Tubers vs. Rhizomes: What’s the Difference?

Stem tubers, or true tubers, are bulbous modified stems that grow underground. The tuber grows underground to store nutrients for survival and reproduction through the winter for future growing seasons. Tubers growing underground are connected to the original stem by new stem-like off-shoots called stolons. Characteristics of a stem tuber include leafy plants, high starch content, and a tendency to grow near the soil’s surface. Common examples edible of tubers include potatoes, jicama, sunchokes, and yams.

Root tubers (like sweet potatoes or cassava) are often mistakenly classified within this category, but because they have swollen roots (rather than stems) they don’t fit the technical bill for what a true tuber is.

A rhizome is a type of plant stem that grows horizontally underground and sprouts new plants from nodes on its surface. The rhizome’s main purpose is to store carbohydrates and proteins so the rhizomatous plant can survive between growing seasons. Examples of rhizomatous plants include ginger, turmeric, asparagus, lily of the valley, and canna lily.

Tubers and rhizomes are both modified underground plant stems that serve as storage organs, but they function in two slightly different ways:

• Growth pattern: Tubers can grow in any direction, while rhizomes grow horizontally under the ground and sprout new growth along the underground stem as they grow.
• Reproduction: Both tubers and rhizomes can create new plants, but they do it in slightly different ways. Tubers have nodes (often called “eyes” on potato tubers) that appear anywhere on the flesh and sprout both new shoots and new roots, while rhizomes sprout roots along the bottom of the growth and stems along the top.

There are a number of underground crops that are mistakenly categorized as true stem tubers. Some of the plants mistakenly identified as tubers include:

• Root tubers: Root tubers are characterized by swollen roots which store their nutrients. Examples of edible root tubers include sweet potatoes/batatas and cassava/manioc (root tuber). Other plants growing from tuberous roots (that aren’t edible) include dahlias, daylilies, peonies, cyclamen, and tuberous begonias.
• Summer and spring bulbs: Bulbs have swollen underground stems similar to tubers, but their growth patterns are different. New bulbs grow from the base of the original bulb, while tubers develop buds on their surface, and new stems sprout from there. Examples of edible bulbs include onions, shallots, and garlic. Examples of inedible bulbs include daffodils, amaryllis, crocuses, tulips, cannas, gladiolus, and hyacinths.
• Corms: Corms have a swollen underground stem for nutrient storage, like stem tubers, but corms have a basal plate (the flat part of the plant where the root grows) while tubers don’t. Examples of corms include taro (also called cocoyams or malanga), caladium (elephant ears), and freesias.

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