R. crustosa are also recognized. One author even suggests that R. virescens "is strictly a European species", citing Buyck and collaborators (2006), who say "the virescens-crustosa group is much more complex than suspected and embraces at least a dozen taxa in the eastern US". As in Europe, Russula virescens has a widespread distribution in Asia, having been recorded from India, Malaysia, Korea, the Philippines, Nepal, China, Thailand, and Vietnam. It is also found in North Africa and Central America. Chemistry Russula virescens has a limited capacity to bioaccumulate the micronutrients iron, copper, and zinc from the soil. The concentration of these trace metals is slightly higher in the caps than the stipes. A meal of fresh mushroom caps would supply 16% of the recommended daily allowance (RDA) of copper for an adult male or female (ages 19–50); 16% or 7.3% of the RDA of iron for an adult male or female, respectively; and 16–22% of the adult RDA of zinc. The mushroom is a poor bioaccumulator of the toxic heavy metals arsenic, cadmium, lead, mercury, and nickel. Biologically active mushroom polysaccharides have been a frequent research topic in recent decades due to their possible stimulatory effect on innate and cell-mediated immune responses, antitumor activities, and other activities. Immunostimulatory activity, antioxidant activity, cholesterol-lowering, and blood sugar-lowering effects have been detected in extracts of R. virescens fruit bodies, which are attributed to polysaccharides. A water-insoluble beta-glucan, RVS3-II, has been isolated from the fruit bodies. Sulfated derivatives of this compound have antitumor activities against sarcoma tumor cell lines. RVP, a water-soluble polysaccharide present in the mushroom, is made largely of galactomannan subunits and has antioxidant activity. Ribonucleases (or RNases) are enzymes that catalyze the hydrolysis of ribonucleic acid (RNA), and collectively they play a critical role in many biological processes. A RNase from R. virescens was shown to be biochemically unique amongst seven edible mushroom species in several ways: it has a co-specificity towards cleaving RNA at poly A and poly C, compared to the monospecific RNases of the others; it can be adsorbed on chromatography columns containing DEAE–cellulose as the adsorbent; it has a pH optimum of 4.5, lower than all other species; and, it has a "distinctly different" N-terminal amino acid sequence. The mushroom contains a unique laccase enzyme that can break down several dyes used in the laboratory and in the textile industry, such as bromothymol blue, eriochrome black T,