Stropharia aeruginosa (Curtis) Quél. - Verdigris Roundhead

Phylum: Basidiomycota - Class: Agaricomycetes - Order: Agaricales - Family: Strophariaceae

Stropharia caerulea - Blue Roundhead

Stropharia aeruginosa is one of very few blue-green fungi. (In most instances the caps are much nearer to green than to blue, but when young and fresh they are very beautiful and quite startling.) The caps, initially bell-shaped, flatten and turn paler from the centre. White scales adorn young caps of this remarkable fungus.

The fine specimens pictured on the left were photographed by Janet Hill, with whose kind permission they are shown here.

Distribution

This attractive mushroom is a rare find and very localised in Britain and Ireland, occurring mainly in alkaline areas of humus-rich Beech woodland and parkland. These striking mushrooms are found throughout mainland Europe and they are also recorded in parts of North America.

Taxonomic history

Although this blue mushroom has been known to science for more than two centuries, its separation from Stropharia caerulea had not been clearly defined until, in 1979, the German mycologist Hanns Kreisel (b. 1931) published a paper in Sydowia (an international Mycological journal produced in Austria), which established Stropharia caerulea as a distinct species.

The basionym of this species was created when the Verdigris Roundhead was described in 1782 by British naturalist William Curtis (1746 - 1799), who gave it the binomial scientific name Agaricus aeruginosus. It was French mycologist Lucien Quélet who, in 1872, established the currently-accepted scientific name of this species as Stropharia aeruginosa.

Synonyms of Stropharia aeruginosa include Agaricus aeruginosus Curtis,  and Pratella aeruginosa (Curtis) Gray.

Etymology

Stropharia, the genus name, comes from the Greek word strophos meaning a belt, and it is a reference to the stem rings of fungi in this generic grouping. The specific epithet aeruginosa means deep blue-green.

Identification Guide

Cap of Stropharia aeruginosa

Cap

Young caps are bell-shaped, blue-green and slimy, peppered with small white veil fragments. Older specimens, like the one illustrated here, are paler and often lose the white scales from the rim of the cap, which expands but does not completely flatten out. In sunlight the slime dries up on older caps, which gradually turn pale tan from the centre outwards.

The cap diameter at maturity ranges between 2.5 and 8cm.

Gills of Stropharia aeruginosa

Gills

At first pale grey, the moderately crowded adnate gills become purple-brown as the spores mature.

The gill margins (see left) remain white, which helps distinguish the Verdigris Roundhead Stropharia aeruginosa from the more commonly encountered Blue Roundhead Stropharia caerulea, whose gill edges gradually turn brown along with the gill faces.

Stem

Whitish above the ring, which is transient and soon discoloured brown by falling spores; darker blue-green below the ring zone and peppered with coarse white scales. 5 to 12 mm in diameter and 2 to 6cm tall.

 

Spores

Ellipsoidal, smooth, 7.5-9 x 4.5-5μm, with a germ pore.

Spore print

Purple-black.

Odour/taste

Not distinctive. (Caution: probably poisonous.)

Habitat & Ecological role

Saprobic, usually in small groups among grass and occasionally leaf litter in woodland and in pastures.

Season

July to October in Britain and Ireland; up to three months later in southern Europe.

Similar species

Stropharia caerulea is paler blue-green and its cap scales are usually evident only on young fruitbodies; it has brown gills without white edges. In Britain this species is much more common than Stropharia aeruginosa .

Clitocybe odora is also blue-green but does not have a slimy cap with scales; it has a strong odour of aniseed.

Culinary Notes

Together with other fungi in the genus Stropharia, the Verdigris Roundhead is inedible. In the USA it is listed by several authorities as one of the mushrooms that can contain significant amounts of the toxic hallucinogens psilobin and psilocybin. Although, with the possible exception of Sulphur Tuft Hypholoma fasciculare, no member of the family Stropharicae is known to be dangerously poisonous, some of the Stropharia species can certainly cause very unpleasant gastro-intestinal symptoms. We therefore treat Stropharia aeruginosa as just for looking, and definitely not for cooking.

Reference Sources

Fascinated by Fungi, Pat O'Reilly 2016.

BMS List of English Names for Fungi

Dictionary of the Fungi; Paul M. Kirk, Paul F. Cannon, David W. Minter and J. A. Stalpers; CABI, 2008

Taxonomic history and synonym information on these pages is drawn from many sources but in particular from the British Mycological Society's GB Checklist of Fungi and (for basidiomycetes) on Kew's Checklist of the British & Irish Basidiomycota.

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