hmm, interesting one this. I'm still doing research, but I haven't found it yet which doesn't bode well for a positive SU attribution. Tho, if any one can trace it, it'd be Marcus of course!
I have a couple, and bought my first some years ago. I',m pretty sure I have a jardiniere form somewhere as well, which would be consistent with many Sklo Union factories (vases and jardinieres as part of the range) - but doesn't mean it certainly is. Even then only certain designs were produced in both forms. Of course, thank to Marcus, we also now know that the birdbath base doesn't guarantee that it is by a Sklo Union factory. A sensible thing to do would be to compare colours to known SU designs, but I'd need to go and get and then unpack my collection - always a delightful treat, but alas I have no time right now. Does anyone else have a large collection and time?!
Personally it is one of my favourite Central European pressed glass designs, regardless of what it actually is, along with the dark green Jan Sylvester Drost design on Marcus' site. 'T would have been nice if the Drost had been SU, but once you get over it and look at the vase... :-)