International audienceRelations within the Iranian branch of Indo-European have traditionally been modelled by a tree that is essentially composed of binary splits into sub-and sub-subbranches. The present article will argue that this tree is rendered outdated by new data that have come to light from contemporary and ancient languages, and that it was methodologically problematic from the outset, both for reasons of the isoglosses on which it is based and for not taking into account distinctions such as shared innovations vs. shared archaisms and marked vs. unmarked language changes. Conversely, a set of non-trivial morphological innovations, particularly in the verbal system, shared by Bactrian, Parthian and some neighbouring languages app...