Both Jane McGary and, in a private response to my Begonia boliviensis “Fireworks’ post of a few weeks ago, another list member, seem to be gently taking me to task for calling the underground parts of the Chilean Tropaeolum and Begonia corms instead of calling them tubers. I would argue that corm is a more inclusive and appropriate term. The etymology of the word corm (it’s derived from the Classical Greek word for tree trunk or stump) calls attention to the fact that the structure in question is a stem of some sort. And corms are the true perennial stems of the plants in question. In another recent post, Jim Shields mentioned pseudobulbs. This term in my experience is used exclusively for orchids, yet the structures in question seem to be corms. The structure from which Pleione grows is little different than the structure from which Colchicum grows. The way I think about it, the corm is the basic structure which these plants have in common: corms are the modular perennial stems of these plants. All true bulbs have at their core a corm (in the sense that the basal plate is the perennial stem of the plant, in effect a corm). Many corms seem to have evolved from ever shortening rhizomes, something easily seen in the Iridaceae. But I don’t think our concept of corm should be limited to what we see in the Iridaceae. That we have several terms for what seem to be essentially comparable structures is not surprising: the plants which have evolved with these structures are not necessarily closely related. Most of the geophytes we grow are monocots, but a few are dicots (Begonia, Cyclamen, Dahlia, Oxalis, Tropaeolum and many gesneriads are familiar non-monocot examples). These non-monocot plants have not shared a common ancestor with the monocot plants since the early Cretaceous (i.e. perhaps as much as 145 million years ago), and there is no reason to think that corms are inherited from a common ancestor - rather it makes sense to assume that they developed independently over and over in different groups, so we should not be too surprised that the morphology of corms varies. The next time you are about to call something a tuber, give some consideration to the fact that the structure in question might be the modular perennial stem of the plant in question, in other words a corm. Jim McKenney jimmckenney@jimmckenney.com Montgomery County, Maryland, USA, 39.03871º North, 77.09829º West, USDA zone 7 My Virtual Maryland Garden http://www.jimmckenney.com/ BLOG! http://mcwort.blogspot.com/ Webmaster Potomac Valley Chapter, NARGS Editor PVC Bulletin http://www.pvcnargs.org/ Webmaster Potomac Lily Society http://www.potomaclilysociety.org/