Which type of root grows vertically downward and can develop subsidiary rootlets?

The tap root is characterized by its main root growing vertically downward and being thicker compared to other types of roots. This design allows for deeper anchorage in the soil, making it particularly effective in accessing deeper water supplies and nutrients. The tap root system typically develops subsidiary rootlets that branch off from the main root. These rootlets enhance the plant's ability to absorb water and nutrients, providing a stable foundation and support for the plant structure above ground.

In contrast, fibrous roots primarily spread out horizontally with numerous thin roots that emerge from the base of the plant, rather than developing a strong central root. Adventitious roots arise from unusual places, such as stems or leaves, and do not typically manifest the same downward growth pattern associated with tap roots. The radicle refers specifically to the embryonic root that emerges first during seed germination; it does not develop into a fully functional root system like a tap root does as the plant matures. Thus, the unique downward growth and formation of subsidiary rootlets clearly define the tap root's role in plant establishment and nutrient acquisition.