This over 1m tall, rigid upright plant is growing in a patch of bare earth in my Cornish garden. No sign of flower buds yet. It has elongated, fine toothed, unstalked hairless leaves in opposite pairs growing up the slightly furry unridged stem, about 3 or 4cm apart. Pairs of branches grow out at on opposite sides at the position of the stem leaves, symmetrically, all the way up to the top. Looks a bit like Great Willowherb, but isn't. Have also ruled out Caper Spurge. The plant has put out a stolon and a new plant is now growing from it. Can anyone identify it please?