|The scarlet H. coccinea and Cuphophyllus virgineus, Wyre Forest, UK|
(Schaeff.) P.Kumm. (1871)
Hygrocybe is a genus of agarics (gilled fungi) in the family Hygrophoraceae. Called waxcaps in English (sometimes waxy caps in North America), basidiocarps (fruit bodies) are often brightly coloured and have waxy to slimy caps, white spores, and smooth, ringless stems. In Europe they are characteristic of old, unimproved grasslands (termed waxcap grasslands) which are a declining habitat, making many Hygrocybe species of conservation concern. Elsewhere they are more typically found in woodlands. Most are ground-dwelling and all are believed to be moss associates. Around 150 species are recognized worldwide. Fruit bodies of several Hygrocybe species are considered edible and are sometimes offered for sale in local markets.
Hygrocybe was first published in 1821 by Swedish mycologist Elias Magnus Fries as a subsection of Agaricus and in 1871 was raised to the rank of genus by Kummer. In several papers, Karsten and Murrill used the name Hydrocybe, but this is now taken as an orthographic variant of Hygrocybe. The generic name is derived from the Greek ῦγρὁς (= moist) + κυβη (= head).
Despite its comparatively early publication, the genus Hygrocybe was not widely accepted until the 1970s, most previous authors treating it as a synonym of Hygrophorus, a related genus of ectomycorrhizal agarics.
Hygrocybe itself has been split into subgenera, several of which – notably Cuphophyllus (= Camarophyllus sensu Singer, non Fries) and Gliophorus Herink – have subsequently been raised to generic rank. Some species, such as the mauve splitting waxcap (Humidicutis lewelliniae), have been described in the small genus Humidicutis.
Recent molecular research, based on cladistic analysis of DNA sequences, suggests that Hygrocybe as currently understood is paraphyletic and does not form a single clade within the Hygrophoraceae. As a result, the genus Cuphophyllus (comprising Hygrocybe pratensis and its allies) was removed from Hygrocybe sensu stricto, together with the genus Gliophorus (comprising Hygrocybe psittacina and its allies) and several other genera.
Fruit bodies of Hygrocybe species are all agaricoid, most (but not all) having smooth to slightly scaly caps that are convex to conical and waxy to slimy when damp. Many (but not all) are brightly coloured in shades of red, orange, or yellow – less commonly pink or green. Where present, the gills beneath the cap are often equally coloured and usually distant, thick, and waxy. One atypical South American species, Hygrocybe aphylla, lacks gills. The stems of Hygrocybe species lack a ring. The spore print is white. Fruit bodies of some species, notably Hygrocybe conica, blacken with age or when bruised. Microscopically, Hygrocybe species lack true cystidia and have comparatively large, smooth, inamyloid basidiospores.
Habitat, nutrition, and distribution
Most species of Hygrocybe are soil-dwelling, though a few (such as Hygrocybe mexicana and H. rosea) are only known from mossy tree trunks or logs. In Europe, species are typical of unimproved (nutrient-poor), short-sward grasslands, often termed "waxcap grasslands", but elsewhere they are more commonly found in woodland.
Their metabolism has long been debated, but recent research suggests that they are not saprotrophic  but rather symbiotically associated the roots of higher plants or mosses. Hyphae of H. conica have been detected in plant roots  and other waxcap species have been detected as systemic endophytes of Plantago lanceolata.
Species are distributed worldwide, from the tropics to the sub-polar regions. Around 150 have been described to date. Waxcaps receive most attention in northern Europe, where they are found in nutrient-poor pastures. However, outside Europe, waxcaps are more commonly associated with woodland habitats, for example the sclerophyll forests site at Bush Lane Cove, Sydney.
In Europe, waxcap grasslands and their associated fungi are of conservation concern, since unimproved grasslands (formerly commonplace) have declined dramatically as a result of changes in agricultural practice. As a result, by 1993, 89% of European Hygrocybe species appeared on one or more national red lists of threatened fungi.
In several countries, action has been taken to conserve waxcap grasslands and some of the rarer Hygrocybe species. Guidance
In the United Kingdom, some grasslands have gained a measure of legal protection as Sites of Special Scientific Interest because of their waxcap interest, notably Llanishen Reservoir in Cardiff, where the original SSSI notification by the Countryside Council for Wales in 2006  was upheld following judicial review.
Because Hygrocybe species cannot be maintained in culture, none is cultivated commercially. Fruit bodies of a few species are considered edible in eastern Europe, south-east Asia, and Central America and are collected and consumed locally.
No comprehensive monograph of the genus has yet been published. In Europe, however, species of Hygrocybe have been illustrated and described in a standard English-language guide by Boertmann (2010) and also (together with Hygrophorus) in an Italian guide by Candusso (1997). European species have also been covered, more briefly, in descriptive French keys by Bon (1990). Dutch species were illustrated and described by Arnolds (1990). No equivalent modern guides have been published for North America, the most recent being by Hesler & Smith (1963). There is, however, a guide to Californian species by Largent (1985). In Australia, Hygrocybe species have been illustrated and described by Young (2005) and in New Zealand by Horak (1990).
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