monofiletic

Monofiletic is a less common spelling used in some texts to denote what is more widely called monophyletic. In English, monophyletic is the standard term for a group that includes an ancestor and all of its descendants.

A monofiletic (monophyletic) group is defined as a clade that stems from a single common ancestor and contains every lineage descended from that ancestor. This contrasts with paraphyletic groups, which include the common ancestor and some, but not all, descendants, and with polyphyletic groups, which do not include the most recent common ancestor of all members.

Determining whether a group is monofiletic involves phylogenetic analysis using morphological characters, molecular data, or both. Researchers aim to identify synapomorphies—shared derived traits—that diagnose a clade. Robust support often comes from multiple data sources and statistical methods, producing cladograms that reflect hypothesized evolutionary relationships.

In taxonomy, recognizing monofiletic groups is desirable because such groups reflect patterns of descent and common ancestry. Traditional classifications have sometimes treated large groups as paraphyletic or polyphyletic; modern cladistic approaches increasingly favor reorganizing groups to restore monophyly. For example, Mammalia is widely regarded as monophyletic, comprising all descendants of the most recent common ancestor of mammals. Some historical schemes treated reptiles as a single group, which would be paraphyletic unless birds are included.

Related concepts include monophyly, cladistics, and phylogeny. The term monofiletic remains a synonym of monophyletic in some sources, though monophyletic is the preferred form in contemporary English usage.