Which type of root system is characterized by a single main root extending downward?

The type of root system characterized by a single main root extending downward is known as a taproot system. In this system, a single primary root grows deep into the soil, providing stability and access to deeper water and nutrients. This main root can develop smaller lateral roots branching off from it.

Taproots are typically seen in many plants such as carrots, radishes, and dandelions. They are advantageous in environments where the topsoil may be dry, as the deep taproot can reach moisture that shallower roots cannot access. This deep root structure also helps anchor the plant firmly, making it more resilient against environmental stresses.

In contrast, the fibrous root system consists of many thin roots of similar length, which spread out horizontally, providing a larger surface area for moisture and nutrient absorption but generally lacking the depth of a taproot. Adventitious roots arise from non-root tissues, such as stems or leaves, and can also perform functions like anchoring and support, but they do not form a dominant main root as seen in taproots. The term "nomadic root" does not refer to a recognized root system in botany and could be considered a distractor.