| Term | Definition |
|---|
| apomorphy | derived character state (cf. plesiomorphy) |
| autapomorphy | derived character state that is restricted to a single terminal taxon in a data set. may be synapomorphy at a less-inclusive level. one type of uninformative character. |
| clade | monophyletic group, made up of an ancestor and all of its descendents |
| cladogram | branching diagram that shows hypothesized phylogenetic (sister-group) relationships of a group of organisms. does not illustrate degree of divergence, only hierarchical pattern. |
| homology, homologue | similarity due to inheritance of a feature from a common ancestor. synapomorphies are homologs. |
| homoplasy, homoplasious, homoplastic | similarity due to parallelism or reversal of character states |
| ingroup | group under investigation in cladistic analysis to determine phylogenetic pattern |
| monophyly, monophyletic group | group that includes a most recent common ancestor plus all and only all of its descendants, and is diagnosed by synapomorphies |
| outgroup | taxon used in cladistic analysis for comparative purposes, usually to enable character polarity |
| outgroup comparison | indirect method of character polarization that uses information on character states in outgroup taxa to determine relative apomorphy and plesiomoprhy of character states found in ingroup taxa |
| paraphyly, polyphyletic group | group with two or more ancestors, but not including true common ancestor of its members. based on convergent (homoplastic) characters |
| symplesiomorpy | shared ancestral character state. paraphyletic groups may result from mistaking symplesiomorphies for synapomorphies. can also be a type of uninformative character (if shared by all members of study-group). |
| synapomorphy | shared derived character state. used to define monophyletic groups. |
| uninformative character | one that is not useful in constructing hypotheses of phylogenetic relationships (autapomorphy, symplesiomorphy) |
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