  The Yule model and the coalescent model are two neutral stochastic models for
generating trees in phylogenetics and population genetics, respectively.
Although these models are quite different, they lead to identical distributions
concerning the probability that pre-specified groups of taxa form monophyletic
groups (clades) in the tree. We extend earlier work to derive exact formulae
for the probability of finding one or more groups of taxa as clades in a rooted
tree, or as `clans' in an unrooted tree. Our findings are relevant for
calculating the statistical significance of observed monophyly and reciprocal
monophyly in phylogenetics.
