New clematis are introduced every year so a book is always going to be behind the times. There are hundreds of clematis now and new ones coming available.
Get to know this site instead - http://www.clematis.hull.ac.uk/ It is regularly updated and includes descriptions, sizes, pruning groups, breeders, parents, country of origin and so on and so forth.
Another good place to research is the websites of clematis nurseries such as
@Claire204 , it depends how deeply you want to delve into the world of Clematis. I have a small paper back book called Clematis The Royal Horticultural Society by Charles Cheshire. It doesn't list every single clematis, but has colourful pictures of a wide variety of clematis, descriptions, times to prune, training, cuttings, raising them from seed, positioning and which type of shrubs and trees they can grow up/over etc. etc. I bought my book for £4.99 5 or 6 years ago, and it is often available on Amazon.
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Get to know this site instead - http://www.clematis.hull.ac.uk/ It is regularly updated and includes descriptions, sizes, pruning groups, breeders, parents, country of origin and so on and so forth.
Another good place to research is the websites of clematis nurseries such as
https://www.hawthornes-nursery.co.uk/
https://www.clematis-nursery.co.uk/
https://www.taylorsclematis.co.uk/?gclid=EAIaIQobChMIyvPhhLzr4gIVS0HTCh35pw_kEAAYASAAEgJb0PD_BwE
https://www.thorncroftclematis.co.uk/clematis.html
There are more so you can google and find the one closest to you if you prefer to see before you buy.
😊