I've never actually seen one. It was the sepals that made me think of Dahlia then I searched the species knowing it wouldn't be a cultivar.
Chris, my response was perhaps a little unclear. It's not D. imperialis. But congrats on getting the genus.
Since interest in this one did not continue, it's time to give the answer. It's Dahlia tenuicaulis, which I think has been spread around to a limited extent. It's one of the tree dahlias but only gets about 3 m tall or a trifle more, not as tall as D. imperialis. Foliage is slightly different from other dahlias, with thin, broad leaflets of a somewhat purplish green shade, and the flowers are only about 3 in diameter and not at all conspicuous, but an interesting colour -- and have been appearing continuously now for almost 5 months, far longer than flowering of D. imperialis. Not a plant of much ornamental value, but if I ever find time to take up plant breeding, this is one I'd like to play around with. Here's the fully open flower
Its lovely would look great in my jungle. I have what I know as a tree dahlia growing in several parts. The flower seems to be a paler mauve and the things are very tall about 5 meters if the wisteria holds them up. I have also found that If I am not careful how I get rid of the cut down stems they just keep going hence a bit of a weed. Thanks for the information Liz
If you'd posted the second pic rather than the first, I might have got it ;-) . . . there was a pic of it in the RHS magazine 'The Garden' a while back which someone had taken on Nevada de Colima in Mexico. Might even have been the source of the seeds which you're growing now. But the half-open flower pic was different enough to put me off suggesting it.
