Storage Organ - Underground Storage Organ

Underground Storage Organ

In common parlance, underground storage organs may be generically called roots, tubers, or bulbs, but to the botanist there is more specific technical nomenclature:

• True roots:
  • Tuberous root or root tuber — e.g. Dahlia
  • Storage taproot — e.g. carrot
• Modified stems:
  • Corm — e.g. Crocus
  • Stem tuber — e.g. Zantedeschia (arum lily), potato
  • Rhizome — e.g. Iris pseudacorus (yellow flag iris)
  • Pseudobulb — e.g. Pleione (windowsill orchid)
  • Caudex — e.g. Adenium (desert-rose)
• Others:
  • Storage hypocotyl (the stem of a seedling) — sometimes called a tuber, as in Cyclamen
  • Bulb (modified leaf bases) — e.g. Lilium, Narcissus, onion

Some of the above, particularly pseudobulbs and caudices, may occur wholly or partially above ground. Intermediates and combinations of the above are also found, making classification difficult. As an example of an intermediate, the tuber of Cyclamen arises from the stem of the seedling, which forms the junction of the roots and stem of the mature plant. In some species (e.g. Cyclamen coum) roots come from the bottom of the tuber, suggesting that it is a stem tuber; in others (e.g. Cyclamen hederifolium) roots come largely from the top of the tuber, suggesting that it is a root tuber. As an example of a combination, juno irises have both bulbs and storage roots.

Underground storage organs used for food may be generically called root vegetables, although this phrase should not be taken to imply that the class only includes true roots.