The altitude, distance to the source of infestation and land use systems in upstream areas best predict its establishment. We presumed that under the shadow of its Kinyarwanda name ‘u-mu-gey-o’, M. pigra was able to spread and become an invader before scientists could take notice of its true identity: an invasive [not environmentally harm-less] alien [not Rwandan-native] Mimosa [not Acacia, Ptelorobium, Caesalpinia nor Rosa] species.