A Species of Fungus
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Basis for Listing
This red-spored mushroom species is endemic to Minnesota. Psathyrella rhodospora was first collected in 1971 in Rice County near Nerstrand Woods State Park. It has more recently been reported at a single location in Hennepin County in 1998, 1999, and 2001 (McLaughlin 1998), and at a single location in Ramsey County in 2003 and 2004. Its population size appears to be very small and its distribution extremely limited. Psathyrella rhodospora was listed as an endangered species in Minnesota in 1996.
Psathyrella rhodospora has an irregularly convex cap up to 85 mm (3.3 in.) broad. It is light yellowish brown or yellowish white to pale light brown and has a white stipe. The grayish reddish brown spores on its gills distinguish it from other Psathyrellas, and occasionally spore deposits can be seen on its cap. Smith (1972) mentions that it resembles P. variata but can be distinguished by its broad gills, 5-6 mm (0.20-0.24 in.) wide. This species also resembles P. sublateritia, which has a medium reddish brown spore print, but P. sublateritia is concentrically zoned with bands of brownish pink and light reddish brown when fresh. Microscopically, P. rhodospora can be separated statistically from P. sublateritia, which has longer basidiospores.
Psathyrella rhodospora was originally found on the stump of a Tilia americana (basswood) tree. The more recent finds have been on and beside a large, undecayed Populus deltoides ssp. monilifera (cottowood) stump located on a bank above the Mississippi River (McLaughlin 1998) and under a large P. deltoides located on the St. Paul campus of the University of Minnesota.
Biology / Life History
Not much is known about the biology of P. rhodospora. It is presumably saprobic on wood, although its resource specificity is not known. It is a saprotroph and is usually found in small groups or scattered. The species is found on or beside the stumps of deciduous trees. It may fruit in successive years, based on recent scientific observations. A search for this mushroom in the same location one year later relocated the species, but it was a smaller collection (McLaughlin 1999). At present it seems best to preserve the associated tree stump, as it is not known how important this is for fruiting. Psathyrella rhodospora is likely dispersed in the form of mycelia (thread-like structures that make up the body of a fungus) and spores. Low nutrient availability probably triggers the growth of the mushroom in this species. The earliest documentation of this species is the 13th of June and the latest is the 12th of September. Because P. rhodospora has only been reported three times, it is difficult to specify its life history. Additional studies should reveal more information about its biology.
Conservation / Management
Psathyrella rhodospora seems to require recently dead deciduous trees with the bark intact. Unlike several other rare fungi species in Minnesota, it has not been observed with Quercus spp. (oak). Its conservation may require forests where recently dead trees are allowed to decay undisturbed.
Conservation Efforts in Minnesota
Surveys for P. rhodospora have been conducted in four counties with searches based in Nerstrand Woods State Park, Afton State Park, Wolsfeld Woods Scientific and Natural Area, Belwyn Educational Center, and the Minnesota Valley National Wildlife Refuge. Research has been conducted on the separation of P. rhodospora from P. sublateritia (Padamsee 2001).