Suillus americanus, also known as the Chicken Fat Bolete or the American slippery jack, is a native North American species of edible mushroom in the genus Suillus that is often found in close association with five-needled pine trees.
The taxonomic history of Suillus americanus is relatively straightforward, with its placement in the genus Suillus and family Suillaceae being well-established based on genetic and morphological data. This species was first collected and described during the period between 1860-1880 in New York by the American mycologist Charles Horton Peck. During this time, the species was listed under the name Boletus flavidus. Several decades later in 1931, the species was transferred to the now-defunct genus of Ixocomus (Ixocomus americanus) by the French mycologist Édouard-Jean Gilbert. Lastly, in 1969 Walter H. Snell in collaboration with Rolf Singer and Esther A. Dick once again transferred this species into its current genus and termed it Suillus americanus.
One additional point worth mentioning is that Suillus americanus has had several synonymous names and also, thanks to molecular DNA research incorporates several species which were once thought to be distinct. One of the most common synonymous names is Suillus sibiricus, which was also once thought to be distinct. Other synonyms, varieties, and forms which are all examples of S. americanus include S. himalayensis, S. flavoluteus, S. americanus var. reticulipes, S. americanus f. sibiricus, and S. americanus f. pseudosibiricus.
The etymology of this species’ scientific and common names are also straightforward. The epithet “americanus” means “of America”. While common names like the American Slipperycap and the American Slipper Jack refer to the distinctive sticky yellow cap with red to reddish brown markings that characterize Suillus americanus.
The characteristic physical features of Suillus americanus include a small to medium-sized cap with a mucilaginous, sticky surface covered with red to reddish-brown fibers and scales. The mushroom also has remnant tatters of the partial veil on its margins, and as it is a bolete, a distinctive yellow pore undersurface with angular pores. Another identifiable feature of this species is its strong association with eastern white pine trees.
Cap: The cap of this species measures 3-10 centimeters across. Young specimens have obtuse to convex caps with inrolled margins. However, as specimens age their caps become broadly convex or almost flat. The margins of the cap often have white to yellow-brown, cottony remnants of the partial veil material. The cap is bright to dull yellow in color and with age develops red to reddish brown stains or even scale-like plaques in very dry conditions. The surface of the cap is slimy and sticky, especially in young specimens.
Flesh: The flesh of S. americanus is thin. The cap flesh is yellow throughout. The flesh of the stem is also yellow, but slightly darker than the yellow flesh of the cap. The flesh may also stain a pinkish to purplish brown when cut or bruised.
Pores: S. americanus is a bolete, meaning that it has a porous cap undersurface rather than gills. The pores of this species are angular, somewhat radially arranged, and descend a small distance down the stalk. They are 1-3 mm in diameter at maturity and approximately 6-10 mm deep. Young specimens have yellow pores, while older specimens have yellow-brown or brown pores. Similar to the flesh, pores also bruise to a purplish brown color when damaged.
Stem: This species has a stem that measures 3-10 centimeters long. The shape of the stem is equally cylindrical but is often bent or crooked. It is yellow towards the apex, while towards the base it is more yellowish brown. The surface is also speckled with reddish brown dots. The stem may also occasionally have a ring or a ring zone. Like the flesh, the stem also bruises reddish brown. Lastly, the base of the stem is attached to its substrate by coarse, white to brownish rhizomorphs.
Spores: The spores of this species measure 8–10.12 by 3–5 µm in size. They are fusiform (nearly spindle-shaped) in shape and have a smooth surface.
Spore Print: The spore print of S. americanus is dull cinnamon to brown.
Smell: This species does not have a distinctive odor.
Flavor and Edibility: Suillus americanus is edible. This species is highly prized in Eastern Europe but is considered worthless by North American hunters due to its thin flesh. Dried specimens that have been reconstituted have a very rich, acidic, organ-like flavor.
Habitat: S. americanus is a mycorrhizal species that grows in sole association with 5 needled pines, also called white pines such as Pinus strobus, P. lambertiana, P. longaeva, and P. Monticola. They are usually found growing solitary or gregarious under these trees, often coming up through dense beds or masses of lichens or moss.
Range: This species has a large global distribution throughout the Northern Hemisphere. It can be found in India, Pakistan, Japan, China, Russia, Central and Eastern European countries, and North America. Within the continental United States, it is most commonly found from Maine down to North Carolina and as far west as Michigan.
Fruiting season: Commonly fruits from late summer to fall.
Suillus americanus is generally a distinctive mushroom, but there are some other species that may be mistaken for it. Some of the similar appearing species include:
- Suillus granulatus – this species has a buff cap and lacks veil
- Suillus brevipes – this species has a shorter and thicker stem.
- Suillus tomentosus – this species has a lighter-colored cap with a more velvety texture.
- Suillus pungens – this species has a scalier cap, thicker stem, and a more pronounced ring.
- Tylopilus felleus – this species has white pores on the underside of its cap.
One further point to mention. Most field guides list Suillus sibiricus as a distinct species from western North America and state that this species has a thicker stalk, and a ring, and is associated with western white pines. However as mentioned, modern molecular DNA research has shown that both species are most likely representatives of a single taxon.
Molecular research into the potential medicinal utilization of Suillus americanus has revealed that this species contains several compounds such as Beta-glucans and ergothioneine that are known to have anti-inflammatory and immunomodulatory properties. As such derivatives of this species may have future potential uses in reducing inflammation in conditions such as arthritis and inflammatory bowel disease, as well as in supporting the immune system in individuals with weakened immune systems.
Toxicity, Safety & Side Effects[vi]
Although Suillus Americanus is safe to consume there are some anecdotal reports of individuals experiencing contact dermatitis after handling this mushroom. Contact dermatitis may occur when the skin comes in contact with the slimy surface of the mushroom which may cause irritation or an allergic reaction in susceptible individuals. Symptoms and signs of contact dermatitis include redness, itching, swelling, and vesicular or blistering rash.
If you experience contact dermatitis after handling specimens of Suillus americanus it is best to avoid further contact with the mushroom and immediately cleanse the affected area with soap and water. If symptoms are severe or persist for a prolonged period of time individuals should seek medical care from a healthcare specialist.
[i] McKnight, K. H., & McKnight, V. B. (1987). American Slipperycap. In Peterson Field Guide to Mushrooms (pp. 113-114). Houghton Mifflin
[ii] Kuo, M. (2022, August). Suillus americanus.
[iii] Davis, R. M., Sommer, R., & Menge, J. A. (2012). Chicken-fat Bolete. In Field Guide to Mushrooms of western North America (pp. 581-582). University of California Press.
[iv] D. Arora (1986) Slipperjack In Mushrooms Demystified: A Comprehensive Guide to the Fleshy Fungi, Ten Speed Press, Berkeley (p. 498-499)
[v] Pacheco-Sanchez, M., Boutin, Y., Angers, P., Gosselin, A., & Tweddell, R. J. (2006). A bioactive (1–>3)-, (1–4)-beta-D-glucan from Collybia dryophila and other mushrooms. Mycologia, 98(2), 180–185.
[vi] Bruhn, J. N., & Soderberg, M. D. (1991). Allergic contact dermatitis caused by mushrooms. A case report and literature review. Mycopathologia, 115(3), 191–195.