Geopyxis carbonaria is a species of fungus in the genus Geopyxis, family Pyronemataceae. First described to science in 1805, and given its current name in 1889, the species is commonly known as the charcoal loving elf-cup, dwarf acorn cup, stalked bonfire cup, or pixie cup. The small, goblet-shaped fruitbodies of the fungus are reddish-brown with a whitish fringe and measure up to 2 centimetres (3⁄4 in) across. They have a short, tapered stalk. The fungus is distributed throughout many temperate regions of the Northern Hemisphere. It is found in Europe, Turkey, and North America. Fruitbodies are commonly found on soil where brush has recently been burned, sometimes in great numbers. Although it is primarily a saprotrophic species, feeding on the decomposing organic matter remaining after a fire, it also forms biotrophic associations with the roots of Norway spruce.
Taxonomy The fungus was first described scientifically from Europe in 1805 by Johannes Baptista von Albertini and Lewis David de Schweinitz as Peziza carbonaria. Mordecai Cubitt Cooke illustrated the fruitbodies, spores, and asci in his 1879 work Mycographia, seu Icones fungorum. Figures of fungi from all parts of the world. In 1889, Pier Andrea Saccardo transferred the fungus to the genus Geopyxis, giving the species its current name. Pustularia carbonaria, published by Heinrich Rehm in 1884, is a synonym of G. carbonaria. Louis-Joseph Grélet proposed the variety Geopyxis carbonaria var. sessilis in 1937, referring to forms producing fruitbodies without a stalk, but the taxon is not considered to have independent taxonomic significance. In 1860 Miles Berkeley and Moses Ashley Curtis described the species Peziza lepida from collections made in Japan as part of the North Pacific Exploring and Surveying Expedition (1853–1856). This taxon was synonymized with G. carbonaria by Mien Rifai in 1968, a taxonomic opinion corroborated by Donald Pfister about a decade later.
Etymology The specific epithet carbonaria derives from the Latin word for "charcoal". Common names given to the fungus include "charcoal loving elf-cup", "dwarf acorn cup", "pixie cup", and the British Mycological Society approved "stalked bonfire cup".
Description The fruitbodies (ascocarps) of Geopyxis carbonaris are cup shaped, 5–20 millimetres (1⁄4–3⁄4 inch) wide, and have fringed whitish margins. The inner spore-bearing surface of the cup, the hymenium, is brick red and smooth, while the exterior surface is a dull yellow, and may be either smooth or have blister-like spots (pustules). The stipe, if present, is whitish, up to 15 mm (5⁄8 in) long and 2 mm wide, and expands abruptly into the cup. The brownish flesh of the fungus is thin and brittle. It does not have any distinctive taste, but has an unpleasant smell when crushed in water.
Microscopic characteristics In mass, the spores are whitish. The spores are elliptical, smooth, hyaline, devoid of oil droplets (eguttulate), and have dimensions of 13–18 by 7–9 μm. They are thin walled and germinate and grow rapidly in vitro in the absence of external stimuli. The asci are 190–225 by 9–10 μm. The paraphyses are slightly club-shaped, unbranched, and have irregular orange-brown granules, with tips up to 5 μm wide, and are not forked or lobed. The hypothecium, the layer of cells below the hymenium, is made of densely packed, small irregular cells.
Similar species
The closely related vulcan elf cup (Geopyxis vulcanalis) has a pale orange to yellowish fruitbody that is deeply cup shaped before flattening in maturity, and its crushed flesh often has an odor of sulfur. It may be distinguished microscopically by its paraphyses, which lack the orange-brown granules characteristic of G. carbonaria. It also has larger spores, measuring 14–22 by 8–11 μm. Unlike G. carbonaria, it grows on substrates other than burned wood, including mosses, and needle duff. Tarzetta cupularis, which grows habitats similar to G. carbonaria, is distinguished microscopically by its spores that contain two oil droplets. Tarzetta catinus is also similar. Other genera with similar species with which G. carbonaria may be confused include Aleuria, Anthracobia, Caloscypha, Melastiza, Pithya, and Sowerbyella.
Distribution and habitat G. carbonaria is widespread throughout North America from Alaska south, excluding the Gulf Coast region; it appears from March to June on the West Coast and April to September elsewhere. It is also found in Europe, and in 2010, was reported for the first time from Turkey. The fungus is widespread on burned soil or charcoal in the spring and throughout the growing season. It is one of the most common pioneer species found on burned ground. The charred litter on the forest floor increases the underlying soil pH as well as the availability of minerals. Fruitbodies are produced from 16 to 139 weeks after a forest fire in areas with coniferous trees. Most fruitbodies are produced in the first year after a burn. The fungus prefers fruiting in microhabitats with thin postfire duff near standing burned tree trunks. Geopyxis carbonaria fruitbodies are often found in the same post-fire stands as morels, although the former is usually more abundant. Because the pixie cup fruits earlier than morels, it may serve as an indicator of imminent morel fruiting. Other cup fungi often found fruiting in the same area as G. carbonaria include those from the genera Aleuria, Anthracobia, Peziza, and Tarzetta.
Ecology
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