Melanoleuca polioleuca (Fr.) Kühner & Maire - Common Cavalier

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

Melanoleuca polioleuca, Common Cavalier, Wiltshire, England

With a dark cap covering pallid gills, this is a tricky species to identify from macroscopic features alone; it occurs in deciduous broadleaf woodland and with conifers, notably pines, andit is a saprobic fungus (feeding on rotting wood and other organic vegetation).

It is very difficult to separate this species from some of the other brown-capped cavaliers such as Melanoleuca melaleuca, with more broadly ellipsoidal spores and no gill-edge cystidia.

Melanoleuca polioleuca, Common Cavalier, France

Distribution

Widespread and fairly common in Britain and Ireland, Melanoleuca polioleuca occurs throughout mainland Europe and is found also in North America.

Taxonomic history

This mushroom was described in 1821 by the great Sweddish mycologist Elias Magnus Fries, who gave it the name Agaricus polioleucus. (In the early days of fungal taxonomy, most of the gilled mushrooms were included initially in a huge genus Agaricus; later many new genera were erected into which the majority of species were transferred, so that nowadays the genus Agaricus is rather more manageable!) The Common Cavalier was transferred to the genus Melanoleuca in 1934 by German mycologist Robert Kühner (1903 - 1996) and French mycologist René Charles Joseph Ernest Maire (1878 - 1949).

Melanoleuca polioleuca, Common Cavalier, Hampshire, England

Synonyms of Melanoleuca polioleuca include Agaricus polioleucus Fr., Tricholoma melaleucum var. polioleucum (Fr.) Gillet, Melaleuca vulgaris Pat., Tricholoma polioleucum (Fr.) Sacc., Melanoleuca vulgaris (Pat.) Pat., and Melanoleuca polioleuca f. polioleuca (Fr.) Kühner & Maire.

Etymology

The genus name Melanoleuca comes from the Ancient Greek words melas meaning black, and leucos meaning white. No cavalier mushroom is truly black and white, but many have caps whose upper surfaces are various shades of brown, with whitish gills beneath.

The specific epithet come from poli- meaning grey or hoary, and leucos meaning black - so I suppose hoary greyish-black would be a literal translation and perhaps also a passable description.

Identification guide

Umbonate cap of Melanoleuca polioleuca

Cap

The appearance of caps is very variable from specimen to specimen and varies even more through the development life of the fruitbody. The cap is initially convex with a downturned margin, eventually flatenning and sometimes developing a central depression, usually with a small umbo; smooth; slightly greasy; dark grey-brown when moist, turning paler in dry weather; 4 to 8cm across when fully expanded.

Gills of the Common Cavalier mushroom

Gills

Sinuate; white, turning creamy-grey with age.

Stem

The stem is generally much longer than the cap diameter - often by as much as a factor of two. 4 to 10cm long and 0.5 to 1cm diameter; base slightly bulbous; white, covered in grey-brown fibrils that are densest towards base; no stem ring.

Spores of Melanoleuca polioleuca

Spores

Ellipsoidal, densely warty, 6.5-9 x 4-5μm; amyloid.

Show larger image

Spore print

Very pale cream.

Odour/taste

Odour faintly mealy; taste mild but not distinctive.

Habitat & Ecological role

On soil among leaf litter in all kinds of woods and forests and near trees in lawns and parks..

Season

July to November in Britain and Ireland.

Similar species

Melanoleuca melaleuca is macroscopically indistinguishable with certainty from the Common Cavalier, but it can be separated by microscopic examination of the spores, cystidia etc. Its spores are more broadly ellipsoidal (they have a lower ratio of major to minor diameter, which in mycologists refer to as having a lower Q factor) and it lacks gill-edge cystidia, which are present in Melanoleuca polioleuca.

More than thirty species in the Melanoleuca genus are recorded from Britain and Ireland, and most have brownish caps and white gills; separating them is a task for specialists. Many of them are very rare finds, whereas the Common Cavalier is by far the most widespread and abundant member of the group.

Culinary Notes

The Common Cavalier is reported as being edible but nothing special; however, as these kinds of mushrooms are notoriously difficult to identify and I recommend that they should be considered suspect and not collected for food..

Reference Sources

Fascinated by Fungi, Pat O'Reilly 2016.

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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