Tree of Life

The Tree of Life

This version of the Tree of Life from Appendix A of the textbook has been linked to the online database at DiscoverLife.org. By clicking any group name on the tree, you can quickly access a wealth of information and images related to that group, such as photos, distribution maps, species lists, and identification keys. Click the link above to open the Tree in a new browser window.

About the Tree of Life

Phylogeny is the organizing principle of modern biological taxonomy. A guiding principle of modern phylogeny is monophyly. A monophyletic group is considered to be one that contains an ancestral lineage and all of its descendants. Any such group can be extracted from a phylogenetic tree with a single cut.

The trees shown here provide a guide to the relationships among the major groups of extant (living) organisms in the tree of life as we have presented them throughout this book. The position of the branching “splits” indicates the relative branching order of the lineages of life, but the time scale is not meant to be uniform. In addition, the groups appearing at the branch tips do not necessarily carry equal phylogenetic “weight.” For example, the ginkgo is indeed at the apex of its lineage; this gymnosperm group consists of a single living species. In contrast, a phylogeny of the eudicots could continue on from this point to fill many more trees the size of this one.

The descriptions given for each group are informal descriptions of some major features of the organisms described in Part Four of this book. Each entry gives the group’s common name, followed by the formal scientific name of the group (in parentheses). Numbers in square brackets reference the location of the respective groups on the tree.

It is sometimes convenient to use an informal name to refer to a collection of organisms that are not monophyletic but nonetheless all share (or all lack) some common attribute. We call these “convenience terms”; such groups are indicated in these entries by quotation marks, and we do not give them formal scientific names. Examples include “prokaryotes,” “protists,” and “algae.” Note that these groups cannot be removed with a single cut; they represent a collection of distantly related groups that appear in different parts of the tree. We also use quotation marks here to designate two groups of fungi that are not believed to be monophyletic.