knollen

Knollen is the German term for tubers, which are swollen underground storage organs formed by certain plants. They function mainly to store nutrients such as starch and sugars, helping the plant survive unfavorable seasons and to regrow after dormancy. In botanical use, knollen can originate from thickened stems (stem tubers) or from thickened roots (root tubers).

A stem tuber typically forms on a runner or stolon and often bears buds or “eyes” that can sprout into new shoots. A root tuber develops directly from a root and generally lacks a distinct stem segment. This distinction can be important for propagation and cultivation, as stem tubers and root tubers may require different handling.

The best-known example is the potato (Solanum tuberosum), a stem tuber that forms on subterranean stolons and bears eyes that sprout into new plants. Other cultivated knollen include tubers of ornamental plants such as dahlias, which are also stem-based tubers. Some plant species form root tubers rather than stem tubers, and in culinary and horticultural contexts these distinctions can influence growing practices and terminology.

Knollen differ from bulbs, which are layered storage organs derived mainly from leaves, and from rhizomes, which are horizontal underground stems that store reserves and enable vegetative spread. In cultivation and research, knollen are commonly used for propagation by planting pieces that contain at least one bud or eye.

Etymology: the word knolle comes from German, meaning a rounded lump, with knollen serving as the plural term. The word is used broadly to describe storage organs that resemble lumps or bulbs.