Wastebasket taxon (also called a
wastebin taxon,
dustbin taxon or
catch-all taxon) is a term used in some
taxonomic circles to refer to a
taxon that has the sole purpose of classifying organisms that do not fit anywhere else. They are typically defined by either their designated members' often superficial similarity to each other, or their
lack of one or more distinct
character states or by their
not belonging to one or more other taxa. Wastebasket taxa are by definition either
paraphyletic or
polyphyletic, and are therefore not considered to be valid taxa under strict cladistic rules of taxonomy. The name of a wastebasket taxon may in some cases be retained as the designation of an
evolutionary grade, however.