R-L categories correct, but text here does not match final assessment. Developed and updated version published at IUCN´s Red List update, July 18th 2019.
Polyporus rhizophilus is a peculiar small polypore with greyish cap and a black stipe base. It inhabits the rhizomes of various steppe grasses, e.g. feather grass (Stipa). Its trophic guild is unclear, one assumes parasitism or a kind of mycorrhiza, but it could also live purely saprotroph. It is everywhere a very rare species growing on steppe grasses with special habitat needs and thus in disappearing habitats. The species is endangered by habitat loss and habitat change. It is on several European Red Lists and at least classified as endangered. Its distribution area comprises the dry steppe zone in continental Eurosiberia, the Mediterranean region (Algeria), and coastal dune areas, mostly in agreement with the host grasses. The area extends from North Africa on Central Europe in the Ukraine, to the Baltic Sea (Mecklenburg-Western Pomerania) to southwestern Siberia (Kazakhstan) and probably even further to the east in little explored steppes of Central Asia. It is also found in North America. Based on GBIF, databases available (see below), and personal communication (Olga Morozova, Sergei Bolshakov) 125 subpopulations are known worldwide. The number of mature individuals has been estimated at 2500. The AOO was estimated as being 848 km2.
Concerning its habitats, like sand dunes, steppe grasslands and semidry grasslands, these habitats are highly endangered and declining. In Austria they are all in the red list of biotope types (Essl & Egger 2010). Polyporus rhizophilus is endangered by habitat loss, habitat change, abandonment of traditional forms of agriculture, bush encroachment, eutrophication through nearby intensive agriculture (entry of nutrients from the atmosphere and from adjacent agricultural areas).
Taking in account the IUCN criteria it is Vulnerable with criterium A3c, because population size reduction is suspected due to habitat loss and habitat management changes, and B2ab(iii), because of an AOO of 848 km2, and C2ai the number of mature individuals being only 2120 and the number of mature individuals in each subpopulation less than < 250.
The assessment is based on population size, habitat loss and habitat management changes.
Picipes rhizophilus (Pat.) J.L. Zhou & B.K. Cui, in Zhou, Zhu, Chen & Cui, PLoS ONE 11(8): e0159495, 16 (2016)
≡ Cerioporus rhizophilus (Pat.) Zmitr. & Kovalenko, International Journal of Medicinal Mushrooms (Redding) 18(1): 33 (2016)
= Polyporus cryptopus Ellis & Barthol., Erythea 4: 79 (1896)
≡ Polyporus rhizophilus Pat., J. Bot., Paris 8(12): 219 (1894)
= Scutiger cryptopus (Ellis & Barthol.) Murrill, Bull. Torrey bot. Club 30(8): 428 (1903)
In Europe it is everywhere a very rare species growing on steppe grasses with special habitat needs. It occurs in disappearing habitats. The species is endangered by habitat destruction and habitat change across Europe. It is on several European Red Lists of Central European countries and at least classified as endangered.
Polyporus rhizophilus grows in the dry steppe zone in the continental Eurosiberia (Russia, Ukraine, Kazakhstan), in the Mediterranean region (Algeria, Morocco), and in coastal dune areas, mostly in agreement with the host grasses. The type site is located in a plateau in Algeria. The area extends from North Africa on Central Europe in the Ukraine, to the Baltic Sea (Mecklenburg-Western Pomerania) to southwestern Siberia (Kazakhstan) and probably even further to the east in little explored steppes of Central Asia. It is also present in North America. There is one record from Brazil and one from China.
Based on GBIF, databases available (see below) and personal communication (Olga Morozova, Sergei Bolshakov) 125 subpopulations are known worldwide. The number of mature individuals has been estimated at 2500 following these lines: (a) likely number of current localities (estimated to be ca. 250) (b) translation of the estimated total number of localities to an estimate of the total number of mature individuals in 2 steps (i calculate the number of functional individuals (ie. sporomata separated by 10 m, template = 2, = 500): estimation of total number of localities x estimation of the average number of functional individuals/locality; ii convert the number of functional individuals into mature individuals following Dahlberg & Mueller 2010, template = 5, for terrestrial fungi each functional individual is suggested to account for 10 mature individuals; however, this grass sheats inhabiting species I never found more than two mature individuals at one site, so five is by far enough = 2500). The numbers of known localities are 125 and the number of yet unknown localities was estimated to be twice as high.
The AOO was estimated as being 848 km, based on the following assumption: 2 x 2 m = 4 km2 for each locality, because almost all of the basidiospores of a mature fruit body are deposited within this area.
For the AOO one has also to consider spore dispersal distance. Most spores of a mature individual are dispersed within 10s of metres, only a minor proportion is dispersed over longer distances (Norros et al. 2012) Due to competition with other spores and other established mycelia, colonization ability leading to a new generation via spore germination and establishment is only possible with a high number of spores deposited. This high number is only reached within the above mentioned 60-80 m, meaning that the AOO of a single ramet and its offspring is no more than 80 m. So calculating with the suggested 2 x 2 km2 is more than sufficient for AOO. For taxa that have a cryptic life form (such as fungi) occurrences may be estimated by tallying the area of 2 x 2 km2 (= 4 km2) grid cell in which observation records are located using equation 4.1. (IUCN Guidelines 2017): AOO = no. occupied cells × area of an individual cell. As it is still very difficult to have accurate distribution data, in case of macromycetes the no. of occupied cells is equated with no. of sites known.
Population Trend: Decreasing
This rare polypore inhabits the rhizomes of various steppe grasses. In Austria it grows exclusively on feather grass (Stipa), further hosts are Agropyron (common couch grass), Bothriochloa (bearded grass), Calamagrostis (horse grass), Chrysopogon (gold beard), Cynodon (dog tooth grass), Digitaria, Elymus, Elytrigia (hair muck), Festuca (fescue) and Poa. Its trophic guild is unclear, one assumes parasitism or a kind of mycorrhiza, but it could also live purely saprobiont. The fruiting bodies grow in conjunction with dead leaf sheaths of the grasses. However, loose hyphal nets surround the living grass roots.
It is endangered by habitat loss, habitat change, abandonment of traditional forms of cultivation (stop of mowing or grazing, conversion into agricultural fields, transformation into forests for biomass plant production), bush encroachment, eutrophication through nearby intensive agriculture (entry of nutrients from the atmosphere and from adjacent agricultural areas).
Habitat protection and management, such as controlled grazing and control of bush encroachment, reduction of nutrient input from adjacent agriculture are needed.
Research on distribution area, population size and population trends is needed.
It is not used and not traded.
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IUCN Standards and Petitions Subcommittee. 2017. Guidelines for using the IUCN Red List Categories and Criteria. Version 13. Prepared by the Standards and Petitions Subcommittee. http://nc.iucnredlist.org/redlist/content/attachment_files/RedListGuidelines.pdf
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