Cultivars (contraction of cultural varieties) can be divided into two main groups:
Mutations or sports
Occur when a species or a cultivar develops an aberrant form: e.g. a blue plant with a yellow margin that grows a sport that's yellow with a blue margin.
Hybrids or crosses
This is a cross between two species, between a species and a cultivar or between two cultivars.
Which cultivars can you find here ?
Because of the enormous amount of cultivars that exist, I can't treat them all. If you're looking for the largest collection of pictures, The Hosta Library is the place to look, if you're looking for descriptions and other data, consult Hostamania by Hugo Philips.
So, what do you find here. Under "Hosta Mill Cultivars", in time you'll find detailed information on all plants growing in The Hosta Mill. Because of my personal preference for uniformly colored plants, most of them will be in that category.
Furthermore you'll find a round up of cultivars originating in Holland or Belgium. In time, I'll try to add as many interviews with the breeders.