The molecular systematics of the Western U.S. edible ectomycorrhizal
mushrooms in the Boletus edulis complex, Boletus section Edules.
The Boletus edulis species complex
is probably the most widely sought after group of edible mushrooms in
the world. Because of this popularity many cultures have given these
mushrooms common names; such as Steinpilz (German), porcino
(Italian), cepe de Bordeaux (French), penny bun (English), zhutui mo
(Northern Chinese), and dajiao gu (Southern Chinese). These species
are responsible for millions of dollars in commerce each year. These
mushrooms have avoided many attempts to be cultivated. They are only
collected for comsumption from natural forests and woodlands, where
they must form mutualistic mycorrhizal associations with trees. Probably
because they are all edible, several distinct species are often lumped
under Boletus edulis. Although they may all be considered B. edulis, the
different species can have different values on the market. For example,
mushrooms from Italy are considered gastronomically better and are
more expensive that those from China. This difference in culinary
qualities is almost certainly explained by different species in each
region. The unifying features that distinguish this group of mushooms
(Boletus section Edules) are the pored hymenium (spore producing
tissue), reticulate stipe, white membranous tissue covering the pores
early in the development of the mushroom, and the mild raw taste. The
goal of this research is to investigate and understand the biology
(taxonomy, systematics, ecology, and physiology) of the species in the
Boletus edulis complex. The results presented here define the Western
North American species.
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Boletus mottiae Thiers
Usually misidentified as B. aereus Bulliard: Fr.,
which is a European species
Type locality: Grass Valley, Nevada Co. California
Habitat: In oak, madrone, and mixed woodlands in the foot hills of
the Sierra Nevada, Cascades and thoughout the coastal mountains.
Host tree (potential): Quercus species, Pinus species,
Pseudotsuga menziesii, Arbutus menziesii, Chrysolepis chrysophylla,
Lithocarpus densiflorus
Distribution: Known from the coastal mountains of California from San
Mateo Co. north to the coastal mountains of Oregon to Lane Co. Also
occuring on the western foothills of the Sierra Nevada and North to
the Oregon Cascades, Lane Co. Possibly throughout the Kalamath
mountains and probably up to Washington and British Columbia, Canada.
Phenology: Late Fall, October throught December.
Boletus sp. nov. (Spring King)
Gastroboletus subalpinus Trappe & Thiers
Habitat: Montane coniferous forests of the Sierra Nevada,
Cascades, and Rocky Mountains of Idaho.
Host tree (potential): Abies species and Pinus species.
Distribution: Southern Sierra Nevada, Fresno Co. north
to Descutes Co. in the Oregon Cascades probably
extending into Washington and British Columbia,
Canada. Also know from Idaho.
Phenology: Spring, May and June.
Boletus edulis Bulliard: Fr.
Type locality: France
Distribution: Throughout the Northern
In Western North American
This tree
is an unrooted branch
and bound parsimony
analysis of 4 genetic loci:
chitin synthase, GPD,
ITS, and IGS. Bootstrap
values are on the
branches. Other
analyses not shown
suggest that the root
should be on the longest branch.
10 0
Habitat: Coastal and Montane moist coniferous
forests. Also Hardwood riparian forests of the
Willamette Valley.
Host tree (potential): Picea species, Pinus
species, Abies species, Populus balsamifera
spp. trichocarpa
Distribution: Along the Coast the most southern
collection is from Monterey Co. In the mountains it is reported as far
south as Fresno Co. in the Sierra Nevada. It may extend farther south.
To the north it extends up to Alaska and east into the Rocky Mountains.
Phenology: In Montane habitats it may fruit in mid August until October.
On the Coast it may be fruiting in mid September through November
with one reported fruiting in the Southern end of the range in early March.
Boletus fibrillosus Thiers
Type locality: Cloud Cap, Hood River Co. Oregon
Habitat: Montane coniferous forests of the Oregon Cascades and the
California Seirra Nevada mountains
Host tree (potential): Abies species, Pinus species, Tsuga mertensiana
Distribution: Northern limit is just south
of the Columbia River in the Oregon
Cascades, Hood River Co, extending
South through the Cascades into the
Seirra Nevada of California all the
way to Fresno Co. One collection is
known from the Kalamath Mountains
Phenology: August in the southern
portion of the range and September
and October in the northern areas.
Department of
Plant and Microbial Biology
University of California, Berkeley
Francisco J. Camacho
& Tom Bruns
CI = 0.897
= 174
Boletus aestivalis (Paulet) Fr.
NOT in Western North America
Type locality: Europe
Host tree (potential): Fagus species and
Quercus species
Distribution: Europe and Asia
Phenology: summer and early autumn
The Western North America Boletus edulis complex
There are six species in Boletus section Edules in Western North America. With the exception of
Boletus edulis, the five other species are endemic to this region. One species, the Spring fruiter,
appears to be unnamed. Western North America has a high abundance of coniferous forests and
these species are all associated with some of the different dominant trees found these forests.
Boletus barrowsii and B. mottiae can also be associated stricktly with hardwood trees. Except for B.
edulis and B. fibrillosus, these species have adapted to different niches in Western North America.
Boletus edulis and B. fibrillosus occur along the coast and in higher montane regions. In both of these
habitats they can be found sympatrically fruiting in late summer through the Fall. Although B. fibrillosus
appears to be less common and more limited in distribution than B. edulis. Boletus barrowsii is mostly
a southwest species fruiting in August and September with oaks and ponderosa pine. Gastroboletus
subalpinus (soon to be placed in the genus Boletus) has a similar phenology, fruiting in summer and
early fall. This species has a distinctive fruitbody which is contorted with the pores not aligned
perpendicular to the ground, preventing easy air dispersal of spores. Gastroboletus subalpinus is
limited to the Sierra Nevada and Cascade mountains. Boletus mottiae has long been missidentified
as the European species B. aereus. This species fruits later in the Fall well after the rains have come.
It occur in the coast range, but not on the coast like B. edulis, and in the foothills (not the high
elevations) of the Sierra Nevada and Cascades. The remaining Boletus species, the Spring King,
fruits in the spring and occurs in the Sierra Nevada and Cascade mountains. Although the knowledge
of the distribution of these endemic species still needs much work, the Sierra Nevada mountains
appears to be the center of diversity were there may have been a refugium durring the last major glacial
period. Possibly some of these species are migrating Northward since the late Pleistocene.
Type locality: Jackson State Forest, Mendocino Co. California
Habitat: Coastal and Montane moist coniferous forest of the Western U. S.
Host tree (potential): Abies species, Pinus species, Picea speices,
Pseudotsuga menziesii, Quercus species
Distribution: Along the west coast from Lincoln Co. Oregon in the north
and Santa Cruz Co. California in the south. In the Cascades from Linn
Co. Oregon in the north to the Sierra Nevada Tuolumne County
in the south. Also known from one montane site in the Oregon Coast
Range on Mary's Peak, Benton Co. Oregon. Probably extends into
Washington and British Columbia, Canada.
Phenology: Late August to October in the Sierra Nevada and Cascades,
October and November during the rainy season along the coast, and
October and November in the Oregon Coast Range.
Boletus barrowsii Thiers & Smith
Type locality: Jacob Lake, Kaibab National Forest, Coconino Co. Arizona
Habitat: Coastal live oak and mixed coniferous and hardwood forests of montane areas.
Host tree (potential): Pinus species, Abies species, Quercus species.
Distribution: In California it is reported from
coastal areas from Marin Co. to the island Santa
Rosa in the Channel Islands. It probably extends
to the southern reaches of California, San Diego
Co. and into Mexico. It is found east through
Arizona and New Mexico. As far South as
Mexico and north from New Mexico, through
Colorado and into Idaho.
Phenology: California coastal speciems have
been collected in May and November, montane
collections are found in August.
The climate of Western North America
is characterized by dry summers. These dry summer conditions place adaptive pressures on
mushrooms which can quickly lose water, shrivel up and thus not produce spores and offspring.
Boletus fibrillosus, B. mottiae, Gastroboletus subalpinus, and the Spring King probably evolved
in this region. They appear to have develped different adaptations to dealing with summer drought.
Boletus fibrillosus which most closely resembles the potential ancestral adaptations of B. edulis
occurs in moist habitats in higher montane areas and near the moist fog-influenced coast. In these
areas temperatures are not high and evaporative water loss from mushrooms is less. The closest
relative of B. fibrillosus is the Spring King which fruits in the spring when temperatures are cooler
and there is plenty of soil moisture from snow melt. Boletus mottiae occurs in drier habitats but it
fruits later in the Fall when there is pleanty of rain and more humidity to avoid dessication. It's
closest relative is G. subalpinus which does fruit in the summer in dry habitats, but it fruits
underground where it is protected from evaporation. These four mushroom species have each
evolved unique ways of dealing with the environment they live in.
We would like to thank the following people who helped with this project
Jamie L. Platt, Erik Lilleskov, Jenny Tan, Lauren Thompson, Rasmus Kjoller, LIsa Grubisha,
Lisa Bauer, Tom Horton, Martin Bidartondo, Anna Levin, Bruns and Taylor Lab,
Dennis Desjardin and the Harry D. Thiers Herbarium.
Funding was provided by Novartis

Boletus fibrillosus - University of California, Berkeley