We examined multiple plastid genes from a diversity of gymnosperm lineages to explore the consistency of signal among different
outgroups for rooting fl owering plant phylogeny. For maximum parsimony (MP), most outgroups attach on a branch of the
underlying ingroup tree that leads to Amborella . Maximum likelihood (ML) analyses either root angiosperms on a nearby branch
or fi nd split support for these neighboring root placements, depending on the outgroup. The inclusion of two species of Hydatellaceae,
recently recognized as an ancient line of angiosperms, does not aid in inference of the root. Cost profi les for placing the
root in suboptimal locations are highly correlated across most outgroup comparisons, even comparing MP and ML profi les. Those
for Gnetales are the most deviant of all those considered. This divergent outgroup either attaches on a long eudicot branch with
moderate bootstrap support in MP analyses or supports no particular root location in ML analysis. Removing the most rapidly
evolving sites in rate classifi cations based on two divergent angiosperm root placements with Gnetales yields strongly confl icting
root placements in MP analysis, despite substantial overlap in the estimated sets of conservative sites. However, the generally high
consistency in rooting signal among distantly related gymnosperm clades suggests that the long branch connecting angiosperms
to their extant relatives may not interfere substantially with inference of the angiosperm root.