks like one to me though - I have a few coming back to life here. However, the tubers of those Salvia that grow them are usually vertical and in clusters like Dahlia tubers.