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Suillus occidentalis
Suillus occidentalis photographed by Nhu Nguyen, August 18, 2017 near Gold Hill, Colorado.

Suillus occidentalis

Suillus occidentalis Thiers is a mutualistic ectomycorrhizal mushroom-forming fungus that exchanges soil mineral nutrients for photosynthates from its host. The species associates with two-needle pines (Subgenus Pinus) hosts. The species is commonly associated with Pinus contorta and Pinus ponderosa in the Southwestern United States on maturing pines. It appears to have a broad distribution based on morphologically similar looking specimens from California and Mexico, although these specimens have not been confirmed with DNA sequences. The original morphological description of the holotype (Thiers 1976) specifically mentioned that fibrils and annulus are not present, but sequencing of the holotype and specimens by independent labs suggests that the specimens with abundant fibrils and often with a thin annulus (sometimes absent) belong to the same species (Nguyen et al. 2016). Not much is known about its autecology.

Suillus as a genus is one of the most common ectomycorrhizal symbionts of the pine family (Pinaceae) in the northern hemisphere. Commonly known as ‘Slippery Jacks’, the mushrooms of this genus provide food for both wildlife and humans. Suillus species have been used in forest restoration following natural and human-made disturbances, have potential for bioremediation (mycoremediation), and likely play an important role in facilitating soil carbon sequestration in mycorrhizal forests.

This genome is part of the Community Science Program (Proposal 502931) “A genome atlas of the ectomycorrhizal genus Suillus: Phylogenetic diversity and population genomics of a keystone guild of symbiotic forest fungi”, a collaborative effort aimed at using genomics data to understand and connect the evolutionary history, ecology, and genomic mechanisms of mutualistic ectomycorrhizal symbionts and their Pinaceae hosts. Please contact the PI for permission prior to the use of any data in publications.


Thiers HD. 1976. The boletes of the Southwestern United States. Mycotaxon 3:261–273.

Nguyen NH, Vellinga EC, Bruns TD, Kennedy PG. 2016. Phylogenetic assessment of global Suillus ITS sequences supports morphologically defined species and reveals synonymous and undescribed taxa. Mycologia 108:1216–1228, doi:10.3852/16-106.

Genome Reference(s)