Hybrids are usually designated with an 'x' to clarify it's a hybrid, rather than a distinct species.
I've heard that this rule is waived in the case of naturally occurring, fertile, stable hybrids.
Is this correct?
Thus, D. spatulata x D. rotundifolia = D. tokaiensis, rather than D. x tokaiensis, because it is natural, fertile, and stable.
What about S. x wrigleyana? I know it's naturally occurring... is it fertile and stable? Can it be written as S. wrigleyana?