Melanoleuca melaleuca

Appearance

*Cap: 3.5 – 8 cm, low convex, often with a low umbo, smooth, dark brown fading to greyish brown.
⤷ Gills: Whitish, crowded, emarginately attached to stipe.
⤷ Stipe: Up to 10 cm long and typically 1 cm thick, similarly coloured to the cap but lighter, with longitudinal fibres.
⤷ Spores: 6.5 - 8.5 x 5 - 6 µm, elliptical with amyloid warts , spore print white.
⤷ Odor: Faint.
⤷ Microscopic features: May have fusiform cheilocystidia or they may be missing .
⤷ Habitat: Grassy places in woods, roadsides, heathland etc.

This description is taken from several references, which generally agree except on microscopic features.

Due partly to the confused taxonomic definitions, this mushroom is very difficult to identify with certainty. Various authorities imply that around ''M. melaleuca'' there is a complex of closely related species without clear dividing lines, and that the current analysis requires more clarification. Much of the taxonomic work on ''Melanoleuca'' has been done in Europe and the status of North American specimens is less certain. However a 2012 paper by Vizzini et al. proposes updated definitions based on DNA analysis and suggests that some progress on these issues is being made.

Naming

Both the species name ''melaleuca'' and the genus name ''Melanoleuca'' come from the same Ancient Greek words for black and white . The species name was originated by the Swedish mycologist Persoon in his 1801 publication ''Synopsis Methodica Fungorum'', as ''Agaricus melaleucus''. This formed the basis for the genus name ''Melanoleuca'' which was invented by Narcisse Théophile Patouillard in 1897 as a variant of ''Melaleuca''.

The underside of the cap is whitish, and the top of the cap and the stem are often quite a dark brown, but "black and white" is not a very accurate description in practice.

The species names of common animals are often identical to their genus names , but this form of designation is forbidden for plants and fungi by the International Code of Nomenclature. ''Melanoleuca melaleuca'' narrowly circumvents this rule.

Patouillard had originally named the genus ''Melaleuca'' in 1887 and called the type species ''Melaleuca vulgaris'', presumably to avoid a tautonym. In 1897 Patouillard changed the name of the genus to ''Melanoleuca''. According to modern nomenclatural rules, the older genus name should normally take precedence, but an exception has been made by the International Botanical Congress and ''Melanoleuca'' has been declared a ''nomen conservandum'', that is, a name which is to be considered valid irrespective of the rules of precedence.

The American mycologist William Murrill devised the name ''Melanoleuca melaleuca'' in a 1911 article in the journal ''Mycologia''. If that is a valid name, again following modern rules, it should take precedence over ''Melanoleuca vulgaris'' as it refers to the original species name ''melaleucus''. But in any case, Species Fungorum gives ''M. vulgaris'' as a synonym of ''M. polioleuca'', rather than of ''M. melaleuca'' , and Bon implies that ''M. vulgaris'' is equivalent to only part of ''M. melaleuca''.

In certain treatments of the genus, including Funga Nordica and Flora Agaricina Neerlandica, ''M. melaleuca'' is defined as having no cheilocystidia, but molecular analysis by Vizzini et al. makes it clear that these cystidia may sometimes appear and sometimes be missing in the same species of ''Melanoleuca'', implying that this feature should not be used to characterize the mushroom. Other treatments specify ''M. melaleuca'' as having fusiform cheilocystidia, but recognize a separate closely related species, ''Melanoleuca graminicola'' as having no cheilocystidia. According to Index Fungorum the latter is a valid current name, but the former two references consider ''M. graminicola'' to be a synonym of ''M. melaleuca''.

According to its definition , Funga Nordica also lists ''Melanoleuca brachyspora'', ''Melanoleuca brevispora'', ''Melanoleuca robertiana'' and ''Melanoleuca stridula'' as synonyms of ''M. melaleuca''.

The older treatments use various characteristics to delimit the species, for instance Moser distinguishes ''M. melaleuca'' as not having a pruinose cap, with a long stem in relation to the cap diameter, having a dark brownish cap colour, with stem not coarsely striate, and having white stem flesh.

Another species which has been confused with ''M. melaleuca'' is ''Melanoleuca polioleuca''. In Species Fungorum , apart from the valid entry of ''M. melaleuca'', there is an invalid one designated "''Melanoleuca melaleuca sensu'' NCL" which is said to be equivalent to the current ''M. polioleuca''. According to Courtecuisse, ''M. polioleuca'' is distinguished by having a dense white "pruina" on the stem and by the flesh inside the stem being dark cinnamon rather than pale.