"Duncan" schreef in
OK ... I think ... so If a plant is named Caryopteris x clandonensis
'Heavenly Blue' I guess it means that someone thinks that 'Heavenly
Blue' is a hybrid between two plants of the species clandonensis.
Whereas if it was Caryopteris 'Heavenly Blue' then someone thinks that
it is a hybrid of several species of Caryopteris ...

***
Oh no. The cultivar epithet is entirely separate from the botanical bit, and
the "x" belongs tot the botanical bit, so:
* there are people who think
Caryopteris x clandonensis is a hybrid (hence the x)

* others think
Caryopteris clandonensis is a real species (no x)

PvR