ADAPTIVE RADIATION The rapid diversification of a group of species into various habitats over a relatively short period of geological time. However, the term is often used as a synonym for any large monophyletic group of taxa.

ANGIOSPERMS Flowering vascular plants that form seeds inside an ovary.

ARTIODACTYLS Hoofed animals with an even number of digits. They belong to the mammalian Order Artiodactyla and include animals such as cattle, deer and pigs.

ASCOMYCOTA The largest phylum of fungi; also called ascomycetes or 'sac fungi'. They produce sexual spores in specialized sac-like cells called asci.

BAYESIAN METHOD A method that selects the tree that has the greatest posterior probability (probability that the tree is correct), under a specific model of substitution.

BOOTSTRAP METHOD As applied to molecular phylogenies. Nucleotide or amino-acid sites are sampled randomly, with replacement, and a new tree is constructed. This is repeated many times and the frequency of appearance of a particular node among the bootstrap trees is viewed as a support (confidence) value for deciding on the significance of that node.

BRYOPHYTES A term that refers traditionally to non-vascular land plants, nearly all of which are quite small (1–2 cm high). Bryophytes include hornworts, liverworts and mosses; however, the term might also be used in a more restricted sense to refer to the mosses alone (Division: Bryophyta).

CAMBRIAN EXPLOSION The sudden appearance, approx520 million years ago, of many major groups (phyla) of animals, as witnessed in the fossil record.

CENOZOIC The geological time period (era) that spans from 65 million years ago to the present day.

COELOM The body cavity of an animal, such as a vertebrate or insect, which is completely lined with mesodermal cells.

CYANOBACTERIA A phylum of Eubacteria, formerly known as the "blue-green algae". These prokaryotes are the only organisms known to be capable of oxygenic photosynthesis.

ELONGATION FACTOR 1 An enzyme that functions in the process of protein translation.

EUDICOTS The largest clade of angiosperms, characterized by two cotyledons (seed leaves) and three symmetrically placed pollen apertures or aperture arrangements that are derived from this.

GLAUCOCYSTOPHYTES A small group of freshwater algae, also called 'glaucophytes'. Species in this group have plastids with a peptidoglycan cell wall (peptidoglycan is the main component of bacterial cell walls).

GYMNOSPERMS Non-flowering vascular plants with naked seeds that are not enclosed in an ovary (for example, pine).

HORIZONTAL TRANSFER The transfer of genetic material between the genomes of two organisms, which are usually different species.

HORNWORTS A group of small, non-vascular plants (Division: Anthocerotophyta) that are distinguished by their tall horn-like sporophyte (diploid generation) that grows on the more flattened gametophyte (haploid generation). They usually have a single, large chloroplast in each cell.

LIVERWORTS A group of small, mat-like, non-vascular plants (Division: Marchantiophyta) that occur in diverse habitats but most commonly on the forest floor. Some species have lobe-shaped leaves that resemble a liver.

LOCAL-CLOCK METHOD A method for estimating divergence time by accounting for differences in the rate of substitution among lineages (branches) in a tree.

MAXIMUM LIKELIHOOD A method that selects the tree that has the highest probability of explaining the sequence data, under a specific model of substitution (changes in the nucleotide or amino-acid sequence).

MAXIMUM PARSIMONY A method that selects the tree that requires the fewest number of substitutions.

MONOCOTS (Monocotyledonous plants). Flowering plants with one cotyledon (or seed leaf).

MONOPHYLETIC Includes all the descendants of a single common ancestor.

NEIGHBOUR JOINING A method that selects the tree that has the shortest overall length (sum of all branch lengths).

PARAPHYLETIC Includes some, but not all, of the descendants of a single common ancestor.

PRECAMBRIAN An informal geological time period that spans from the time the Earth was born, approx4,500 million years ago (Mya), until approx545 Mya.

PSEUDOCOELOM Literally 'false cavity'; the body cavity of an animal, such as a nematode, that is not fully lined with mesodermal cells.

PYRENOMYCETES The largest subgroup of ascomycotan fungi, which are characterized by flask-shaped fruiting bodies.

RELATIVE RATE TESTS Statistical tests that determine, at a given level of stringency, whether two or more branches in a tree have evolved at the same rate of sequence change.

SPIROCHAETES A phylum of Eubacteria that has a spiral or corkscrew-like appearance and axial filaments (similar to flagella). These prokaryotes are responsible for human diseases, such as Lyme disease and syphilis.

TAXON SAMPLING A term that indicates that the branching pattern of a tree might be influenced by the number or type of taxa (for example, species) included.