Wooooah, wait a minute there Spec.....I *did* flower U. tricolor back in 1976: 6 scapes worth by golly, and I am still bragging about it, hee hee!!! I used the Copper method, pure dumb luck as it was the first time I had grown it, go figure. Back then I didn't realize how difficult it was to flower this species, so that must be the key.
Another species that I can't seem to get to flower is U. pubescens, although many claim it is not difficult. I think the plant senses my fear.