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PHYLUM GLOMEROMYCOTA

INTRODUCTION TO THE GLOMEROMYCOTA

Glomeromycota (glo-me-ro-mi-KO-ta] is made of a Latin root and a Greek root that mean ball (glomus); and fungus (mykes -μύκης), respectively. The reference may be to the arbuscular (shrub-like), ball-of-yarn masses of mycelia in the common genus, Glomus, for which the phylum was named.

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 A&B). 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 C), a rare soil fungus that grows in association with the liverwort, Riccia, lives as a lichen with endosymbiotic Nostoc.

A. Sporangia of Glomus.

B. Hyphae of Paraglomus inside a corn root.

C. Geosiphon, a soil fungus in symbiotic relationship with Nostoc on the surface of soil.

Images taken from:
A: http://res2.agr.ca/ecorc/ginco-can/photos/GSP4-1.jpg
B: http://invam.caf.wvu.edu/fungi/taxonomy/Paraglomaceae/occultum/occultum.htm
C: http://www.tu-darmstadt.de/fb/bio/bot/schuessler/geosiphon/geosiphon_home.html

SYNOPTIC DESCRIPTION OF THE GLOMEROMYCOTA

The following description comes from Schussler et al. (2001).

I. SYNONYMS: arbuscular mycorrhizal fungi

II. NUMBER: >150 species.

III. PHYLUM CHARACTERISTICS:

A. ASEXUAL REPRODUCTION:

Chlamydospores in some; complex with spores produced singly, loose clusters or sporangia (without peridia).

B. SEXUAL REPRODUCTION:

None known.

C. VEGETATIVE HYPHAE:

Coenocytic; with a few cross walls.

D. CELL WALLS: Chitin and chitosan.

E. ECOLOGY: Mostly hypogeal and symbiotic with plant roots.

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 emerges 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].

HIERARCHICAL CLASSIFICATION OF THE GLOMEROMYCOTA

This system is from Schussler et al. (2001).

CLASS GLOMEROMYCETES

ORDER GLOMERALES

Septa formed in older hyphae. Chlamydospores mainly terminal. Defined by ssu rRNA sequences.

Glomus

ORDER PARAGLOMERALES

Defined by ssu rRNA sequences.

Paraglomus..

ORDER DIVERSISPORALES

With or without hypogynous auxillary cells;forming comples spores within a sac on a base that grows from a sporogenous hypha. Defined by ssu rRNA sequences.

Acaulospora (and some species of Glomus).

ORDER ARCHAESPORALES

Forming endocytosymbioses; spores form singly or in loose clusters. Defined by ssu rRNA sequences.

Archaespora, Geosiphon.

This page is maintained by Jack R. Holt. Last revised 03/03/2008.