It doesn't look like ground elder to me.
http://sos-gardening.com/images/ground_elder.jpg
More like a relative of shepherd's purse (but not that, as the see dpods are different)
In addition ground elder (Agopodium podograria) is not the same as the elder tree (Sambucus) - they're not even in the same family (unless they've been reclassified since the publication of the reference book I use)
Duuno what it is, except it's a weed of some sort and Louie doesn't like it
Cow parsley with not many leaves?