IMPACT OF OUTGROUP INCLUSION ON ESTIMATES BY PARSIMONY OF UNDIRECTED BRANCHING OF INGROUP PHYLOGENETIC LINES

Some of the effects of including outgroup taxa on the branching patter n of the ingroup taxa are revealed by an artificial example, and illus trated with a more complex natural example involving the grass genus K engyilia. To reduce the total number of changes required by a branchin g pattern, parsimony may prefer to reduce the number of changes on tem porally long phyletic lines to more distant outgroups while increasing changes on temporally short phyletic lines within the ingroup. This m ay have the effect of bringing the ancestors that define monophyletic groups within the ingroup down to the phyletic line to the outgroup, w hich converts them to paraphyletic groups. Thus the inclusion of outgr oup taxa during parsimony may alter the branching pattern of the ingro up to destroy distinct monophyletic groups and instead create nested s eries of monophyletic groups, reminiscent of the chaining properties o f some phenetic methods. If similarities between ingroup and outgroup are true homoplasies, then removal of these homoplasies will produce e rror. However, parsimony estimates of ingroup may produce bogus monoph yletic groups because no account has been made of the ingroup's most r ecent common ancestor.