Which classification grouping consists of closely related species?

The classification grouping that consists of closely related species is the genus. In biological taxonomy, a genus is a rank in the hierarchy that groups species that share common characteristics and are closely related to one another. For example, the genus Panthera includes species such as the lion and the tiger, which are more closely related to each other than to species in other genera.

In contrast, species represents the most specific level of classification and refers to individual organisms that can interbreed and produce fertile offspring. While it identifies a single type of organism, it does not encompass closely related species like a genus does.

Order and phylum are higher taxonomic categories that encompass broader groups of organisms. An order consists of multiple families, which in turn contain various genera, while a phylum groups together several classes of organisms based on certain fundamental characteristics. Therefore, the genus is the correct choice as it effectively captures the idea of closely related species within taxonomy.