Tim, I know Musa is diverse and don't doubt that that diversity extends to rootstocks. Perhaps it is a case similar to Amorphophallus, but reversed: almost all amorphos grow from a more or less globular or discoid structure that is typically used up completely each season and is "replaced" by a new corm formed at (and by) the base of the current season's leaf and cataphylls. However, there is at least one species, A. coaetaneus, that could be described as forming a "chain of corms". Instead of being used up entirely in a season, the corms persist in rhizomatous fashion for several years. Thus, we may consider cormous plants-- certain irids, aroids and others-- to be derived from likely rhizomatous ancestors. It sounds as though this might be the case in Musa, too. I'm not aware of any proper Musa species that do not offset, but there are numerous amorphos that can and do make offsets-- together the mother and daughter corms could be thought of as an extremely abbreviated rhizomatous system (of corms). Dylan