Hi Richard,

The issue of sample size in phylogenetic analysis is not well resolved, and it will generally depend on which quantity you want to estimate (e.g. branch length versus global substitution rate), see Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login for some discussion.

The standard approach here is to decide what you want to estimate and perform power simulations while varying various parameters that influence said power: rates, branch lengths, number of sequences, number of sites, etc.

HTH,
Sergei