Modified stems are plant stems that carry out special functions needed for plant survival in certain environments. These stems may have abnormal shapes and grow above or below ground.
Some modified stems grow above ground. Stolons run above ground or just beneath the surface horizontally. They are important for vegetative production. Stolons form nodes as they grow, which produce new plants. People commonly refer to stolons that grow above ground as runners.
Tendrils are slender stems that grow and twine around objects to provide support to the plant. Thorns are modified branches that protect the plant. Axillary bulb-shaped buds, or bulbils, store food and eventually fall off of the plant and produce new plants. Photosynthesis relies on cladodes, or green branches, that do not grow very long.
Modified stems that grow beneath the soil include tubers, bulbs, rhizomes and corms. Tubers, found on potatoes, may store starch. Appearing on the end of stolons, tubers are commonly referred to as eyes on potatoes.
Plants use bulbs, which resemble round, fleshy stem modifications, for storage. Rhizomes grow horizontally underground, but may produce vertical shoots. Corms are modified stems that resemble rhizomes, but are thicker and more rounded. Corms serve as food storage for plants and ensure their survival through harsh winter conditions.