Mushroom Hunting Underwater: Updates on Psathyrella aquatica

Photo by R. Coffan

Written by Darlene Southworth

Southern Oregon University, Ashland, Oregon, USA

In 2005, Robert Coffan observed mushrooms growing underwater in the Rogue River in southern Oregon. In 2007, he took Jonathan Frank and me to see them. At that moment, I understood that there were mushrooms fruiting under about 0.5 m of water in the river. Based on morphology and molecular evidence and a lot of personal determination, we described this population as a new species, Psathyrella aquatica, in 2010 (Mycologia 102/1:93-107). Since then we have continued to survey the population.

UPDATE #1: We have observed P. aquatica fruiting in a 1-km reach of the Rogue River every summer from 2007 through 2018. Sometimes they are on both sides of the river and upstream. They definitely live there. In 2018, we extended our observations of fruiting from mid-June through late September, an unusually long fruiting period for any terrestrial mushroom.

UPDATE #2: We have surveyed for additional populations up- and downstream, in tributaries of the Rogue, and in other streams, but have found no new locations. Surely they are somewhere, but where?

UPDATE #3: Occasionally we get a phone call or email of a possible sighting, e.g., in Fish Lake and in Clear Creek in the Kalmiopsis Wilderness, but none of these turned out to be P. aquatica. We had a report of an underwater mushroom in Upper Payette Lake, Idaho, by Joe Blume in October 2016. Based on the specimens he sent us, this was definitely Psathyrella, but not P. aquatica, possibly P. prona. We did not find it in 2017, but he saw it again in 2018. Conditions at this stream entrance are controlled to some extent by a dam.

UPDATE #4: We wondered whether this species also grew on land and, after 10 years, found it on the grassy bank near the main population. It also fruits as an emergent on gravel or waterlogged wood near the underwater specimens.

For further information, watch the movie Aquatica: The Underwater Mushroom

Look underwater for Psathyrella aquatica next summer (June through September). If you see it, send a sign: