Russula virescens

Russula virescens is a basidiomycete mushroom of the genus Russula, and is commonly known as the green-cracking russula, the quilted green russula, or the green brittlegill. It can be recognized by its distinctive pale green cap that measures up to 15 cm (6 in) in diameter, the surface of which is covered with darker green angular patches. It has crowded white gills, and a firm, white stipe that is up to 8 cm (3 in) tall and 4 cm (1.6 in) thick. Considered to be one of the best edible mushrooms of the genus Russula, it is especially popular in Spain and China. With a taste that is described variously as mild, nutty, fruity, or sweet, it is cooked by grilling, frying, sautéeing, or eaten raw. Mushrooms are rich in carbohydrates and proteins, with a low fat content. The species was described as new to science in 1774 by Jacob Christian Schaeffer. Its distribution encompasses Asia, North Africa, Europe, and Central America. Its presence in North America has not been clarified, due to confusion with the similar species Russula parvovirescens and R. crustosa. R. virescens fruits singly or scattered on the ground in both deciduous and mixed forests, forming mycorrhizal associations with broadleaf trees such as oak, European beech, and aspen. In Asia, it associates with several species of tropical lowland rainforest trees of the family Dipterocarpaceae. R. virescens has a ribonuclease enzyme with a biochemistry unique among edible mushrooms. It also has biologically active polysaccharides, and a laccase enzyme that can break down several dyes used in the laboratory and in the textile industry. Russula virescens was first described by German polymath Jacob Christian Schaeffer in 1774 as Agaricus virescens. The species was subsequently transferred to the genus Russula by Elias Fries in 1836. According to the nomenclatural authority MycoBank, Russula furcata var. aeruginosa (published by Christian Hendrik Persoon in 1796) and Agaricus caseosus (published by Karl Friedrich Wilhelm Wallroth in 1883) are synonyms of Russula virescens. The variety albidocitrina, defined by Claude Casimir Gillet in 1876, is no longer considered to have independent taxonomic significance. According to Rolf Singer's 1986 classification of Russula, R. virescens is the type species of subsection Virescentinae in section Rigidae, a grouping of mushrooms characterized by a cap surface that breaks into patches of bran-like (furfuraceous) particles. In a molecular phylogenetic analysis of European Russula, R. virescens formed a clade with R. mustelina; these two species were sister to a clade containing R. amoenicolor and R. violeipes. The specific epithet virescens is Latin for 'becoming green'. The characteristic pattern of the cap surface has earned the species common names such as the green-cracking russula, the quilted green russula, and the green brittlegill. In the mid-Atlantic United States, it is also known locally as the moldy russula. Described by mushroom enthusiast Antonio Carluccio as 'not exactly nice to look at', the cap is at first dome or barrel-shaped, becoming convex and flattened with age with a diameter of up to 15 cm (6 in). The cap center is often depressed. The cuticle of the cap is green, most profoundly in the center, with patches of the same color dispersed radially around the center in an areolate pattern. The color of the cuticle is often of variable shade, ranging from gray to verdigris to grass-green. The extent of the patching of the cuticle is also variable, giving specimens with limited patches a resemblance to other green-capped species of Russula, such as R. aeruginea. The green patches of the cap lie on a white to pale green background. The cap, while frequently round, may also exhibit irregular lobes and cracks. The cap cuticle is thin, and can be readily peeled off the surface to a distance of about halfway towards the cap center.The gills are white to cream colored, and fairly crowded together; they are mostly free from attachment to the stipe. Gills are interconnected at their bases by veins. The stipe is cylindrical, white, and of variable height, up to 8 cm (3 in) tall and 4 cm (1.6 in) wide; it is roughly the same thickness at both the top and the base. The top portion of the stipe may be farinose—covered with a white, mealy powder. It may turn slightly brown with age, or when it is injured or bruised from handling. Like other mushrooms in the Russulales, the flesh is brittle, owing to the sphaerocyst cytoarchitecture—cylindrical cells that contrast with the typical fibrous, filamentous hyphae present in other orders of the basidiomycota. The spores of R. virescens are elliptical or ellipsoid with warts, translucent (hyaline), and produce a white, pale or pale yellow spore print; the spore dimensions are 6–9 by 5–7 µm. A partial reticulum (net-like pattern of ridges) interconnects the warts. The spore-bearing cells, the basidia, are club-shaped and have dimensions of 24–33 by 6–7.5 µm; they are colorless, and each hold from two to four spores. The pleurocystidia (cystidia on the gill face) are 40–85 by 6–8 µm and end abruptly in a sharp point. Russula parvovirescens, found in the eastern United States, can be distinguished from R. virescens by its smaller stature, with caps measuring 4–8 cm (1.6–3.1 in) wide and stipe up to 6 cm (2.4 in) long by 2 cm (0.8 in) thick. Compared to R. virescens, it tends to be more bluish-green, the patches on its cap are larger, and it has a lined cap margin. Microscopically, the terminal cells in the cap cuticle of R. parvovirescens are more swollen than those of R. virescens, which has tapered and elongated terminal cells. Another green-capped Russula is R. aeruginea, but this species may be distinguished from R. virescens by its smaller size and smooth cap. Other green russulas with a smooth cap include R. heterophylla and R. cyanoxantha var. peltereaui. Russula crustosa, like R. virescens, also has an areolate cap, but the cap becomes sticky (viscid) when moist, and its color is more variable, as it may be reddish, yellowish, or brown. Also, the spore print of R. crustosa is a darker yellow than R. virescens. R. redolens has a cap that is 'drab-green to blue-green', but unlike R. virescens, is smooth. R. redolens has an unpleasant taste and smells of parsley. Russula virescens is an edible mushroom considered to be one of the best of the genus Russula, and is popular in Europe, particularly in Spain. In an 1875 work on the uses of fungi, English mycologist Mordecai Cubitt Cooke remarked about the mushroom that 'the peasants about Milan are in the habit of putting over wood embers to toast, and eating afterwards with a little salt.' The mushroom is often sold as a dried product in Asia, and in China, it can be found in roadside markets. Its smell is not distinctive, but its taste has been described as mild, nutty, fruity, or even sweet. Old specimens may smell of herrings. Drying the mushrooms enhances the nutty flavor. Mushrooms can be sautéed (the green color disappears with cooking), and young specimens that are prepared this way have a potato taste that pairs well with shallots. They are also fried or grilled, or used raw in salads. Young specimens are pale and can be hard to identify, but the characteristic pattern of older fruit bodies makes them hard to confuse with other species. When collecting R. virescens for consumption, caution is of vital importance to avoid confusion with the dangerously poisonous Amanita phalloides (known as the death cap), a mushroom that can be most easily identified by its volva and ring.