Ginger is a modification of which part of the plant?

A stem is the plant part marked by nodes (points bearing leaves and buds) and internodes. Roots never form nodes, buds, or leaves; leaves are flattened organs whose job is photosynthesis; a fruit develops only after fertilization of a flower's ovary. Crucially, a stem can grow underground and still be identified as a stem purely from this node-internode-bud anatomy — such underground stems are called rhizomes.

Ginger (Zingiber officinale) grows as a thick, horizontal underground structure called a rhizome. Even though it lies below the soil the way a root would, it shows the defining stem anatomy: nodes bearing scale-like leaves, buds at the nodes, and new aerial shoots arising from those buds. Since roots never carry nodes or buds, this anatomy places ginger's underground part in the stem category.

• Root: true roots absorb water and minerals and never carry nodes or buds — ginger's underground structure carries both, ruling out the root option.

• Leaf: leaves are flattened photosynthetic organs attached at stem nodes — ginger's underground structure is the axis itself, not an organ attached to it.

• Fruit: a fruit forms only after fertilization of a flower's ovary — ginger propagates from its underground growth, with no floral or fertilization origin involved.

So ginger's underground growth is classified as a modified stem (a rhizome).