SPECIES FACT SHEET
Scientific Name: Rhizopogon exiguus Zeller
Division: Eumycota
Subdivision: Basidiomycotina
Class: Gasteromycetes
Order: Hymenogastrales
Family: Rhizopogonaceae
Conservation Rankings and Status:
Global: G2G3
State: OR S1S2, WA Not ranked
Oregon Biodiversity Information Center (ORBIC) List 2
(Ranks from ORBIC, http://orbic.pdx.edu accessed August 16, 2013)
Type Locality: Pierce County, Washington
Type: Zeller 8278
Originally described by Zeller (1939) from Pierce Co., Washington. There are no
known synonyms.
Technical Description: Rhizopogon exiguus is characterized by a farinaceous
odor, long basidia, and the bright reddish brown spores and peridium when
mounted in KOH
Fruiting body 2-10 mm broad, globose or nearly so, lobed in large specimens,
consistency soft and spongy, surface smooth, white with ochraceous mottling,
becoming snuff-brown, fibrils scanty above, rhizomorphic below. Gleba white
then brown, concolor with peridium as dried in mature specimens, cavities
small, rounded, partly filled with spores. Odor farinaceous. Spores 7-8 x 5-5.5
µm, oval to elliptic and base truncate from broad basal scar, yellowish
individually as revived in KOH and rusty cinnamon in mass, in Melzer's
reagent yellowish to rusty yellowish, wall smooth and slightly thickened.
Basidia 20-40 x 6-7.5 µm, narrowly clavate, walls may be thickened slightly as
well as colored pale cinnamon (revived in KOH). Paraphyses 14-20 x 7-10 µm,
hyaline, thin-walled, nongelatinous. Cystidia none seen. Tramal plates of
hyaline refractive hyphae, not obviously gelatinous, subparallel to interwoven,
subhymenium of branched filaments. Peridium a single layer of compactly
interwoven hyphae in mass bright rusty cinnamon in KOH, at the exterior with
loosely interwoven hyphae yellowish in KOH but not forming a distinct epicutis,
hyphae thin-walled or walls very slightly thickened. Clamp connections
absent. All tissues non-amyloid.
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Rhizopogon is one of several genera included among the “false truffles.” There
are perhaps four groups of fleshy fungi with which species of Rhizopogon are
likely to be confused: 1) puffballs, 2) gastroid agarics, 3) other “false truffle”
genera, and 4) true truffles. False truffles, puffballs, and gastroid agarics are
included within the Gasteromycetes – basidium-producing fungi whose spores
are produced internally and not forcibly discharged from the basidia. The spore
mass of puffballs (Lycoperdon and allies) is usually white, firm, and without
readily discernable chambers when young, and becoming powdery and rather
quickly dispersed at maturity. The fruiting bodies of puffballs are usually found
aboveground. While the presence of a cap and stalk is clearly evident in some
gastroid agarics, species of Endoptychum, Brauniellula or Thaxterogaster may
bear a stronger resemblance to false truffles. However, dissection of a gastroid
agaric will reveal at least some evidence of a percurrent stalk (one that extends
through the spore mass to the top of the cap). At maturity, the sporocarps of
gastroid agarics are usually found partially or fully aboveground. Among other
genera of false truffles (e.g., Alpova, Gautieria, Hydnangium, Hymenogaster,
Hysterangium, Leucophleps, Martellia and Truncocolumella), Rhizopogon
generally is distinct in exhibiting the following set of features: 1) an exterior
surface often overlain with soft mycelial strands (rhizomorphs), 2) spore mass
composed of minute, generally non-gelatinous chambers (best seen with hand
lens), 3) stalk (basal and within spore mass) typically lacking and 4) spore
surfaces smooth. Microscopically, true truffles are readily differentiated from
species of Rhizopogon by the presence of sexually produced spores borne within
asci. Macroscopically, however, fruiting bodies of true truffles will, as is
typically true of Rhizopogon, show no evidence of a stalk, either basal, or within
the spore mass. The interior of a true truffle, however, will typically differ from
that of Rhizopogon species in being either 1) solid and marbled with veins, or 2)
completely hollow or with quite evident folds and chambers. Because of the
need to recognize multiple, subtle, microscopic anatomical features and use
chemical staining procedures, it is probably unrealistic to expect a lay
mycologist to do more than recognize that a fleshy fungus specimen is likely to
be included in the genus Rhizopogon. Identification to species will almost
certainly require the services of a Rhizopogon "expert".
Life History: Fruits in March, August, September, and November. This
species is ectomycorrhizal with Pseudotsuga and Tsuga and probably other
Pinaceae. It likely depends on mycophagy (consumption by animals) for spore
dispersal.
Range, Distribution, and Abundance: Known from 7 sites in the Northwest
Forest Plan area in Washington and Oregon. Sites are located in the Western
Cascades and Eastern Cascades Physiographic Provinces in Washington and
the Coast Range and Klamath Mountains Physiographic Provinces in Oregon.
One site each has been documented in the Okanogan-Wenatchee National
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Forest, Mt. Baker-Snoqualmie National Forest, Rogue River-Siskiyou National
Forest, Siuslaw National Forest, and Medford District BLM/Grants Pass
Resource Area. One site was documented 1,800 m. southeast of the Rogue
River-Siskiyou National Forest. There were no detections of this species during
Random Grid CVS/FIA plot surveys.
FS/BLM lands where documented: Okanogan-Wenatchee National Forest, Mt.
Baker-Snoqualmie National Forest, Siuslaw National Forest, Rogue RiverSiskiyou National Forest, Medford District BLM/Grants Pass Resource Area.
Habitat Associations: Four sites have been documented in the Douglas-fir
series/wet Douglas-fir habitat association. One site each has been documented
in the white fir/grand fir series/moist white fir/grand fir habitat association,
western red cedar series/wet western red cedar association, and western
hemlock series/western hemlock wetlands. The elevation of the sites ranges
from 16 m. (54 feet) to 1,172 m. (3,844 feet), with a mean of 658 m. (2,159
feet).
Threats: With the assumption that this species is ectomycorrhizal, it is
reasonable to assume that as with ectomycorrhizal fungi in general, threats to
the species are activities or events that result in direct or indirect impacts to
fungal individuals or mycelial mats. These threats include activities that:
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remove or destroy the fungal organism
intensively or extensively remove or consume the woody substrate, forest
floor litter, or tree or shrub hosts with which the species is associated
remove trees or other vegetation that significantly modifies the
microclimate at the species’ site
compact soil or change soil chemistry
Impacts to fungal organisms can reduce both the biomass and species diversity
within a community of ectomycorrhizal fungi. Attendant reductions in
production of false truffles may, in turn, potentially reduce dispersal of their
spores by small mammals. Fire is a potential threat to Rhizopogon exiguus
because it occurs in mid-elevational, somewhat dry forests where fire has
traditionally been more common. Climate change may result in a decline of
vigor and may result in extirpation of this species. An increase in temperature
or a decrease in precipitation could affect disjunct populations.
Conservation Considerations: Revisit documented sites to reconfirm
presence and better define habitat. Conduct surveys to locate new populations
on federal land. Buffer known sites and protect from wildfire; prescribed burns;
vegetation management projects that would remove potential host plants,
disturb soil or duff, or change habitat or microclimate conditions; and grounddisturbing activities (e.g., recreational vehicles, road building, grazing) that
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would reduce moisture-retaining ground covers. Consider vegetation
management activities within known site buffers that are likely to maintain or
improve ectomycorrhizal fungal habitat quality (e.g. moderate hand-thinning of
an overstocked stand or augmenting a deficient volume of coarse woody
debris). When conducting vegetation management activities in areas with good
habitat potential, consider leaving scattered and clumped host trees and ample
coarse woody debris while minimizing soil compaction and burn severity of
activity-related fires.
As a mycorrhizal species, Rhizopogon exiguus forms symbiotic associations
with the fine root systems of plants, growing out into the soil matrix. Consider
incorporation of patch retention areas (as described in Standards and
Guidelines 1994, C-41) with occupied sites wherever possible.
Other pertinent information (includes references to Survey Protocols,
etc): The survey protocol for fungi is located on the ISSSSP website:
http://www.fs.fed.us/r6/sfpnw/issssp/documents/inventories/inv-sp-fuver1-2008-12.pdf.
The survey protocol for Survey and Manage fungi is located on the Survey and
Manage website: http://www.blm.gov/or/plans/surveyandmanage/protocols/
Prepared by: Marcia Wineteer, Medford BLM
Date: April 2013
Edited by: Rob Huff, BLM/FS Portland, Oregon
Date: February 2014
ATTACHMENTS:
(1)
References
(2)
Map of Species Distribution
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ATTACHMENT 1:
References
Arora, David. 1979. Mushrooms Demystified – A Comprehensive Guide to the
Fleshy Fungi. Ten Speed Press, Berekeley, California. 959 pp.
Castellano, Michael A. and Thomas O’Dell. 1997. Management
Recommendations for Survey and Manage Fungi. Version 2.0.
Castellano, Michael A., Jane E. Smith, Thom O’Dell, Efren Cazares, and Susan
Nugent. 1999.Handbook to Strategy 1 Fungal Species in the Northwest Forest
Plan. General Technical Report PNW-GTR-572.
Cushman, Kathleen and Rob Huff. 2007. Conservation Assessment for Fungi
Included in Forest Service Regions 5 and 6 Sensitive and BLM California,
Oregon and Washington Special Status Species Programs. R6 USFS and
OR/WA BLM Interagency Special Status/Sensitive Species Program (ISSSSP).
http://www.fs.fed.us/r6/sfpnw/issssp/planning-tools/
Dewey, Rick and Jennifer Ferriel. 2007. Habitat Summary for Sensitive Fungi
Species.
http://www.fs.fed.us/r6/sfpnw/issssp/species-index/flora-fungi.shtml
Ferriel, Jenifer and Katie Grenier. 2008. Annotated Bibliography of Information
Potentially Pertaining to Management of Rare Fungi on the Special Status
Species List for California, Oregon and Washington. R6USFS and OR/WA BLM
Interagency Special Status/Sensitive Species Program (ISSSSP).
http://www.fs.fed.us/r6/sfpnw/issssp/planning-tools/
Oregon Biodiversity Information Center. 2010. Rare, threatened and
endangered species of Oregon. Oregon Biodiversity Information Center,
Institute for Natural Resources, Oregon State University, Portland, Oregon.
105pp.
http://orbic.pdx.edu/documents/2010-rte-book.pdf
Smith, Alexander H. and S.M. Zeller. 1966. A Preliminary Account of the North
American Species of Rhizopogon in Memoirs of The New York Botanical
Garden, Vol. 14, No. 2, March 15, 1966.
Trappe, James M., Randy Molina, Daniel L. Luoma, Efren Cazares, David Pilz,
Jane E. Smith, Michael A. Castellano, Steven L. Miller, and Matthew J. Trappe.
Diversity, Ecology, and Conservation of Truffle Fungi in Forests of the Pacific
Northwest. 2009. PNW-GTR-772. 202 pages.
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ATTACHMENT 2:
Map of Species Distribution
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