Early branching eukaryotes?

Recent phylogenetic analyses suggest that Giardia, Trichomonas and Microsporidia contain genes of mitochondrial origin and are thus unlikely to be primitively amitochondriate as previously thought. Furthermore, phylogenetic analyses of multiple data sets suggest that Microsporidia are related to Fungi rather than being deep branching as depicted in trees based upon SSUrRNA analyses. There is also room for doubt, on the basis of a lack of consistent support from analyses of other genes, whether Giardia or Trichomonas branch before other eukaryotes. So, at present, we cannot be sure which eukaryotes are descendants of the earliest-branching organisms in the eukaryote tree. Future resolution of the order of emergence of eukaryotes will depend upon a more critical phylogenetic analysis of new and existing data than hitherto. Hypotheses of branching order should preferably be based upon congruence between independent data sets, rather than on single gene trees.