The game is explained by the examples below,
starting with the simple,

Betula 'Clarke' and Scilla 'Black'
Bletilla 'The Hun' and Sorbus 'The Greek'.

To the more interesting varieties of,

Cytisus 'Kane'

and the pride of the collection, that vindictive little crab,

Malus 'Aforethought'

Hosta 'La Vista' [With thanks to Walter Gilmour]
Aloe 'Sailor'
Canna 'Shove yer Granny aff a Bus'
Phlox 'of Sheep' [This is an actual cultivar of Phlox drummondii ]
Sorbus insignis 'And in 'elf'

If you have any good ones, please email them to me.

Gold stars will be awarded!