Polytomy

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A polytomy (also called a polychotomy) is a section of a phylogeny in which the evolutionary relationships can not be fully resolved to dichotomies.

In a phylogenetic tree, a polytomy is represented as a node which has more than two immediate descending branches. Two types of polytomies are recognised, soft and hard polytomies. Soft polytomies are a biological nuisance and are the result of insufficient information. To the contrary, hard polytomies represents an event in which an ancestor gave rise to more than two daughter species at the same time. An example of the latter is the Drosophila simulans species complex.