"Duncan" schreef
For no other reason than it interests me I'm trying to get my head
around the way plants are named.

Your example of Ajuga reptans 'Burgundy Glow' is an example of a
cultivar. As to the origin of the cultivar--natural, bred up, or purely
illusory and for profit, one can't know without some research...

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Note that it is no longer allowed to use "cv."
so it is Ajuga reptans 'Burgundy Glow'
(never Ajuga reptans cv. Burgundy Glow)
* * *

Ah, yes, clear as a clear thing, but still an excellent answer, thanks

I also have a Caryopteris clandonensis 'Heavenly Blue' in my garden I
really like it. More than Caryopteris clandonensis 'Worcester Gold'
anyway (horrid smelly spindly thing) .

One more question if you have time

Why do some people write Caryopteris x clandonensis ?

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A multiplication sign before an epithet indicates a hybridname. If a
multiplication sign is not available (for example in e-mail) a small letter
"x" is used. People may vary in their opinion if something is a hybrid, and
not all hybrids necessarily get a hybrid name.

PvR