Form taxon

classification of organisms based on their morphology

A form taxon is a group of organisms on based on what they look like (their morphology). Such a taxon may not reflect their biological relationships. In other words, they may not be a clade.

A good example are the terms snake and lizard, which are not good taxonomic terms because neither is a proper clade. On the other hand, all poisonous snakes and lizards are in a good clade, the Toxicofera.[1]

Another good example are ducks. They are in the same family as swans and geese, but called "ducks" because of what they look like.


  1. Reeder, Tod W. et al 2015. Integrated analyses resolve conflicts over squamate reptile phylogeny and reveal unexpected placements for fossil taxa. PLoS ONE. 10 (3): e0118199. [1]