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Symplesiomorphy (noun)
An taxa.
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Plesiomorphy (noun)
A character state that is present in both outgroups and in the ancestors
Wiktionary
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Symplesiomorphy (noun)
The possession by two or more organisms or taxa of a shared primitive or ancestral character not exclusive to or characteristic of them in particular; the shared character itself.
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Plesiomorphy (noun)
The state of being plesiomorphic; ancestral or primitive condition as compared to a later, derived character state. Also (as a count noun): an ancestral or plesiomorphic feature or trait.
Oxford Dictionary