white chalk mushroom

Leucocoprinus cretaceus is a small dapperling mushroom with white flesh and a distinctively warty cap. Cap: 2–8 cm. Bulbous when immature becoming convex or flat as it grows and ages. It is stark white and covered in warts. Stem: 3–8 cm in height. 5-10mm thick. Tapers upwards from a swollen base which may exhibit similar warty scales. Fragile stem ring. Gills: White, free and crowded. Spore print: White to creamy white. Spores: Subamygdaliform or Ellipsoid. Smooth with a small pore. Dextrinoid. 6–12 x 4–7 μm. Smell: Indistinct. Flora Agaricina Neerlandica provides more detail: Cap: 3.8–9 cm wide, starting hemispherical to convex or conico-convex expanding and flattening with age to become plano-concave with or without a slight umbo. The surface is white and covered with woolly warts and scales (floccose squamulose) with a brownish yellow tinge at the centre of the cap. Gills: White to very pale cream, free and remote from the stem, crowded and very thin. Stem: 2.8–11 cm long and 2–13 mm thick with a bulbous clavate or fusiform base that is 7-19mm thick. The interior is solid but becomes stuffed with age and the exterior surface is white with a slight brownish yellow colour developing with age, more so in the top half. The surface is covered in a minute flocculose or felty coating above the ring with thicker warts below and towards the base. …

Leucocoprinus cretaceus is documented growing in plant pots and greenhouses and so may have a worldwide distribution in captivity with introduction into the wild being possible where temperatures are suitable for these tropical species. In a 1907 study the American mycologist Andrew Price Morgan documented Lepiota cretacea growing in 'rich soil in gardens' and in hot beds throughout North America. It is widespread in tropical areas, and has a scattered distribution in South America. Five species of Leucocoprinus collected recently in Northern Argentina and Paraguay were identified. Four of them (L. birnbaumii, L. cepistipes, L. cretaceous, and L. straminellus) were reported for the first time in Paraguay and later, three (Leucocoprinus birnbaumi, L. cepistipes, and L. straminellus) were reported in northeastern Argentina.

The specific epithet cretaceus means chalky and comes from the Latin creta for chalk.