  The perfect phylogeny problem is a classic problem in computational biology,
where we seek an unrooted phylogeny that is compatible with a set of
qualitative characters. Such a tree exists precisely when an intersection graph
associated with the character set, called the partition intersection graph, can
be triangulated using a restricted set of fill edges. Semple and Steel used the
partition intersection graph to characterize when a character set has a unique
perfect phylogeny. Bordewich, Huber, and Semple showed how to use the partition
intersection graph to find a maximum compatible set of characters. In this
paper, we build on these results, characterizing when a unique perfect
phylogeny exists for a subset of partial characters. Our characterization is
stated in terms of minimal triangulations of the partition intersection graph
that are uniquely representable, also known as ur-chordal graphs. Our
characterization is motivated by the structure of ur-chordal graphs, and the
fact that the block structure of minimal triangulations is mirrored in the
graph that has been triangulated.
