Early branching eukaryotes?

Recent phylogenetic analyses suggest that Giardia, Trichomonas and Microspo ridia contain genes of mitochondrial origin and are thus unlikely to be pri mitively amitochondriate as previously thought. Furthermore, phylogenetic a nalyses of multiple data sets suggest that Microsporidia are related to Fun gi 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 oi consiste nt support from analyses of other genes, whether Giardia or Trichomonas bra nch before other eukaryotes. So, at present, we cannot be sure which eukary otes are descendants of the earliest-branching organisms in the eukaryote t ree. Future resolution of the order of emergence of eukaryotes will depend upon a more critical phylogenetic analysis of new and existing data than hi therto. Hypotheses of branching order should preferably be based upon congr uence between independent data sets, rather than on single gene trees.