This appeared in a friend's garden last year but we've no idea what it is. Photo shows this year's growth, the cut stems are bamboo-like hollow. Flowers appear july/August very small, white inside and purple outside, in clusters that hang down like upside-down lupins 3 - 4 inches long. We've discounted Japanese knotwood because it lacks the purple flecks on the stems and the flowers are the wrong colour. Any ideas?