Tree of Life

Glossary of Key Terms

Term

Definition

• Amoebozoa

A "Supergroup" in modern biology that contains organisms like Slime Moulds. Referred to as Kingdom Protista for simplification purposes.

• Angiosperms

Flowering plants that produce seeds enclosed within a fruit or flower. Formally classified as the Phylum (or Division) Anthophyta.

• Animalia

The kingdom of multicellular eaters, including birds, mammals, insects, and arachnids.

• Archaea

One of the three primary domains of life. These are single-celled organisms that lack a nucleus but are genetically distinct from bacteria and whose internal machinery is more similar to Eukarya. They are often extremophiles.

• Arthropoda

A formal phylum in the Animalia kingdom for organisms with a segmented body, an exoskeleton, and jointed legs. It is the largest phylum on Earth, containing insects, spiders, and crabs.

• Asteraceae

The "Daisy" family of plants, characterised by their composite flower heads.

• Bacteria

One of the three primary domains of life. They are single-celled organisms that lack a nucleus and are considered the oldest lineage on the tree.

• Chordata

The phylum for animals that have a backbone or a spinal cord (notochord). This group includes humans, sharks, birds, and reptiles.

• Cladistics

A modern approach to biological classification that groups organisms based strictly on their DNA and common ancestors rather than only physical similarities.

• Class

The taxonomic rank below Phylum and above Order, grouping organisms based on a more specific "lifestyle" or "grade of organisation," such as Mammalia or Insecta.

• Cryptogams

An informal, retired classification for any plant-like organism that reproduces by spores rather than seeds. It is no longer used formally because it grouped unrelated organisms from different kingdoms.

• Domain

The highest and broadest level of the modern taxonomic hierarchy. The three domains are Bacteria, Archaea, and Eukarya.

• Eudicots

Meaning "True Dicots," a modern classification based on genetic evidence for the vast majority of plants that were traditionally called "dicots."

• Eukarya

The domain of life that includes every organism with a nucleus in its cells. It is divided into four kingdoms: Animals, Plants, Fungi, and Protists.

• Family

The taxonomic rank below Order and above Genus.

• Fungi

The kingdom of absorptive feeders with cell walls made of chitin. This group includes mushrooms and lichens.

• Genus

The taxonomic rank below Family and above Species. It forms the first part of an organism's two-part scientific name (e.g., Homo in Homo sapiens).

• Horizontal Gene Transfer

A process, common in bacteria, where genetic material is transferred between organisms that are not parent and offspring. This causes some scientists to view the Tree of Life as more of a "Web of Life."

• Hybrid

The offspring resulting from a cross between two different species, such as a mule (donkey and horse). Hybrids are typically sterile and considered "dead ends" on the tree.

• Kingdom

The taxonomic rank below Domain. Well-known kingdoms include Animalia, Plantae, and Fungi.

• LUCA

The Last Universal Common Ancestor; a single-celled organism from which all life on Earth descended, estimated to have lived 3.5 to 3.8 billion years ago.

• Monera

A historical kingdom that once contained all known bacteria. This name has been largely retired by modern science, as the organisms are now split across the Bacteria and Archaea domains.

• Order

The taxonomic rank below Class and above Family. Organisms in an order often share specific biological "inventions," such as the wing structure in insect orders or specialised teeth in mammalian orders.

• Phylogenetic Tree

The scientific term for the Tree of Life; a diagram showing the evolutionary relationships and common ancestry of all living organisms.

• Phylum

The taxonomic rank below Kingdom and above Class, used to group organisms based on their general body plan (e.g., having a backbone or an exoskeleton).

• Plantae

The kingdom of photosynthetic organisms, including flowers, mosses, ferns, and trees.

• Prokaryotes

A term from an older classification system for single-celled organisms without a nucleus, which included both Bacteria and Archaea. This has been replaced by the three-Domain system.

• Protista

A historical kingdom for eukaryotic organisms that did not fit into the Animal, Plant, or Fungi kingdoms. It is now considered an unstable "junk drawer" category.

• Species

The most specific major rank in the taxonomic hierarchy. It forms the second part of the scientific name and is often defined as a group of organisms that can interbreed and produce fertile offspring.

• Subspecies

A rank below species used for a geographically isolated population that has developed distinct characteristics but can still interbreed with other populations of the same species. It is indicated by a third word in the scientific name.

• Taxonomy

The scientific field of naming, defining, and classifying groups of biological organisms on the basis of shared characteristics.

• Tetrapods

A Superclass or Clade within Phylum Chordata meaning "four-footed." It includes all animals that evolved from ancestors with four limbs, including amphibians, reptiles, birds, and mammals.

• Tribe

An intermediary taxonomic rank that sits between Subfamily and Genus, used to group very closely related genera within large families.