Tricholoma pardinum

Tricholoma pardinum, commonly known as spotted tricholoma, tiger tricholoma, tigertop, leopard knight, or dirty trich, is a gilled mushroom widely distributed across North America and Europe, as well as parts of Asia. It is generally found in beech woodland in summer and autumn. Two subspecies have been described from southern Europe. First officially described by Christiaan Hendrik Persoon in 1801, Tricholoma pardinum has had a confusing taxonomic history that extends over two centuries. In 1762, German naturalist Jacob Christian Schäffer described the species Agaricus tigrinus with an illustration corresponding to what is thought to be T. pardinum, and consequently, the name Tricholoma tigrinum has been used erroneously in some European field guides. The fruit body of Tricholoma pardinum is an imposing mushroom with a pale grey cap up to 15 cm (6 in) in diameter that is covered with dark brownish to greyish scales. The gills are whitish, and are not attached to the stout white to pale grey-brown stalk. The spore print is white. One of the more toxic members of the genus Tricholoma, the species has been implicated in a number of episodes of mushroom poisoning, probably because it is a large, attractive mushroom with a pleasant smell and taste, and it bears a superficial resemblance to several edible species, like Tricholoma terreum. Ingesting T. pardinum—even in small quantities—results in a severe, persistent gastroenteritis caused by an unknown mycotoxin. Christiaan Hendrik Persoon described this species as Agaricus myomyces var. pardinus in 1801, although he queried whether it was a distinct species. However, the German naturalist Jacob Christian Schäffer had in 1762 published Fungorum qui in Bavaria et Palatinatu circa Ratisbonam nascuntur Icones, in which he described a mushroom he called Agaricus tigrinus. The illustration accompanying the name fits what we now know as Tricholoma pardinum, although the description is less clear. To confuse matters further, Elias Magnus Fries used the name Agaricus tigrinus in his 1821 work Systema Mycologicum, in accordance with Bulliard's 1782 description, which now corresponds with Lentinus tigrinus. In his 1838 work Epicrisis systematis mycologici: seu synopsis hymenomycetum, Fries assigned a different fungus again to the binomial name and linked it to Schäffer's 1762 description. French mycologist Lucien Quélet reclassified it as a species in 1873, giving it its current binomial name. Italian mycologist Alfredo Riva has noted that Swiss mycologist Louis Secretan provided a description forty years before Quélet, in his 1833 work Mycographie Suisse, and queried why it was ignored. He has proposed the fungus be written as Tricholoma pardinum (Secr.) Quél. However, Secretan's works are generally not recognised for nomenclatural purposes because he did not use binomial nomenclature consistently. There has been confusion over which scientific name to use for over two hundred years. Tricholoma tigrinum has been used in some European field guides, but has been applied in error to this species. The uncertainty was such that Czech mycologists Josef Herink and František Kotlaba suggested in 1967 that both designations were incorrect, and proposed the new name T. pardalotum. Tricholoma pardinum lies within the subgenus Pardinicutis of Tricholoma, a grouping of similar species characterised by greyish, brownish, or pallid caps that are woolly or covered in small scales, spores with a length between 8 and 11 micrometres, and abundant clamp connections in the hyphae. Molecular analyses suggest that T. pardinum is closely related to T. huronense, T. mutabile, and T. venenatum. Tricholoma pardinum var. filamentosum is an uncommon variety, described in 1983 by Carlo Luciano Alessio, which produces mushrooms with more fibrillose caps and stalks than the typical variety. It is found in southern Europe, where it associates with chestnut and spruce trees. Another variety has been described as T. pardinum var. unguentatum, characterised by daintier mushrooms that have a greasy coating on their caps. The specific epithet pardinum is derived from the Latin pardus 'leopard', referring to its mottled or spotted cap. The generic name derives from the Greek trichos/τριχος 'hair' and loma/λωμα 'hem', 'fringe', or 'border'. Common names include striped tricholoma, spotted tricholoma, tiger tricholoma, poison trich, leopard knight, and tigertop. Dirty trich was a name coined by author Gary H. Lincoff in response to a publisher's request for a more accessible name than its binomial one for North American guidebooks. The fruit body is a medium-sized mushroom, with a cap 6–10 cm (2.5–4 in) in diameter, though larger specimens occasionally reach 15 cm (6 in). The cap is initially hemispherical before flattening with maturity, and has a broad, shallow umbo. The cap margin is initially curled inwards but uncurls as it matures. The cap surface is silvery-grey and covered with concentrically patterned darker scales of a grey, brown or blackish colour that grow paler toward the cap margin, Secretan noting its resemblance to the cap of Sarcodon imbricatus. The gills are free (unattached to the stalk), white and thick, may have a yellow or greenish tint, and may drip water, as may the top of the stalk when broken. With age, the gill edges can become jagged and rough. The gill spacing is rather variable, ranging from distant to crowded; typically, between 100–120 gills extend fully from the stalk to the edge of the cap, with a variable number of lamellulae (shorter gills not extending fully from stalk to cap margin). The stout stalk may be white, pale grey or pale brown, and is thicker at the base. The texture of the stalk surface ranges from fibrillose (appearing to be made of coarse fibers arranged longitudinally) to more or less smooth, and the stalk base will stain a dirty brown to yellow colour when bruised. It is 3.0–8.0 cm (1.2–3.1 in) high and 1.5–2.0 cm (0.6–0.8 in) wide, with the base 2.5–4.0 cm (1.0–1.6 in) in diameter, and bruises a dirty yellowish colour. There is no ring or volva. The flesh is whitish and has a pleasant mealy smell and taste. Variety filamentosum has a mealy odour and taste reminiscent of cucumber. The spore print is white, and the oval to oblong spores are 7.5–9.5 μm long by 5.0–7.0 μm wide. Spores are smooth, hyaline (translucent), nonamyloid, and have a prominent hilum. The basidia (spore-bearing cells) are cylindrical to club shaped, four spored, and measure 39–50 by 8.0–9.6 μm. The cystidia present on the gill edge (cheilocystidia) are thin walled, hyaline, have a short stalk and a spherical apical portion, and measure 29–41 by 12–21 μm; cystidia are absent from the gill face. The cap cuticle ranges in cellular form from a cutis (in which the hyphae are bent over, running parallel to the cap surface) to a trichoderm (with hyphae emerging roughly parallel, like hairs, perpendicular to the cap surface); the hyphae comprising the cuticle are cylindrical, and measure 2.0–9.0 μm wide with a club-shaped tip up to 11 μm wide.