Botany within your reach. 3. Potato tubers are stems.

It's always nice when other people help the cause.  So here's a link to a nice discussion about potato tubers. When things grow underground there arises considerable confusion about whether they are roots or stems. There are three kinds of subterranean storage stems: horizontal ones often near the surface are called rhizomes (ginger)(labeled "ginger root" but it's a rhizome), short erect ones called corms (taro), and elongate to globular ones are called tubers. Tubers can also grow aerially.  So like all good stems potatoes have leaves, highly modified, and buds ("eyes")that give rise to branches. This is well illustrated at the link above.  And then these branches can give rise to roots, and ultimately to new plants. This was an idea TPP was going to do for his BWYR series, but this blog was just too good to pass up.  HT and many thanks to the Botanist in the kitchen blog. TPP provides a regular feed so you can just look for them in the blog roll side column.
For the record sweet potatoes are roots but have a stemish quality at their proximal end. True yams are tubers, but in North America, yams are a variety of sweet potato.