Figure 3
From: A scalable method for identifying frequent subtrees in sets of large phylogenetic trees
T 1 is an input tree built on four taxa a 1 , a 2 , a 3 and a 4 . The internal nodes of T1 are labeled as x0, x1 and x2. S1 is the only seed obtained from T1 when k = 2 and c = 0. That is S1 is identical to the clade rooted at x2. S1, S2 and S3 are the seeds extracted from T1 when k = 2 and c = 1. They are all extracted from the clade rooted at x1 by contracting a3, a2 and a1 respectively.