In a message dated 6/20/2004 2:38:57 PM Central Daylight Time, pbs-request@lists.ibiblio.org writes: > The preliminary data that we have based on ITS sequences show two > migrations > out of Mexico... Interestingly, H. glauca (one of my > favorite Mexican species) is sister to the other two Mexican clades. > Hi, Nice work I'm sure, I've read some of your manuscripts and they are well done, and -well-thought-out. I've got to ask how you know that only tree branching occurred (clades), rather than reticulate branching (fusions) as well. The clades-only approach is inconsistent with the evolution of some plant species and I've been trying to understand how this issue is finessed or directly addressed, as opposed to sidestepped. So far I think I've mostly confused myself. When I've looked at single genes, it is easy enough to see proper clades. Recombination doesn't clutter the picture too much within a cistron. But whole genomes present another picture altogether. Hybridization events have produced some genomes that are fusions of clades and not bifurcations. Perhaps reticulation (where it occurs) only limits precision, while still allowing easy identification of major migrations? Conroe Joe LINKS: Reconstructing Reticulate Evolution in Species http://cs.utexas.edu/users/nakhleh/… Journey Into the World of Cladistics (if you dare) http://www.ucmp.berkeley.edu/clad/clad1.html