Oxford, Jesus College 20 contains the largest genealogical collection surviving in any medieval manuscript written in Wales prior to the second half of the fifteenth century. The collection has been fully edited three times: once by Egerton Phillimore, with corrections by J. Gwenogvryn Evans; a second time by Peter Bartrum; and a third time in Appendix B.2 below. The section on the children of Brychan Brycheiniog has also been printed twice by A. W. Wade-Evans, and a full transcript of the manuscript, including its genealogies, has appeared on the website of the Rhyddiaith Gymraeg 1300–1425 project. Aside from occasional discussion of individual pedigrees, the collection as a whole has never previously been investigated. A few useful comments have been offered by Alfred Anscombe and Peter Bartrum on particular aspects of the text, and Thomas Charles-Edwards has made some perceptive observations on the section dealing with the ancestry of Rhodri Mawr. This chapter offers the first full analysis of the text.

The purpose of the present chapter is to analyse the structure of the text as it is extant in the manuscript, with a view to disentangling the stages in which the various components of the collection were composed and assembled. By necessity, such an approach must work backwards, from the knowable facts about the surviving manuscript to the more speculative reconstruction of the textual history of the collection. The discussion begins with an account of the history of the manuscript, followed by an examination of its contents. The textual affinities of the contents argue strongly that the manuscript's scribes worked in or around Glamorgan or Gower, in the same milieu that witnessed the writing of the Red Book of Hergest, around the end of the fourteenth century. Attention then turns to the genealogical collection itself, and it is suggested that the present arrangement of the text is the product of a deliberate act of redaction, formally dateable to the period 1216 × c. 1400, but probably belonging to the thirteenth century.