Leucocoprinus birnbaumii

The species was first published as Agaricus luteus by the English mycologist James Bolton who described and illustrated it from a hothouse near Halifax in 1785.[4] Unfortunately, the name A. luteus had already been published for a different fungus, making Bolton's A. luteus illegitimate. Nonetheless, many popular North American books continued to use the name Lepiota lutea until the 1980s.[5][6] In 1839 Czech mycologist August Corda described the same species from Prague where it was found growing in a greenhouse by a garden inspector named Birnbaum, hence the epithet birnbaumii.[7]

Fruit bodies of Leucocoprinus birnbaumii are agaricoid (mushroom-shaped) and occur singly or in small clumps. All parts are bright, pale sulphur-yellow, but fade with age. When young, the cap is usually taller than broad, later becoming convex and around 20–60 mm (1–2.5 in) across. The cap surface is smooth but dotted with fine, easily detached scales, and often develops shallow, radial grooves near the margin. The gills are free (not attached to the stem) and are covered by a partial veil when young, which ruptures to leave a fragile, evanescent ring on the stem. Microscopically, the species is distinguished by its thick-walled, ellipsoid spores that are dextrinoid, have a germ pore, and measure around 8–12 by 5–9 μm.[11]

A single fruit body of L. birnbaumii

Like all Leucocoprinus species, L. birnbaumii is a saprotroph, living on very decayed plant matter (humus or compost). The fungus is common throughout the tropics and subtropics, extending into warmer parts of the temperate zones. Rarely, it appears in cooler areas, fruit bodies having been recorded as far north as England,[13] but these seem to be temporary introductions. In these areas (such as North America, Europe, and Australia) it is more usually found in hothouses and plant pots than in the wild.[9][14]

The yellow color of the mushrooms is from alkaloids known as birnbaumins;[15] whether these compounds are toxic is unknown.