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Chapter 2

The diversity of fungi and

fungus-like organisms

This chapter is divided into the following major sections:

• overview of the fungi and fungus-like organisms


• the true fungi (Kingdom Mycota): Chytridiomycota,
  Glomeromycota, Zygomycota, Ascomycota,
  Basidiomycota, mitosporic fungi


• the cellulose-walled fungus-like organisms (Kingdom
  Straminipila)


• other fungus-like organisms: slime moulds, cellular
  slime moulds (acrasids and dictyostelids), and
  plasmodiophorids

In this chapter we focus on the major groups of fungi

and fungus-like organisms, covering the whole span

of fungal diversity in its broadest sense. We will use

selected examples to illustrate key features of the

fungal groups, and their biological significance. There

will be some surprises in store. For example, we will

see that some of the most devastating plant

pathogens are not fungi at all, but belong to an

entirely separate kingdom. We will see that some of

the organisms once considered to be among the

most “primitive” – the microsporidia, trichomonads,

and diplomonads (see Fig. 1.1) – are derived from fungi

by the loss of features such as mitochondria, which they

once possessed. We will also see how the development

of molecular methods for determining the relationships

between organisms has enhanced our understanding

of fungi in many respects, but there is still no consensus

on the best way to construct phylogenetic trees. In the

words of Patterson & Sogin (Tree of Life Web Project,

see Online Resources): “The consequence... has been

to demolish the model of the 1990s, but not to replace

it with something better.”

Overview of the fungi and fungus-like

organisms

Box 2.1 shows all the fungi and fungus-like organisms

that are currently considered to be fungi in the broad-

est sense. The vast majority are true fungi, sometimes

Box 2.1The several types of organism that constitute the

fungi in a broad sense.

Kingdom: Fungi (Mycota)

Probably derived from a choanoflagellate ancestor

Phylum Chytridiomycota

Phylum Zygomycota

Phylum Glomeromycota

Phylum Ascomycota

Phylum Basidiomycota

Kingdom: Straminipila

Probably derived from the protist group

containing golden-brown algae, diatoms, etc.

Phylum Oomycota

Phylum Hyphochytridiomycota

Phylum Labyrinthulomycota

Fungus-like organisms of uncertain affinity

Phylum Myxomycota(plasmodial slime

moulds)

Phylum Plasmodiophoromycota

(plasmodiophorids)

Phylum Dictyosteliomycota(dictyostelid slime

moulds)

Phylum Acrasiomycota(acrasid slime moulds)

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