What is a group of closely related species called?

Answer 1

It depends on the usage. A lot of closely related species will belong to the same genus. For common usage however, i.e. to say Chimpanzees and Gorrilas are closely related would make them a family rather than the same genus.

There are a number of other phrases. The word clade is commonly used. A clade refers to animals sharing common ancestors. Using the example as before, Chimpanzees and Gorillas are close relatives where humans are considered vastly different (or not very in the grand scheme of taxonomy). They would however belong to the same clade, as would monkeys.

For very, very closely related species, the phrase Species Complex is often used. These are species that are very very similar, often to the point of appearing identical, but being sufficiently genetically different to fulfill the criteria for separate species, i.e. they won't mate, or if they do, their offspring are not completely viable. Common examples include fruitflies within the Drosophila melanogaster complex and mosquitoes in the Anopheles gambiae.