The small Guineo-Congolian tree Alchornea cordifolia (Euphorbiaceae) has been observed to dominate the undergrowth in an open type of southwest Ethiopian riverine forest not recorded before. The nearest previously known records of this species were at the South Sudan–Congo border and in Uganda and Kenya near Lake Victoria. The newly discovered range extension of A. cordifolia matches that recently discovered for Zanthoxylum gilletii De Wild. (Rutaceae), found as new to Ethiopia in 2006, and is found to be congruent with previous known disjunct distributions of Guineo-Congolian-Ethiopian species. A new account of the genus Alchornea in Ethiopia, including A. cordifolia, is provided in the format of the Flora of Ethiopia and Eritrea.