Her roses remain the most popular subject, but two other items are particularly notable. First, the book of detachable postcards published by Tuck and sold to watercolour artists. Each page had a full colour chromo-litho Klein postcard together with a monochrome outline postcard for the owner of the book to paint. Once complete both the Klein and the amateur artist postcard could be detached and sent. Second and best of all was her 'alphabet' series, 26 postcards each featuring a letter of the alphabet entwined with flowers. The alphabet cards were often sent as a love token to those whose names began with the letter and consequently assembling all 26 today can be a challenge.
Catharina Klein painted more than 2,000 different still life images which exist now only on postcards, calendars, and advertisments.