Which level of taxa is used to describe a group of closely related species?

The appropriate level of taxa used to describe a group of closely related species is the genus. The genus is a classification that groups together species that share a common ancestor and exhibit similar characteristics. Species within a genus are often so closely related that they can interbreed and produce fertile offspring.

For instance, in the genus Panthera, which includes lions, tigers, leopards, and jaguars, these species share many traits and are more closely related to each other than to species in different genera. This taxonomic rank is crucial in biology for organizing the diversity of life and understanding the evolutionary relationships among species.

The other levels mentioned, such as family, order, and phylum, represent broader categories that group together multiple genera or larger aggregates of organisms, therefore making them less specific for describing closely related species.