INCOMPLETE SAMPLING. “If we, in principle, accept that interspecies lateral gene transfer (LGT) was involved in the assembly of such complex prokaryotic structures as the photosynthetic apparatus or type III secretion systems, we must also allow that the true histories of many nonmitochondrial eukaryotic cellular features are complex and reticulated, only appearing linear because of extinction and as yet poor sampling of available diversity.”
http://www.pnas.org/content/112/33/10278.full