True Tubers and Root Tubers

To put it simply, having a tuber root means that a plant grows a thickened area so it can store nutrition and water during the coming winter.  Once winter has passed, the tubers will use the storage units to reproduce themselves.

There are two types of tubers, stem tubers and root tubers.  Stem tubers are true tubers and generally grow their storage units from the sides of rhizomes or stolons.  Their cell structure is a stem.  Stem tubers are usually oblong or somewhat rounded with visible nodes.  They are often near the top of the soil.  Stem tubers that develop underground are often temporary, and then used to produce young plants.  Stem tubers that develop storage units above the ground will drop them to reproduce.  A couple examples of stem tubers are the tuberous begonia and cyclamen.

Root tubers, or tuberous roots, are secondary lateral roots.  They are quite similar to stem tubers with a few differences.  Their cell structure is of root.  Another difference is that the end that is attached to the parent has crown tissue where the foliage and stems grow.  The roots grow at the other end.  With true tubers or stem tubers the end that is attached to the parent is the opposite.  Root tubers live for two years, making them biennials.  It will live its first year as a tuber.  The following year the tubers will grow foliage and flowers.  After it is finished blooming, the mother plant will develop tubers as it dies in the fall.  Examples of tuberous roots are daylilies, sweet potatoes, and dahlias.  Root tubers can be dug up and divided as long as they have a crown.