Fig. 1.

Gene trees evolving on five-taxon and six-taxon species trees. (A) Five taxa. (B–D) Six taxa. The gene trees in (B)–(D) have the same unranked topology ((A,(B,(C, D))),(E, F)). Only the ranked gene tree topology in (D) does not match the ranked species tree topology. For each $i=1,2,\dots ,n-1,\hspace{0.17em}{s}_i\ge 0$ denotes the time of the ith speciation, τ_i represents the interval between the $(i-1)$th and ith speciation events, and u_i represents the ith coalescence (node with rank i) in the gene tree. Interval τ₁ has infinite length.