THE LIVING WORLD
Unit Four. The Evolution and Diversity of Life
Fungi are an ancient group of organisms at least 400 million years old. There are nearly 74,000 described species, in five groups (described in table 18.1), and many more awaiting discovery. Many fungi are harmful because they decay, rot, and spoil many different materials as they obtain food and because they cause serious diseases in animals and particularly in plants. Other fungi, however, are extremely useful. The manufacturing of both bread and beer depends on the biochemical activities of yeasts, single-celled fungi that produce abundant quantities of carbon dioxide and ethanol. Fungi are used on a major scale in industry to convert one complex organic molecule into another; many commercially important steroids are synthesized in this way.
TABLE 18.1 FUNGI
The four major fungal phyla, distinguished from one another primarily by their mode of sexual reproduction, are the zygomycetes, the ascomycetes, the basidiomycetes, and the chytridiomycetes. A fifth group, the imperfect fungi, is an artificial grouping of fungi in which sexual reproduction has not been observed; these organisms are assigned to an appropriate group once their mode of sexual reproduction is identified. Molecular data are contributing to our understanding of the fungal phylogeny and as additional molecular evidence is acquired, a new fungal phylogeny is likely to appear. However, it already seems clear that fungi are more closely related to animals than to plants.
Key Learning Outcome 18.4. The fungal phyla are distinguished primarily by their modes of sexual reproduction. However, molecular sequence data will undoubtedly result in changes to the fungal phylogeny in the future.