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Calocybe gambosa (St George’s mushroom)

St George's mushroom is one of the few good edible fungi to be found in spring, usually appearing in late April close to St George's Day (23 April), hence the popular name.

Dissected St George's Mushroom

Dissected Calocybe gambosa (Photo: Malcolm Storey, 1999, www.bioimages.org.uk)

Species information

Common name: 

St George’s mushroom

Conservation status: 

Widespread and fairly common in the UK, and not considered of conservation concern. Status regarded as IUCN category ‘least concern’ in Europe.

Habitat: 

Found in grassy places, roadside verges and woodland edge.

Known hazards: 

None.

Taxonomy

Kingdom: 
Fungi
Phylum: 
Basidiomycota
Subphylum: 
Agaricomycotina
Order: 
Agaricales
Family: 
Lyophyllaceae
Genus: Calocybe

About this species

St George’s mushroom is a distinctive species, one of the few larger fungi to appear regularly in spring. It is quite common in various grassy habitats and is a good edible fungus, recognised by the convex, whitish cap, the white, closely-spaced gills, and strong floury odour.

The fungus we refer to today as Calocybe gambosa has long been known and was first described by Linnaeus who, in his Species Plantarum published in 1753, named it Agaricus georgii, after St George. This name is not used today as the name Agaricus gambosus was applied by the great Swedish mycologist Elias Magnus Fries whose seminal work on fungi Systema Mycologicum, was published in 3 volumes from 1821-32. Names used by Fries take priority. The name Calocybe derives from the Greek kalos, meaning pretty, and cubos, head.

Genus: 
Calocybe

Discover more

Geography and distribution

Calocybe gambosa is widespread and found in temperate regions throughout much of Europe including parts of Russia, and Asia, including Korea and Japan.

Description

Calocybe gambosa fruitbody (Photo: Malcolm Storey)

Calocybe gambosa has fleshy, whitish or pale tan fruitbodies and a mealy smell, and is quite distinctive. It fruits from spring to early summer (April to June) and is usually found growing in groups, sometimes forming fairy rings.

St George’s mushroom is unlikely to be confused with other species. However, some inedible or slightly poisonous Entoloma species appear in spring and can be similar, though these are usually browner or greyish and have pink gills when mature. They also lack the distinctive mealy odour of C. gambosa.

The cap of the fruitbody is whitish to cream or pale tan, convex, fleshy, smooth and 5 to 12 cm across. The margin of the cap is somewhat incurved (rolled under). The stipe (stalk) is central, cylindric, smooth and the same colour as the cap. The stipe is stout, 3 to 7 cm high and 1.5 to 3 cm thick. The gills are white or cream, sometimes with yellow-brown tints when older, closely spaced, with sinuate attachment (the gills shorten and curve back down the stipe a little before attaching). The spore deposit is white. The flesh has a strong, floury odour.

Calocybe gambosa was once thought to belong in the large genus Tricholoma, which similarly includes fleshy agarics with white spore deposit and sinuate gill attachment. However, true Tricholoma species are ectomycorrhizal (they grow in a mutually beneficial association with trees), whereas Calocybe species are saprotrophs (feeding on decaying organic matter).

Several other species were thought to belong to the genus Calocybe, some found in grassy places, others in woodlands. They mostly have smaller fruitbodies than C. gambosa, and some of the commoner ones have attractive pink or purple colours, but they are not necessarily edible. However, recent work has shown that these species are better placed in other genera, including Tricholomella and Rugosomyces.

Only one other British species is now placed in Calocybe, the very rare but attractive C. favrei, which occurs in woodlands on calcareous soil. It differs from C. gambosa in having blue-grey fruitbodies with bright yellow gills.

Threats and conservation

No specific threats are known and the species is not currently considered as of conservation concern. However, it is commercially collected in some areas and the effects of this on populations of the fungus are little known.

Uses

This is an excellent edible fungus, sought-after as a culinary delicacy throughout its range. It has also been reported to have important medicinal properties including antibacterial activity. A dichloromethane compound extracted from this species has been reported to be active against some bacteria, including Escherichia coli. However, antibacterial properties have not been confirmed in other studies. The species has also been reported to reduce blood sugar levels. A substance called phenoxazone, which can be used in the pest control of nematode worms, has been isolated from the St George’s mushroom.

Collecting

This is an excellent edible species if collected in good condition. Like most fleshy fungi, fruitbodies are prone to attack by fly larvae, and are best collected when young. Furthermore, fruitbodies from roadside verges should be avoided due to possible pollution from vehicle exhausts.

St George's mushroom at Kew

Calocybe gambosa is frequent in the Gardens wherever suitable habitat occurs (for example grassy places and woodland edge).

Preserved specimens of Calocybe gambosa from throughout its range are maintained in the Kew Mycology Herbarium and, although not accessible to the general public, are available for study by research workers worldwide.

References and credits

Barros, L., Cruz, T., Baptista, P., Letícia M. Estevinho, L.M. & Isabel C.F.R. Ferreira, I.C.F.R. (2008). Wild and Commercial Mushrooms as Source of Nutrients and Nutraceuticals. Food and Chemical Toxicology 46: 2742–2747.

Brachvogel, R. (1986). Blutzuckersenkung Durch Calocybe gambosa (Fr.) Donk. Zeitschrift für Mykologie 52(2):445.

Clémençon, H. (1981). Phenoxazones in cultures of species of Calocybe (Agaricales). Proceedings of the International Botanical Congress 1981, 13:160.

Clémençon, H. (1987). Phenoxazone in Mycelkulturen von Calocybe-arten (Agaricales, Basidiomycetes). Beiträge zur Kenntniss der Pilze Mitteleuropas 3: 107 – 115.

Encyclopedia of Life. Calocybe gambosa.  Available online.

Fungus Records Database of Britain and Ireland. Available online.

Keller, C., Maillard, M., Keller, J. & Hostettmann, K. (2002). Screening of European Fungi for Antibacterial, Antifungal, Larvicidal, Molluscicidal, Antioxidant and Free-radical Scavenging Activities and Subsequent Isolation of Bioactive Compounds. Pharmaceutical Biology 40(7): 518-525.

Kew Mycology Herbarium. Available online.

Schlunegger, U.P., Kuchen, A. & Clémençon, H. (1979). Mycelium products in higher fungi. i. phenoxazine derivatives in Calocybe gambosa. Helv. Chim. Acta 59(4):1383-8.

Kew Science Editor: Brian Spooner

While every effort has been taken to ensure that the information contained in these pages is reliable and complete, the notes on hazards, edibility and suchlike included here are recorded information and do not constitute recommendations. No responsibility will be taken for readers’ own actions.

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