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In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.

A basal group forms an outgroup to the rest of the clade, such as in the following example:

	Basal group
	Non-basal group Non-basal group Non-basal group Non-basal group

The word "basal" is preferred to the term "primitive", which may carry false connotations of inferiority or a lack of complexity.

The term basal can only be correctly applied to clades of organisms, not to individual traits possessed by the organisms—although it can be misused in this manner in technical literature. While the term "basal" applies to clades, characters or traits are usually considered derived if they are absent in a basal group, but present in other groups. This assumption only holds true if the basal group is a good analogy for the last common ancestor of the group.

As an example, the angiosperm plant family, the Amborellaceae is considered the most basal of extant angiosperms.

	Amborellales Monocots Magnoliids Eudicots

In animal family Hominidae, the gorillas are an outgroup to chimpanzees and humans. These three organisms, gorillas, chimpanzees, and humans form a clade, the subfamily Homininae, of which gorillas are the basal member.

	Humans Chimpanzees Gorillas

However, in the family Hominidae, the orangutans form an outgroup to the subfamily Homininae, the clade to which gorillas, chimpanzees, and humans all belong.

	Humans Chimpanzees Gorillas Orangutans

[edit] References

• Budd, Graham E.; Jensen, Sören (2000). "A critical reappraisal of the fossil record of the bilaterian phyla". Biological Reviews (Cambridge University Press) 75 (2): 253. doi:10.1017/S000632310000548X.