Wikipedia
"Cap-o'-Rushes" is an English fairy tale published by Joseph Jacobs in English Fairy Tales.
Jacobs gives his source as "Contributed by Mrs. Walter-Thomas to "Suffolk Notes and Queries" of the Ipswich Journal, published by Mr. Lang in Longman's Magazine, vol. xiii., also in Folk-Lore September, 1890". In the latter journal, Andrew Lang notes the folktale was "discovered" in the Suffolk notes by Edward Clodd.
Marian Roalfe Cox, in her pioneering study of Cinderella, identified as one of the basic types, the King Lear decision, contrasting with Cinderella itself and Catskin.
It is Aarne-Thompson type 510B, unnatural love. Others of this type include Little Cat Skin, Donkeyskin, Catskin, Allerleirauh, The King who Wished to Marry His Daughter, The She-Bear, Mossycoat, Tattercoats, The Princess That Wore A Rabbit-Skin Dress, and The Bear.
It was the first story read on the BBC series Jackanory.