Traditionally the family Hygrophoraceae, also known as waxy caps or waxcaps, was a taxon of white-spored agarics. Among them are some of the most brightly coloured fungi encountered, often in grasslands, forests and mossy areas across the northern hemisphere.
The common name "waxy cap" comes from the waxy feel and appearance of the gills or lamellae and often of the entire fruiting body. This characteristic may be subtle, and it is often difficult to identify some species as members of this group by relying on this characteristic alone. The lamellar attachment ranges from adnate to subdecurrent (fully decurrant in Camarophyllus), and the lamellae themselves are typically widely spaced.
The most distinct microscopic characteristic of this group are the very long basidia. The spores are unpigmented, inamyloid, smooth, and ellipsoid to elongate in shape. The pileipellis is usually a cutis, except in Camarophyllopsis, which has a hymenoderm pileipellis. Ecologically, most members of this family are ectomycorrhizal, except for Hygrocybe, which are mostly saprotrophs.
This family consists of several genera that are distinguished from each other by the arrangement of the lamellar trama, by the macroscopic appearance of the fruiting body, especially the coloration, and by their ecological niche.
Modern authors have been divided as to whether to treat all members of the Hygrophoraceae as one large genus, Hygrophorus, or to segregate them into various genera, including Hygrophorus, Hygrocybe, Camarophyllus (= Cuphophyllus), Camarophyllopsis (= Hygrotrama), Humidicutis, Bertrandia, and Neohygrophorus. L. R. Hesler and Alexander H. Smith (1963) took the former approach, while other authors such as Rolf Singer (1958), Marcel Bon (1984), David Boertmann (1996), and Anthony M. Young (2005) have recognized Hygrophorus plus one or more segregate genera.
Molecular phylogenetic analysis by J-M Moncalvo, et al (2002) revealed that several non-waxy cap genera, Chromosera and Chrysomphalina are also nested within the Hygrophoraceae, while Neohygrophorus was not closely related to the core group of Hygrophoraceae.
The Hygrophoraceae has been recognized by the majority of modern authors (eg, Singer, 1958; Bon, 1984; Largent, 1985; Boertmann, 1996; and Young, 2005), however, Eef Arnolds (1986) and Cornelis Bas (1990) have sunk the entire group into the Tricholomataceae. Some secondary sources (eg, Kirk, 2001) continue to use Arnold's and Bas' classification provisionally given the unsettled state of fungal nomenclature in the early 2000s. (Kuo, 2003) Young (2002, 2005) notes that though Moncalvo's analysis shows Hygrophoraceae to be polyphyletic, Tricholomataceae is even more so and will probably be split, so that adding the former to the latter will compound the problem. Young (2002) also notes that combining the two families would represent a continuation of the highly outdated concept that all white-spored genera belong in one taxon.