I'd like to comment on the vigour, size and beauty of the lowii hybrids. I find that despite lowii's slow growth and smaller size, its hybrids are beautiful, being often larger than either parent, and sometimes faster growing than either one, which amazes me because a slow species like lowii... well you wouldn't expect it to give hybrid vigour. It's quite amazing.
Hybrid vigour is not just taking into account the types of genes from both parents, but the total interaction between the genes from both parents. That's what makes it very intriguing and a bit complex to understand.