The Phytomonas genus was created arbitrarily to designate plant trypanosomes. A serological study with polyclonal and monoclonal antibodies was carried out to situate these trypanosomatids with respect to other trypanosomatids - Herpeiomonas, Critbidia, Trypanosoma - and to compare different plant trypanosome strains with each other. The use of monoclonal antibodies directed against two different isolates makes it possible to distinguish plant trypanosomatids according to their geographical origin and to separate clearly the plant trypanosomatids from the South of France from other lower trypanosomatids, which seems to justify creating the Phytomonas genus.