Delphinidin

When a seed germinates, the tiny, rootlike radicle, a part of the embryo (immature plantlet) within it, grows out and develops into the first root. The radicle may develop into a thick, tapered taproot, from which thinner branch roots arise, or many adventitious roots may arise from the stem, which is attached to the radicle and continuous with it. Adventitious roots are those that do not develop from another root but develop instead from a stem or leaf. A fibrous root system, which may have large numbers of fine roots of similar diameter, then develops from the adventitious roots. Many mature plants have a combination of taproot and fibrous root systems.

The number of roots produced by a single plant may be prodigious. For example, a single, mature ryegrass plant may have as many as 15 million individual roots and branch roots, with a combined length of 644 kilometers (400 miles) and a total surface area larger than a volleyball court, all contained within 0.57 cubic meter (20 cubic feet) of soil. Root hairs greatly increase the total surface area of the root. Many plants such as peas and carrots, whose seeds have two “seed leaves”—commonly referred to as dicots—have taproot systems with one, or occasionally more, primary roots from which secondary roots develop.

Monocotyledonous plants (e.g., corn and rice, whose seeds have one “seed leaf”—commonly referred to as monocots), on the other hand, have fibrous root systems. Adventitious and other types of roots may develop in both dicots and monocots. In English and other ivies, lateral adventitious roots that aid in climbing appear along the aerial stems, and in certain plants with specialized stems (e.g., rhizomes, corms, and bulbs), adventitious roots are the only kind produced.