While bulbs are used interchangeably with corms, tubers and rhizomes, each are botanically different. Here is an illustrated guide on what the differences are between each of these terms.
Bulbs are a collection of underground leaves. The contain food for the plant, which grows out from the center of the bulb. All bulbs are monocotyledons (monocots) which have only one embryonic leaf. All monocot flowers have flower parts in groups of three (such as 3, 6, or 9 petals). When a true bulb is halved, visible layers (the actual underground leaves) are present, unlike tubers, corms, and rhizomes. An example of a true bulb is the shallot.
Corms are underground stems used for food storage. Corms are not ‘true’ bulbs (when halved, no layers are present). Cormels are smaller corms growing from the base of the main one, which produces a new plant. An example of corms are water chestnuts.
There are two types of tubers – stem tubers and root tubers.
Stem tubers are underground stems. They have the same parts a normal stem has. Stem tubers are grown to be perennial where the plant grows new every year. They are perennating organs, which protect themselves to survive and germinate another season. An example of a stem tuber is a potato.
Root tubers are underground roots with a piece of the stem attached. They are biennial in nature. The plant shoot dies one year leaving the new root tuber where the next plant grows, storing nutrients in the roots for the next year’s tubers. An example of root tubers are beets.
Rhizomes are thick, short stems found underground, sending both roots and plant shoots from the nodes. Examples of vegetable rhizomes that are grown for their above ground stems are asparagus and bamboo. Examples of rhizomes that are grown for their underground stems are ginger and turmeric.