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  • Under Assessment
  • LCPreliminary Assessed
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Suillus weaverae (A.H. Sm. & Shaffer) Kretzer & T.D. Bruns

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Scientific name
Suillus weaverae
(A.H. Sm. & Shaffer) Kretzer & T.D. Bruns
Common names
IUCN Specialist Group
Mushroom, Bracket and Puffball
Assessment status
Preliminary Assessed
Preliminary Category
Proposed by
Patrick Leacock
Patrick Leacock
Comments etc.
Else Vellinga, Craig Hilton-Taylor, Anders Dahlberg

Assessment Notes

Least Concern (LC). The previously poorly known Suillus weaverae now appears to be the eastern North American “Suillus granulatus”, separate from the European taxon, based on soon to be published molecular work (Vellinga pers. comm.).

Taxonomic notes

  Fuscoboletinus weaverae A.H. Sm. & Shaffer, Michigan Bot. 4: 27 (1965).
  The distinctive features of S. weaverae are the glabrous and viscid cap, the yellow tubes when mature, the glandular dotted stem, and the brownish drab spore print color. The veil, the covering formed around the button-shaped young fruitbodies, is fibrillose (covered with silk-like fibers) to cottony. Veil color is white to pale cream. The veil sheathes the lower stem and tubes in young fruitbodies, remaining as a sheath on the lower stem or disappearing, but not forming a ring. It may leave patches on the cap margin. Spore print is light yellowish brown to light reddish brown when fresh, grayish to purplish brown when dry. Because of the spore print color, the species was originally placed in the genus Fuscoboletinus. This genus has now been merged with Suillus based on recent molecular studies (Kretzer et al. 1996).
  Unpublished discussion of DNA sequencing raise doubts on whether this is a distinct species separate from Suillus brevipes or S. granulatus. It is hard to recognize it, because a spore print is needed to clearly identify it. It is possible that this could be a spore color mutant of a closely related species but the odds are that it is genetically distinct, because of the spore color, and it might be a variety or subspecies of one of these related species. We hope that further molecular work can clarify the situation.

Why suggested for a Global Red List Assessment?

This species is not under consideration after it was discovered that current molecular work indicates that Suillus weaverae may represent the “Suillus granulatus” taxon for eastern North America.
  Suillus weaverae was listed as an endangered species in Minnesota in 1996., and thought to be endemic to Minnesota. This species, named in honor of its collector, has been collected twice in the same locality in Crow Wing County, where the documented population is small. The species has not been found on repeated visits to this site and nearby areas. It is not yet reported from anywhere else in the world.

Geographic range

Suillus weaverae is only known from the type locality in northern Minnesota, where the documented population is small. It has not been seen on a few return visits to the area. It is not yet reported from anywhere else in the world.

Population and Trends

  This species has been collected twice from one site in Minnesota, Crow Wing County, between Pelican and Markee Lakes, September 1964 and October 1969. No other occurrences are known. It was not found on a few return visits to that area.
  The original site represents one known population. The estimated population size is 1000 mature individuals factoring in the potential distribution in surrounding states: 1 known population × 5 functional individuals (genets) per subpopulation × 10 mature individuals (ramets) per genet × factor of 20 for potential sites.  This site uncertainty could be greatly reduced if intense surveys could be done in surrounding states.

Population Trend: Uncertain

Habitat and Ecology

The only known population of S. weaverae was found in humus in sandy soil of mixed deciduous-coniferous forest containing Quercus spp. (oak), Populus spp. (poplar), Betula spp. (birch), Pinus banksiana (jack pine), P. resinosa (red pine), and P. strobus (white pine). Suillus weaverae is a presumed ectomycorrhizal fungus that is a beneficial root symbiont. It is most likely associated with P. resinosa and P. banksiana.

ForestTemperate Forest


Only one Suillus weaverae population is currently known. The habitat is vulnerable to disturbance from human activity including habitat alteration or loss. Ectomycorrhizal fungi in general are sensitive to nitrogen deposition and other forms of pollution that affect the soil. Mycorrhizal fungi on sandy soils are especially susceptible to air and water pollution.

Conservation Actions

There are no past or current conservation actions for this species. The original type locality of Suillus weaverae on private land is not secure and an adjacent lot was cleared in 1998 of most trees and shrubs. Nearby areas of Crow Wing State Forest and Crow Wing State Park may be favorable for this species.
If further populations of the species can be located then protective conservation actions can be considered.

Site/area protectionSite/area managementAwareness & communications

Research needed

  In 1994, the Minnesota DNR funded a study to characterize the diversity and abundance of ectomycorrhizal fungi in old-growth and young northern hardwood-conifer forests. This species was not found during that 3 year study. Then in 1998, it was not found during two focused searches in several locations in Crow Wing State Park, Crow Wing State Forest and the original habitat of S. weaverae in September and October (however 1998 was a dry year and few boletes were seen during those visits).
  Surveys are needed to search for other potential populations and to monitor the known location of this species. The best time to search for S. weaverae is during its fruiting season. Based on related species, this would likely extend from July through early October in Minnesota.
  One of the problems with looking for this species is that the habitat has changed since it was first collected. Peg Weaver told McLaughlin that the forest was going through succession following fire when she first collected it, and the forest has matured since then. The MN DNR has sent staff recently to look for it in the nearby forest, but did not find it.
  Further molecular work is needed. The identity of this taxon has some uncertainty based on the two known collections. The MGW-1992 collection (12 October 1969) is similar in ITS-region to a Suillus brevipes collection (Kretzer et al. 1996). The ITS of the type collection (MGW-1086, 12 September 1964) has been sequenced by Nhu Nguyen and falls in a different species of Suillus. This has to be re-extracted and re-sequenced.
  The MycoPortal records are under two names that need to be linked as synonyms. The two M.G.Weaver specimens at MICH are found under Fuscoboletinus weaverae. The one specimen at MIN is a split with MICH of MGW-1992 and found under Suillus weaverae.

TaxonomyPopulation size, distribution & trendsLife history & ecology

Use and Trade


Kretzer, A., Y. Li, T. M. Szaro, and T. D. Bruns. 1996. Internal transcribed spacer sequences from 38 recognized species of Suillus senu lato: Phylogenetic and taxonomic implications. Mycologia. 88(5):776-785.

McLaughlin, D. J.  Suillus weaverae. Minnesota Department of Natural Resources, Rare Species Guide:

McLaughlin, D. J. 1998. A search for three rare, endemic Minnesota mushroom species. A project report to the The Nature Conservancy and the Minnesota Department of Natural Resources.

Smith, A. H., and R. L. Shaffer. 1965. A new species of the Boletaceae. Michigan Botanist 4:27-30.


David J. McLaughlin
Department of Plant Biology
University of Minnesota
1475 Gortner Ave
Saint Paul, MN 55108

Else Vellinga

Country occurrence

Regional Population and Trends

Country Trend Redlisted