Lonely Pair
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LONELY PAIR. Platycladus orientalis, Oriental arborvitae.
North side of Jordan Hall.
A lonely pair of trees is a (gene tree, species tree) pair that has only one coalescent history, or mapping of the internal nodes of the gene tree to edges of the species tree that represent possible locations for the gene lineage coalescences to take place (Rosenberg 2019). Most (gene tree, species tree) pairs, like most tree pairs on the campus, are not lonely.
Photo: Noah Rosenberg, September 15, 2018