It may be mistaken for the edible St Georges' mushroom (Calocybe gambosa), or miller (Clitopilus prunulus) and has been responsible for many cases of mushroom poisoning in Europe. E. sinuatum causes primarily gastrointestinal problems that, though not generally life-threatening, have been described as highly unpleasant. It is generally not considered to be lethal, although one source has reported deaths from the consumption of this mushroom.
Entoloma sinuatum has been the most widely accepted scientific name since 1955, and was promoted as such by Michael Noordeloos in his recent work on the genus. Initially Noordeloos had erected the new name Entoloma eulividum for the common form of the species (as E. lividum was invalid) after separating the older description of E. sinuatum as it described a form lacking yellow colour on the gills, so for a time in the 1980s there were two accepted species - the widespread E. eulividum with yellow-tinged gills and now-restricted and rare E. sinuatum. However he later felt these were merely colour variations and so this is the name universally recognised. A proposal was later made to conserve Entoloma lividum in 1999, citing its previous widespread use and Quélet's detailed description. However it was rejected in 2001 because Bulliard's original name was invalid.
To complicate matters further, Quélet had proposed a broader genus Rhodophyllus for all pink-gilled fungi with adnate or sinuate gills and angular spores in 1886, countering Kummer's erection of Entoloma to genus level. These two classifications coexisted for many decades, with mycologists and guidebooks following either author, and the alternate scientific name Rhodophyllus sinuatus was commonly seen. However, later authorities have tended to favour Entoloma.
Thus, the current most widely accepted name is Entoloma sinuatum, the specific epithet sinuatum being derived from the Latin for wavy, referring to the shape of the cap, while the generic name is derived from the Ancient Greek words entos/ἐντός 'inner' and lóma/λῶμα 'fringe' or 'hem' from the inrolled margin. The specific epithet lividum was derived from the Latin word lividus meaning 'lead-coloured'. The various common names include livid entoloma, livid agaric, livid pinkgill, leaden entoloma, and lead poisoner. In the Dijon region of France it was known as le grand empoisonneur de la Côte d'Or ("the great poisoner of Côte d'Or"). Quélet himself, who was poisoned by the fungus, called it the millers purge, akin to another common name of false miller.
The spore print is reddish brown, with angular spores 8–11 x 7–9.5 μm, roughly six-sided and globular in shape. The stout white stipe is generally 6–10 cm (2½–4 in) high and lacks a ring. It may be bulbous at the base. The taste is mild, although it may be unpleasant. The mushroom's strong and unusual odour can be hard to describe; it may smell of flour, though is often unpleasant and rancid.
Confusion with the highly-regarded miller or sweetbread mushroom (Clitopilus prunulus) is a common cause of poisoning in France; the latter fungus has a greyish-white downy cap and whitish decurrent gills which turn pink with maturity. Entoloma sinuatum can also be confused with St Georges' mushroom (Calocybe gambosa), though the gills of the latter are crowded and cream in colour, and the clouded agaric (Clitocybe nebularis), which has whitish decurrent gills and an unusual odour. The rare and edible all white dovelike tricholoma (Tricholoma columbetta) has a satiny cap and stem and a faint, not mealy, odour. It may be confused with Clitocybe multiceps in the Pacific Northwest of North America, though the latter has white spores. A casual observer may mistake it for a field mushroom (Agaricus campestris).
Entoloma sinuatum has been found in fairy rings. Fruiting bodies are found in deciduous woodlands in late summer and autumn under oak, beech, and less commonly birch, often on clay soils, though they may also occur in parks. Most members of the genus are saprotrophic, though this species has been recorded as forming an ectomycorrhizal relationship with the willow (Salix).
Hospital treatment of poisoning by this mushroom is usually supportive; antispasmodic medicines may lessen colicky abdominal cramps and activated charcoal may be administered early on to bind residual toxin. Intravenous fluids may be required if dehydration has been extensive, especially with children and the elderly. Metoclopramide may be used in cases of recurrent vomiting once gastric contents are emptied.