Ok, from what I've gathered, with the plants in cultivation, there is very very little difference, exept maybe in the fact that burkie seems to have yellower leaves. The plant I have looks the same as the burkie tony has pictured on his website, but even that burkie looks like one of the ventricosa he has pictured. They look almost the same. Between clones similar to those, I really dont think it justifies them being a different species. The only true genetic burkies may be the ones in the wild, pictured in that one article posted a while back. Perhaps what is in cultivation is a mixture of ventricosa and burkie, originating from hybrid plants in the wild perhaps. That may explain some of the variability in cultivated plants, but I really dont know. There should be a study of variability of both species in the wild.