I'm fairly confident that Araucaria will not have got it wrong, but Antonia Fraser in "The Kings and Queens of England" gives Richard II as the last Plantangenet monarch, and treats the Houses of Lancaster and York as new dynasties, presumably as Henry IV was not a descendant of Richard II (though he was the son of John of Gaunt, Richard's uncle). What is the current opinion on this - were the Wars of the Roses fought between rival Plantagenet families?