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Rhizopogon alexsmithii (Trappe) Vizzini & Zotti

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Scientific name
Rhizopogon alexsmithii
Author
(Trappe) Vizzini & Zotti
Common names
 
IUCN Specialist Group
Cup-fungi, Truffles and Allies
Kingdom
Fungi
Phylum
Basidiomycota
Class
Agaricomycetes
Order
Boletales
Family
Rhizopogonaceae
Assessment status
Published
Assessment date
2015-04-23
IUCN Red List Category
EN
IUCN Red List Criteria
B2ab(ii,iv,v); C1+2a(i)
Assessors
Castellano, M. & Bérubé, J.
Reviewers
Dahlberg, A.

Assessment Notes

The content on this page is fetched from The IUCN Red List of Threatened Species: https://www.iucnredlist.org/species/75121617/75121859

Justification

Easily recognized hypogeous mycorrhizal, sequestrate species endemic to the Pacific Northwest of North America. Characterized by the knobby to lobed sporocarp and the pink to flesh-coloured and white marbled gleba. Known only from mid to high elevational Tsuga forests in the Cascade Mountains. Eleven total known sites, five are historic and not re-documented for more than 30 years. Historic sites include the single localities in both Canada and Washington. Six extant sites all located within Oregon in the Cascade mountains. Random Grid survey of 750 plots for two years across this region, including plots in this habitat type, did not reveal any new collections or sites for this species. The total number of mature individuals is estimated to be fewer than 500 based on the following calculation; 11 known sites x 2 potential mycelia per site x 2 ramets per mycelia x 10 for potential yet unknown sites (summing up to 440 potential mature individuals, following Dahlberg and Mueller 2011). The area of occupancy is 450 km2 and the population is severely fragmented. It therefore qualifies for listing as Endangered.



Taxonomic notes

Originally proposed as Alpova alexsmithii Trappe (1975).  Transferred to Rhizopogon by Vizzini and Zotti (2010) based on molecular evidence.

Geographic range

Endemic to the Pacific Northwest of North America. Known from southwestern British Columbia, Canada and the Cascade Mountains of Washington and Oregon in USA.

Population and Trends

Ten known sites in Pacific Northwest USA and one known site in southwestern British Columbia, Canada.

Six of the 10 known sites from Oregon and Washington are from more than 30 years old.  Only one known site from that timeframe has been redocumented; Still Creek campground on the Mount Hood National Forest has 6 additional collections up through 2004.  The Canadian and Washington sites have been revisited numerous times without re-documentation of species presence.

Random Grid survey of 750 plots for two years across this region, including plots in this habitat type, did not reveal any new collections or sites for this species.

Extremely small population size, habitat declining due to forest fire and logging.

Population Size: there are eleven known sites, x 2 potential mycelia per site, x 2 ramets per mycelia = 44 mature individuals x 10 (for potential other mature individuals) = 440 potential mature individuals (see Dahlberg and Mueller 2011).

Population Trend: decreasing


Habitat and Ecology

This is a mycorrhizal fungus species so it is dependent on living host trees for population viability. This mutually beneficial, symbiotic association between fungus and plant host roots conveys numerous critical advantages for plant host survival. Mycorrhizal fungi are essentially the uptake organs for many nutrients i.e., nitrogen, phosphorus, numerous micronutrients, i.e., boron, selenium, copper, and plays a major role in uptake of water.  Both the fungus and the plant host does not exist in nature without each other.

Hypogeous, mycorrhizal sequestrate species forming mycorrhiza  with the roots of mature to old-growth Abies procera, A. lasiocarpa, Tsuga mertensiana or Tsuga heterophylla (Trappe 1975). Characterized by the knobby to lobed sporocarp and the pink to flesh-coloured and white marbled gleba. Most known sites are located at 3,000-6,000 ft. (900-1,800 m) elevation.  Home range of primary spore vector (small mammals) is less than 2 ha. 


Threats

This is a mycorrhizal fungus species dependent on living host trees for viability. Threats to the high elevation late serial to old growth habitat include, logging, and human activities such as campground development and road building. Forest fire is of concern due to remote locations of some known sites. Summer forest fires are common near these known site locations due to dry summer thunderstorms. Soil compaction in known sites that are campgrounds. In addition climate change have potential severe impacts on habitat availability.

Conservation Actions

The ongoing action plan as part of the Survey and Manage plan of the Northwest Forest Plan to protect habitat for the Northern Spotted Owl is to protect known sites and buffer known sites from ground and host disturbances. It is important to revisit known sites to confirm persistence and determine extent of populations, particularly for known sites more than 30 years old. Mitigate impacts during vegetation management (clear-cutting or thinning of surrounding forests) in or near known sites.

Use and Trade

This is a truffle fungus and is presumably edible.

Source and Citation

Castellano, M. & Bérubé, J. 2015. Rhizopogon alexsmithii. The IUCN Red List of Threatened Species 2015: e.T75121617A75121859. https://dx.doi.org/10.2305/IUCN.UK.2015-4.RLTS.T75121617A75121859.en .Downloaded on 31 January 2021

Country occurrence