The Houses of York and Lancaster include all the claimants to the throne during the Wars of the Roses and were descendants of Edward III. The simplified family tree below shows how they were related to one another and to Edward III.
Richard II was deposed in 1399 by his cousin, Henry IV (Lancaster line – in red). At this time, Lionel Duke of Clarence’s heir, Edmund Earl of March, (Mortimer line – in blue) was only a child. (The Mortimer character in Shakespeare’s play, Henry IV Pt I, is a conflation of this child with his uncle, Roger’s younger brother, Sir Edmund Mortimer).
When Richard Earl of Cambridge (York line – purple) married into the Mortimer family (blue) he combined two potential claims to the throne. When Cambridge’s son, Richard Duke of York, eventually claimed the throne he did so through his Mortimer family line.
The Dukes of Buckingham (Stafford line – brown) were not senior enough to be considered as potential claimants, at least until 1483.