Sclerotium

A sclerotium (skləˈroʊʃəm; : sclerotia (skləˈroʊʃə), is a compact mass of hardened fungal mycelium containing food reserves. One role of sclerotia is to survive environmental extremes. In some higher fungi such as ergot, sclerotia become detached and remain dormant until favorable growth conditions return. Sclerotia initially were mistaken for individual organisms and described as separate species until Louis René Tulasne proved in 1853 that sclerotia are only a stage in the life cycle of some fungi. Further investigation showed that this stage appears in many fungi belonging to many diverse groups. Sclerotia are important in the understanding of the life cycle and reproduction of fungi, as a food source, as medicine (for example, ergotamine), and in agricultural blight management. Examples of fungi that form sclerotia are ergot (Claviceps purpurea), Polyporus tuberaster, Psilocybe mexicana, Sclerotium delphinii and many species in Sclerotiniaceae. Although not fungal, the plasmodium of slime molds can form sclerotia in adverse environmental conditions. Sclerotia are often composed of a thick, dense shell with thick and dark cells and a core of thin colorless cells. Sclerotia are rich in hyphae emergency supplies, especially oil. They contain a very small amount of water (5–10%) and can survive in a dry environment for several years without losing the ability to grow. In most cases, the sclerotium consists exclusively of fungal hyphae, whereas some may consist partly of fungal hyphae plexus and partly in between tissues of the substrate (ergot, Sclerotinia). In favorable conditions, sclerotia germinate to form fruiting bodies (basidiomycetes) or mycelium with conidia (in imperfect fungi). Sclerotia sizes can range from a fraction of a millimeter to a few tens of centimeters as, for example Laccocephalum mylittae, which has sclerotia with diameters up to 30 cm and weighing up to 20 kg. Sclerotia resemble cleistothecia in both their morphology and the genetic control of their development.