Pisolithus arrhizus - Dyeball

Taxonomy

Phylum: Basidiomycota

Class: Agaricomycetes

Order: Boletales

Family: Sclerodermataceae

When young, the earthball fungus Pisolithus arrhizus (syn. Pisolithus tinctorius) is shaped rather like a rugby ball. Its traditional use as a source of dye led to it acquiring the common name Dyeball.

Because it forms mycorrhizae with almost any kind of root, this ectomycorrhizal fungus is frequently used by foresters (and in recent years by gardeners, too) as the basis of a soil inoculant to promote tree and plant growth - particularly in remediation of areas of degraded or polluted land or formerly clear-felled forest areas.

Progressively from the top, the whole of the fruitbody turns into a soft mass of brown spore-bearing powder. At maturity cracks appear in the upper surface and the spores blow away on the breeze or get washed away to new locations in wet weather.

Identification Guide

	Internal structure Initially the inside of a Pisolithus arrhizus fruitbody comprises many separate compartments, looking like rice grains, within which the spores develop.
	Spores The whole of the fruitbody becomes a brown powdery mass.
Odour/taste	Not significant.
Habitat	Most often found with trees in soft sandy soil, particularly in coastal pine forests.
Season	Summer and autumn.
Occurrence	Rare in Britain and Ireland but very common in southern parts of mainland Europe.
Similar species	Much more likely to be mistaken for horse dung than for another fungus.