This came out of a packet of seeds of mixed perennials - or it might be from a seed in my worm compost. It was planted last year and was small over the winter (~ 2"). Then it started to grow in late spring - tall enough to be transplanted into the garden - next to a Rudbeckia. By then it had doubled to 4". Slow growth until about four weeks ago when it became a monster - about a metre + tall.
Originally with the colour and sheen of the leaves, I thought maybe Dahlia, but now I haven't a clue.
Can you help?
Yes, it seems to be Nicandra physalodes - it has started to develop those very distinctive 'ridged' flower buds.
Thank you fixpix. I'm not sure I would call the stems black, though.
Also, now I think of it, I swapped some seed and got a small pack of Nicandra physalodes - I must have mis-labelled them.