[A]ll living things fall into […] three great domains. The Domain Bacteria includes Cyanobacteria and most groups commonly called bacteria. The Domain Archaea (‘ancient ones’) comprises the Halobacteria (salt-digesters), Methanobacteria (methane-producers), Eocytes (heat-loving sulphur-metabolizing bacteria), and others. The Domain Eucarya includes an array of single-celled forms that are often lumped together as ‘algae’, as well as multicellular organisms. Perhaps the most startling observation is that, within Eucarya, the fungi are more closely related to the animals than to the plants, and this has been confirmed in several analyses. This poses a moral dilemma for vegetarians: should they eat mushrooms or not.
Michael Benton, The History of Life: A Very Short Introduction, New York, 2008, pp. 35-36