A plant axis (PO:0025004) that is radially enlarged. [source: POC:curators]
Comment
Functions in storage of photosynthate metabolites. May develop from a branch (PO:0025073) or a root (PO:0009005). If you are annotating to tuber, you should pick the more specific child term: shoot axis tuber (PO:0004543) or tuberous root tuber (PO:0025476).