Psathyrella aquatica is a species of fungus from Oregon, first described in the journal Mycologia in 2010.^[1] It represents the first ever report of a gilled basidiomycete fruiting underwater.

Quick Facts Psathyrella aquatica, Scientific classification ...

Psathyrella aquatica
Scientific classification
Domain:	Eukaryota
Kingdom:	Fungi
Division:	Basidiomycota
Class:	Agaricomycetes
Order:	Agaricales
Family:	Psathyrellaceae
Genus:	Psathyrella
Species:	P. aquatica
Binomial name
Psathyrella aquatica J.L.Frank, Coffan, & Southworth (2010)

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Quick Facts Psathyrella aquaticaMycological characteristics ...

Psathyrella aquatica Mycological characteristics
	Gills on hymenium
	Cap is convex
	Hymenium is free
	Ecology is saprotrophic
	Edibility is unknown

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It was found by Southern Oregon University professor Robert Coffan in the Rogue River in the U.S. state of Oregon.^[1] Coffan and his colleagues, Darlene Southworth and Jonathan Frank, found the mushroom in 2005. The biology department at Southern Oregon University confirmed that the mushroom was a unique discovery.^[1] Once their research was published, it was named one of the most significant species discovered in 2010.^[2] They have so far been discovered in a 1 kilometer stretch of the river, and have an observed fruiting season of mid-June to late September^[3] Many scientists were skeptical about describing this mushroom as a new species because of the hundreds of similar looking species in the family Psathyrellaceae.^[2][4]

Less than 1% of aquatic fungi are assumed to be discovered yet, and many are assumed to be microscopic, with only a small fraction thought to produce fruiting bodies.^[5]

The fruiting body consists of a small convex cap and a long stipe.^[1] Its cap is brown, convex, and has gills underneath.^[1] The young mushroom develops a veil, which is lost as the mushroom grows to maturity.^[1] The mushroom's stipe appears to be quite strong, and is anchored up to 1.6 feet (0.5 m) deep in sediment, in order to stand up to the fast-moving river currents where it is primarily found.^[1] The stipe is covered in thin hair like structures.^[1] Spores released by the gills stay in gas bubbles underneath the gills before floating to the top of the water to spread.^[1] Underwater gills and ballistospores suggest that its underwater adaption is a relatively recent one.^[1]

When synthetically grown, P. aquatica are known to only fruit (produce stipe and cap) underwater. A study done in 2014 by one of the original authors of the discovery paper showed that this species only produces sporocarps when completely submerged under cold water.^[6]

The mushrooms are found growing out of water-logged wood, silt, and gravel, a fine volcanic substrate, and was observed growing from youth to maturity completely underwater over 11 weeks.^[1] The mushroom grows submerged under fast, cold, running water of the river.^[1] The water is spring fed, aerated, and contains lots of woody debris and is shallow in depth.^[1] They are found growing about a half a meter underneath the water.^[3] The mushroom is also found growing on land in either grassy banks, or on gravel or water-logged wood next to the river.^[3]

Though not enough is known about the species to consider it edible, scientist assume that it is a food source for small insects in the river.^[2] Though the river has low levels of nitrogen, nitrogen-fixing cyanobacteria near mushroom discovery sites suggests they might provide a source of nitrogen.^[7]

The taxonomy of the species is in reference to the habitat the mushroom is found in. Aquatica is a Latin word meaning water or watery (relating to water, aquatic).^[8]