Tree of LifeDomains, Kingdoms and Phyla Explained
How is life on Earth classified? This page covers the domains, kingdoms and phyla on the game's Tree of Life and how they nest inside one another.
All life on Earth descends from one ancestor, so it can be drawn as a tree. The root is the last universal common ancestor. From it come three domains: Bacteria, Archaea and Eukaryota. Eukaryota splits into five kingdoms, and each domain or kingdom holds a set of phyla. This page covers the "trunk" of the game's Tree of Life, the top three layers: domains, kingdoms and phyla. It does not go down to classes, orders or families.
The three-domain split was a real rewrite of biology. People used to sort life into bacteria and everything else. Comparing ribosomal RNA showed that "bacteria" were really two very different kinds of life, and archaea became their own branch (Woese & Fox, PNAS 1977). The Tree of Life was then redrawn with three domains: Bacteria, Archaea and Eukaryota (Woese, Kandler & Wheelis, PNAS 1990).
The root: the last universal common ancestor
The last universal common ancestor (LUCA) is the root. Working backward from modern genes, it may have lived near hot, oxygen-free, hydrogen-rich deep-sea vents (Weiss et al., Nature Microbiology 2016). Every domain on the tree descends from it.
The three domains
| Domain | Latin name | Number of phyla |
|---|---|---|
| Bacteria | Bacteria | Nine phyla |
| Archaea | Archaea | Four phyla |
| Eukaryota | Eukaryota | Five kingdoms, each with several phyla |
The nine bacterial phyla
The nine phyla in Bacteria are: Cyanobacteria, Pseudomonadota (Proteobacteria), Bacillota (Firmicutes), Actinobacteria, Bacteroidetes, Spirochetes, Deinococcota, Aquificota and Thermotogota.
The four archaeal phyla
- Methanobacteriota (Euryarchaeota)
- Thermoproteota (Crenarchaeota)
- Nitrososphaerota (Thaumarchaeota)
- Asgard archaea
The Asgard archaea sit in an interesting spot. Lokiarchaeum, found in deep-sea sediment, carries many genes once thought to belong only to eukaryotes (Spang et al., Nature 2015). That suggests eukaryotes are unusually close relatives of archaea.
The five eukaryote kingdoms
In the game, Eukaryota is divided into five kingdoms, each with its own set of phyla.
| Kingdom | Phyla |
|---|---|
| Protozoa | Euglenozoa, Amoebozoa, Choanozoa |
| Chromista | Ochrophyta, Ciliates, Foraminifera, Haptophytes, Apicomplexa, Dinoflagellates |
| Plants | Red algae, Green algae, Stoneworts, Bryophytes, Pteridophytes, Gymnosperms, Angiosperms |
| Fungi | Chytrids, Glomeromycota, Sac fungi, Club fungi |
| Animals | Sponges, Cnidarians, Comb jellies, Flatworms, Roundworms, Rotifers, Tardigrades, Annelids, Mollusks, Brachiopods, Arthropods, Echinoderms, Chordates |
Animals have the most phyla, thirteen. The Plants row, running from red and green algae to angiosperms, nearly traces the route plants took onto land: stoneworts come first, then bryophytes, and after them pteridophytes, gymnosperms and angiosperms.
Counting the tree
Add up the phyla across the three domains: nine in Bacteria, four in Archaea, and thirty-three across the five eukaryote kingdoms, for forty-six phyla in all. Animals have the most (thirteen), followed by Plants (seven), Chromista (six), Fungi (four) and Protozoa (three). The tree is drawn only down to the phylum level, so finer classification does not appear. It has one root and three domains, and it branches more finely at each step upward.
A key event on the tree
- Endosymbiosis: mitochondria and chloroplasts were once free-living bacteria. After being swallowed, they became part of the cell. When the idea was proposed, more than a dozen journals rejected it (Margulis, published as Sagan, Journal of Theoretical Biology 1967).
Papers to search for
- Woese & Fox (1977): "Phylogenetic structure of the prokaryotic domain: The primary kingdoms"
- Woese et al. (1990): "Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya"
- Spang et al. (2015): "Complex archaea that bridge the gap between prokaryotes and eukaryotes"
- Weiss et al. (2016): "The physiology and habitat of the last universal common ancestor"
Real basis
Bacteria: a domain on the tree of life, descended from the last common ancestor.
Cyanobacteria (Cyanobacteriota): a phylum on the tree of life, under the domain Bacteria.
Proteobacteria (Pseudomonadota): a phylum on the tree of life, under the domain Bacteria.
Firmicutes (Bacillota): a phylum on the tree of life, under the domain Bacteria.
Actinobacteria (Actinomycetota): a phylum on the tree of life, under the domain Bacteria.
Bacteroidetes (Bacteroidota): a phylum on the tree of life, under the domain Bacteria.
Spirochetes (Spirochaetota): a phylum on the tree of life, under the domain Bacteria.
Deinococcota: a phylum on the tree of life, under the domain Bacteria.
Aquificota: a phylum on the tree of life, under the domain Bacteria.
Thermotogota: a phylum on the tree of life, under the domain Bacteria.
Archaea: a domain on the tree of life, descended from the last common ancestor.
Euryarchaeota (Methanobacteriota): a phylum on the tree of life, under the domain Archaea.
Crenarchaeota (Thermoproteota): a phylum on the tree of life, under the domain Archaea.
Thaumarchaeota (Nitrososphaerota): a phylum on the tree of life, under the domain Archaea.
Asgardarchaeota: a phylum on the tree of life, under the domain Archaea.
Eukaryota: a domain on the tree of life, descended from the last common ancestor.
Protozoa: a kingdom on the tree of life, under the domain Eukaryota.
Euglenozoa: a phylum on the tree of life, under the kingdom Protozoa.
Amoebozoa: a phylum on the tree of life, under the kingdom Protozoa.
Choanozoa: a phylum on the tree of life, under the kingdom Protozoa.
Chromista: a kingdom on the tree of life, under the domain Eukaryota.
Ochrophyta: a phylum on the tree of life, under the kingdom Chromista.
Ciliates (Ciliophora): a phylum on the tree of life, under the kingdom Chromista.
Foraminifera: a phylum on the tree of life, under the kingdom Chromista.
Haptophytes (Haptophyta): a phylum on the tree of life, under the kingdom Chromista.
Apicomplexa: a phylum on the tree of life, under the kingdom Chromista.
Dinoflagellates (Dinoflagellata): a phylum on the tree of life, under the kingdom Chromista.
Plants (Plantae): a kingdom on the tree of life, under the domain Eukaryota.
Red algae (Rhodophyta): a phylum on the tree of life, under the kingdom Plants.
Green algae (Chlorophyta): a phylum on the tree of life, under the kingdom Plants.
Stoneworts (Charophyta): a phylum on the tree of life, under the kingdom Plants.
Bryophytes (Bryophyta): a phylum on the tree of life, under the kingdom Plants.
Pteridophytes (Pteridophyta): a phylum on the tree of life, under the kingdom Plants.
Gymnosperms (Gymnospermae): a phylum on the tree of life, under the kingdom Plants.
Angiosperms (Angiospermae): a phylum on the tree of life, under the kingdom Plants.
Fungi: a kingdom on the tree of life, under the domain Eukaryota.
Chytrids (Chytridiomycota): a phylum on the tree of life, under the kingdom Fungi.
Glomeromycota: a phylum on the tree of life, under the kingdom Fungi.
Sac fungi (Ascomycota): a phylum on the tree of life, under the kingdom Fungi.
Club fungi (Basidiomycota): a phylum on the tree of life, under the kingdom Fungi.
Animals (Animalia): a kingdom on the tree of life, under the domain Eukaryota.
Sponges (Porifera): a phylum on the tree of life, under the kingdom Animals.
Cnidarians (Cnidaria): a phylum on the tree of life, under the kingdom Animals.
Comb jellies (Ctenophora): a phylum on the tree of life, under the kingdom Animals.
Flatworms (Platyhelminthes): a phylum on the tree of life, under the kingdom Animals.
Roundworms (Nematoda): a phylum on the tree of life, under the kingdom Animals.
Rotifers (Rotifera): a phylum on the tree of life, under the kingdom Animals.
Tardigrades (Tardigrada): a phylum on the Tree of Life, in the animal kingdom.
Annelids (Annelida): a phylum on the Tree of Life, in the animal kingdom.
Mollusks (Mollusca): a phylum on the Tree of Life, in the animal kingdom.
Brachiopods (Brachiopoda): a phylum on the Tree of Life, in the animal kingdom.
Arthropods (Arthropoda): a phylum on the Tree of Life, in the animal kingdom.
Echinoderms (Echinodermata): a phylum on the Tree of Life, in the animal kingdom.
Chordates (Chordata): a phylum on the Tree of Life, in the animal kingdom.
Related research
These studies relate to this topic but are not direct proof of this page.
A third kind of life: Comparing ribosomal RNA showed that “bacteria” are actually two very different kinds of life, and archaea became their own branch.
Source: Woese & Fox, PNAS 1977, "Phylogenetic structure of the prokaryotic domain: The primary kingdoms"
The three-domain system: The tree of life was redivided into three domains: Bacteria, Archaea and Eukaryotes.
Source: Woese, Kandler & Wheelis, PNAS 1990, "Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya"
Endosymbiotic theory: Margulis proposed that mitochondria and chloroplasts were once independent bacteria that were swallowed and became part of the cell. It was rejected by over a dozen journals.
Source: Sagan (Margulis), Journal of Theoretical Biology 1967, "On the origin of mitosing cells"
The home of LUCA: Working back from modern genes, the common ancestor of all life may have lived near hot, oxygen-free, hydrogen-rich deep-sea vents.
Source: Weiss et al., Nature Microbiology 2016, "The physiology and habitat of the last universal common ancestor"
Asgard archaea: Lokiarchaeota found in deep-sea sediments carry many genes once thought to exist only in eukaryotes.
Source: Spang et al., Nature 2015, "Complex archaea that bridge the gap between prokaryotes and eukaryotes"
Related open-source projects
OneZoom Tree of Life
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