PortaBella Spore Print (Agaricus bisporus)
The caps of the Pearl Oyster Mushroom may be laterally attached (with no stipe). If there is a stipe, it is normally eccentric and the gills are decurrent along it. The term pleurotoid is used for any mushroom with this general shape.
The spores are smooth and elongated (described as "cylindrical"). Where hyphae meet, they are joined by clamp connections. Pleurotus is not considered to be a bracket fungus, and most of the species are monomitic (with a soft consistency). However, remarkably, Pleurotus dryinus can sometimes be dimitic, meaning that it has additional skeletal hyphae, which give it a tougher consistency like bracket fungi.
Pleurotus fungi are found in both tropical and temperate climates throughout the world.Most species of Pleurotus are white-rot fungi on hardwood trees, although some also decay conifer wood. Pleurotus eryngii is unusual in being a weak parasite of herbaceous plants, and P. tuber-regium produces underground sclerotia. In addition to being saprotrophic, all species of Pleurotus are also nematophagous, catching nematodes by paralyzing them with a toxin.
Oyster mushrooms are popular for cooking, torn up instead of sliced, especially in stir fry or sauté, because they are consistently thin, and so will cook more evenly than uncut mushrooms of other types. They are often used in vegetarian cuisine.
Phylogeny The classification of species within the genus Pleurotus is difficult due to high phenotypic variability across wide geographic ranges, geographic overlap of species, and on going evolution and speciation. Early taxonomic efforts placed the oyster mushrooms within a very broad Agaricus as Agaricus ostreatus (Jacq. 1774). Paul Kummer defined the genus Pleurotus in 1871; since then, the genus has been narrowed with species moving to other genera such as Favolaschia, Hohenbuehelia, Lentinus, Marasmiellus, Omphalotus, Panellus, Pleurocybella, and Resupinatus. See Singer (1986) for an example of Pleurotus taxonomy based on morphological characteristics.
More recently, molecular phylogenetics has been utilized to determine genetic and evolutionary relationships between groups within the genus, delineating discrete clades. Pleurotus, along with the closely related genus Hohenbuehelia, has been shown to be monophyletic. Tests of cross-breeding viability between groups have been used to further define which groups are deserving of species rank, as opposed to subspecies, variety, or synonymy. If two groups of morphologically distinct Pleurotus fungi are able to cross-breed and produce fertile offspring, they meet one definition of species. These reproductively discrete groups, referred to as intersterility groups, have begun to be defined in Pleurotus. Many binomial names used in literature are now being grouped together as species complexes using this technique, and may change.