Tree of Life Glossary

clade:

a monophyletic group of organisms; a single complete branch of the Tree of Life.

dichotomous:

having all branching points on the tree being dichotomies. That is, a tree is dichotomous if at each branch point there are only two descendents. This is in contrast to a polytomous tree.

dichotomy:

A branch point on a tree that has two descendents.

monophyletic:

A group of organisms that includes their most recent common ancestor and all of its descendents.

paraphyletic:

A group of organisms that includes their most recent common ancestor and some but not all of its descendents. (Technically speaking, the distinction between polyphyletic and paraphyletic is not as clear as it might seem.)

phylogeny:

The evolutionary tree connecting a group of organisms. Any group of species are descended from a common ancestral species, which, over time, split into two species, with these descendents splitting again, and so on, until the entire collection of species was produced. The genealogical connections thereby formed in general take the shape of a tree, called the phylogeny of the group.

polyphyletic:

A group of organisms that does not include their most recent common ancestor. (Technically speaking, the distinction between polyphyletic and paraphyletic is not as clear as it might seem.)

polytomous:

having at least one branch point on the tree that is a polytomy. A tree with only one polytomy is called polytomous, as is a tree with multiple polytomies. This is in contrast to a dichotomous tree.

polytomy:

A branch point on a tree that has more than two descendents.

root:

The root of a piece of the Tree of Life is that branch that connects to remander of the Tree; that is, it is the branch that connects to the enclosing clade.

terminal taxa:

The taxa or named groups at the tips of the branches of a tree.