Animals Total numbers are estimates; figures from different authors vary wildly, not least because some are based on described species, and some on extrapolations to numbers of undescribed species. For instance, around 25,000–27,000 species of nematodes have been described, while published estimates of the total number of nematode species include 10,000–20,000; 500,000; 10 million; and 100 million.
Plants The kingdom Plantae is defined in various ways by different biologists (see
Current definitions of Plantae). All definitions include the living
embryophytes (land plants), to which may be added the two green algae divisions,
Chlorophyta and
Charophyta, to form the clade
Viridiplantae. The table below follows the influential (though contentious)
Cavalier-Smith system in equating "Plantae" with
Archaeplastida, a group containing Viridiplantae and the algal
Rhodophyta and
Glaucophyta divisions. The definition and classification of plants at the division level also varies from source to source, and has changed progressively in recent years. Thus some sources place horsetails in division
Arthrophyta and ferns in division
Monilophyta, while others place them both in Monilophyta, as shown below. The division
Pinophyta may be used for all
gymnosperms (i.e. including cycads, ginkgos and gnetophytes), or for conifers alone as below. Since the first publication of the
APG system in 1998, which proposed a classification of
angiosperms up to the level of
orders, many sources have preferred to treat ranks higher than orders as informal clades. Where formal ranks have been provided, the traditional divisions listed below have been reduced to a very much lower level, e.g.
subclasses.
Fungi Phylum Microsporidia is generally included in kingdom Fungi, though its exact relations remain uncertain, and it is considered a
protozoan by the International Society of Protistologists which is considered undesirable by many biologists. Accordingly, there is a proposal to abolish the Zygomycota phylum. Its members would be divided between phylum Glomeromycota and four new subphyla
incertae sedis (of uncertain placement):
Entomophthoromycotina,
Kickxellomycotina,
Mucoromycotina, and
Zoopagomycotina. which is less acceptable to present-day biologists than in the past. Proposals have been made to divide it among several new kingdoms, such as
Protozoa and
Chromista in the
Cavalier-Smith system. Protist taxonomy has long been unstable, with different approaches and definitions resulting in many competing classification schemes. Many of the phyla listed below are used by the
Catalogue of Life, and correspond to the Protozoa-Chromista scheme, with updates from the latest (2022) publication by
Cavalier-Smith. Other phyla are used commonly by other authors, and are adapted from the system used by the International Society of Protistologists (ISP). Some of the descriptions are based on the 2019 revision of eukaryotes by the ISP. The number of protist phyla varies greatly from one classification to the next. The Catalogue of Life includes
Rhodophyta and
Glaucophyta in kingdom Plantae, In addition, less popular classification schemes unite
Ochrophyta and
Pseudofungi under one phylum,
Gyrista, and all alveolates except
ciliates in one phylum
Myzozoa, later lowered in rank and included in a paraphyletic phylum
Miozoa. •
Abditibacteriota •
Acidobacteriota, phenotypically diverse and mostly uncultured •
Actinomycetota, High-G+C Gram positive species •
Aquificota, deep-branching •
Armatimonadota •
Atribacterota •
Bacillota, Low-G+C Gram positive species, such as the spore-formers
Bacilli (aerobic) and
Clostridia (anaerobic) •
Bacteroidota •
Balneolota •
Bdellovibrionota •
Caldisericota, formerly candidate division OP5,
Caldisericum exile is the sole representative •
Calditrichota •
Campylobacterota •
Chlamydiota •
Chlorobiota, green sulphur bacteria •
Chloroflexota, green non-sulphur bacteria •
Chrysiogenota, only 3 genera (
Chrysiogenes arsenatis,
Desulfurispira natronophila,
Desulfurispirillum alkaliphilum) •
Coprothermobacterota •
Deferribacterota •
Deinococcota,
Deinococcus radiodurans and
Thermus aquaticus are "commonly known" species of this phyla •
Dictyoglomota •
Elusimicrobiota, formerly candidate division Thermite Group 1 •
Fibrobacterota •
Fusobacteriota •
Gemmatimonadota •
Ignavibacteriota •
Kiritimatiellota •
Lentisphaerota, formerly clade VadinBE97 •
Mycoplasmatota, notable genus:
Mycoplasma •
Myxococcota •
Nitrospinota •
Nitrospirota •
Planctomycetota •
Pseudomonadota, the most well-known phylum, containing species such as
Escherichia coli or
Pseudomonas aeruginosa •
Rhodothermota •
Spirochaetota, species include
Borrelia burgdorferi, which causes Lyme disease •
Synergistota •
Thermodesulfobacteriota •
Thermomicrobiota •
Thermotogota, deep-branching •
Verrucomicrobiota Archaea Currently there are 2 phyla that have been validly published according to the
Bacteriological Code •
Nitrososphaerota •
Thermoproteota, second most common archaeal phylum Other phyla that have been proposed, but not validly named, include: • "
Euryarchaeota", most common archaeal phylum • "
Korarchaeota" • "
Nanoarchaeota", ultra-small symbiotes, single known species == See also ==