INTRODUCTION TO THE GLOMEROMYCOTA

The arbuscular mycorrhizal (AM) fungi are among the most important fungi on earth. They are soil fungi that enter into symbiotic relationships with the roots of vascular plants (Figures 1 and 2). Smith and Read (1997) report that the symbiosis is almost necessary for the plants, particularly in obtaining their required phosphorus, an element that adheres stubbornly to soil particles. Almost all terrestrial plants have AM symbioses. Schussler et al. (2001) report that the action of AM fungi influences plant biodiversity (and thereby all terrestrial biodiversity), helps to control pests and fungal pathogens, and affects plant fitness in polluted areas. Geosiphon (Figure 3), a rare soil fungus that grows in association with the liverwort, Riccia, lives as a lichen (text with tooltip) Organism formed by symbiotic association between fungi and green algae or cyanobaccteria. with endosymbiotic Nostoc.

FIGURE 1. Sporangia of Glomus. Image from http://res2.agr.ca/ecorc/ginco-can/photos/GSP4-1.jpg	FIGURE 2. Hyphae of Paraglomus inside a corn root. Image from http://invam.caf.wvu.edu/fungi/taxonomy/Paraglomaceae/occultum/occultum.htm	FIGURE 3. Geosiphon, a soil fungus in symbiotic relationship with Nostoc on the surface of soil. Image from http://www.tu-darmstadt.de/fb/bio/bot/schuessler/geosiphon/geosiphon_home.html

FIGURE 4. A cladogram showing the relationships between Glomeromycota (taxon in the shaded box) and the other fungal taxa. The topology is supported by James et al. (2006) and Porter et al. (2011).

SYSTEMATICS OF THE GLOMEROMYCOTA

Schussler et al. (2001) conducted a ssu r-RNA comparison with 72 taxa and “about 100” sequences. The AM fungi emerged as a monophyletic clade. However, the chytrids and the zygomycetes emerged as 2 and 4 separate clades, respectively. The monophyly of the Glomeromycota was confirmed by Helgason et al. (2003) and by Lutzoni et al. (2004) [see also Lang, The Fungal Mitochondrial Genome Project].