202/365: Mystery Plant

Does anyone recognise this plant? From the shape of the skeleton leaf I posted here, Ladkyis thinks that it may be Japanese Knotwood.

 

When the shed was demolished, this pot was found squeezed behind it.  There are two plants in the pot, both of which have probably self seeded.  The other is easily recognised as a bramble but I don't know what this one is - even with watering it hasn't grown much!  If it is the dreaded Japanese Knotwood at least it is contained in a pot and it can be incinerated easily.