What is a characteristic of the root system of sedges?

The chosen response accurately reflects the distinctive features of sedge plants. Sedges are known for having solid, triangular or three-sided stems, which is a key characteristic that differentiates them from other grass-like plants like grasses and rushes. This three-sided stem structure contributes to the plant's overall stability and can help in identifying sedges in the field.

While the other characteristics highlighted in the options may apply to different plant types, they do not accurately describe sedges. For instance, sedges do indeed have roots, contrary to the implication in the first option. Additionally, while some sedge species may have taproots, they are not universally characterized by deep taproots like some other plants. The latter option that suggests they grow in groups of three is also not a defining trait, as sedges can grow in various formations depending on the species and environmental conditions. Thus, the identification of sedges by their solid, three-sided stems is both correct and informative.