This is a page from the Graziano Haggadah, a 13th century haggadah on loan to the Met from JTS (see here). While wandering through the museum today the page caught my wife Ariella's eye because of the picture used for maror. Unless she and I are very much mistaken, that is a radish -- not a horseradish, just a plain old radish. I've never heard of anyone using a regular radish for maror. Granted that just because this haggadah was printed in the 13th century doesn't make it a rishon, but it is interesting if using radish was in fact the minhag of Catalonian Jewry.