Suillus spraguei is a species of fungus in the family Suillaceae. It is known by a variety of common names, including the painted slipperycap, the painted suillus or the red and yellow suillus. Suillus spraguei has had a complex taxonomical history and is also frequently referred to as Suillus pictus. The readily identifiable fruit bodies have caps that are dark red when fresh, dry to the touch, and covered with mats of hairs and scales that are separated by yellow cracks. On the underside of the cap are small, yellow, angular pores that become brownish as the mushroom ages. The stalk bears a grayish cottony ring and is typically covered with soft hairs or scales. The species bears a resemblance to several other members of Suillus, including S. decipiens, but can be differentiated by variations in color and size. Suillus spraguei grows in a mycorrhizal association with several pine species, particularly eastern white pine, and the fruit bodies grow on the ground, appearing from early summer to autumn. It has a disjunct distribution, and is found in eastern Asia, northeastern North America, and Mexico throughout the range of the host tree. The mushroom is edible; opinions about its quality vary.
Taxonomy Suillus spraguei has a complex taxonomic history. The first specimen was originally collected in New England in 1856 by Charles James Sprague, and a formal scientific description was published in 1872 when Miles Joseph Berkeley and Moses Ashley Curtis called it Boletus spraguei. In a publication that appeared the following year, American mycologist Charles Horton Peck named the species Boletus pictus. Berkeley and Curtis had also described what they believed to be a new species—Boletus murraii—although this was later considered by Rolf Singer to be merely a younger version of their Boletus spraguei. Peck's description appeared in print in 1873, but the date stamp on the original publication revealed that he had sent his documents to the printer before the appearance of the 1872 Berkeley and Curtis publication, thus establishing nomenclatural priority under the rules of fungal naming. In 1945 Singer reported that the name Boletus pictus was illegitimate because it was a homonym, already being used for a polypore mushroom described by Carl Friedrich Schultz in 1806. The name was officially switched to Suillus spraguei in 1986 (Otto Kuntze had previously transferred the taxon to Suillus in 1898).
A 1996 molecular analysis of 38 Suillus species used the sequences of their internal transcribed spacers to infer phylogenetic relationships and clarify the taxonomy of the genus. The results indicate that S. spraguei is most closely related to S. decipiens. The species S. granulatus and S. placidus lie on a branch sister to that containing S. spraguei. These results were corroborated and extended in later publications that assessed the relationships between Asian and eastern North American isolates of various Suillus, including S. spraguei. The analysis supported the hypothesis that S. spraguei and S. decipiens in China and the United States were each other's closest relatives, and the clade that contained them could be divided into four distinct subgroups: S. decipiens, U.S. S. spraguei, China (Yunnan) S. spraguei, and China (Jilin) S. spraguei. The specific epithet spraguei is an homage to the collector Sprague, while pictus means "painted" or "colored". Suillus spraguei is commonly known as the "painted slipperycap", the "painted suillus", or the "red and yellow suillus". It is also called the "eastern painted Suillus" to contrast with the "western painted Suillus" (Suillus lakei).
Description The cap of the fruit body is 3 to 12 cm (1+1⁄4 to 4+3⁄4 in) in diameter, and depending on its age, is either conic to convex, to somewhat flattened at maturity. The cap margin is initially rolled downward before straightening out, often with hanging remnants of partial veil (appendiculate). The cap surface is covered with densely matted filaments that are rough and scale-like. The scales are pink to brownish red, fading to a pale brown-gray or dull yellow in maturity. Under the scales, the cap surface is yellow to pale yellow-orange. While many other Suillus species have a sticky or slimy cap, S. spraguei is dry. The flesh is yellow.
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