Suillus collinitus is a pored mushroom of the genus Suillus in the family Suillaceae. It is an edible mushroom found in European pine forests. The mushroom has a reddish to chestnut-brown cap that reaches up to 11 cm (4.3 in) in diameter, and a yellow stem measuring up to 7 cm (2.8 in) tall by 1 to 2 cm (0.4 to 0.8 in) thick. On the underside of the cap are small angular pores, initially bright yellow before turning greenish-brown with age. A characteristic feature that helps to distinguish it from similar Suillus species, such as S. granulatus, is the pinkish mycelia at the base of the stem. Molecular analysis has shown the species to be related to other typical Mediterranean Suillus species such as S. bellinii, S. luteus, and S. mediterraneensis. S. collinitus is a mycorrhizal species, and forms associations with several species of pine, most notably the Aleppo pine. This tree species is commonly used in reforestation schemes and soil conservation against erosion in the Mediterranean region, and S. collinitus is often used as a beneficial inoculant to help the young trees better survive in typically harsh soil conditions.
Taxonomy, phylogeny, and naming
The species was first described as Boletus collinitus by Elias Magnus Fries in 1838. Otto Kuntze transferred it to the genus Suillus in his 1898 Revisio Generum Plantarum. In 1969 Dutch mycologist H.S.C. Huijsman described the variety S. collinitus var. aureus (as S. fluryi var. aureus; S. fluryi is a synonym of S. collinitus) based on a collection from Switzerland. The variety velatipes was described in 1998 by Giampaolo Simonini and colleagues from Italian collections. A 1996 molecular analysis of 38 different Suillus species used the sequences of their internal transcribed spacers to infer phylogenetic relationships and clarify the taxonomy of the genus. The results indicated that S. collinitus is most closely related to a specimen of S. granuatus collected from Nepal. According to the authors, this Nepalese isolate probably represents a species distinct from North American and European isolates, based on morphology and host tree association. In 2006, a phylogenetic analysis of Suillus isolates collected from Spain showed that S. collinitus was closely related to other species "typical of the Mediterranean area", namely S. bellinii, S. luteus, and S. mediterraneensis. The specific epithet collinitus is derived from Latin, and means "smeared" or "greased". The British botanist Mordecai Cubitt Cooke called the mushroom the "ringless yellow boletus" in an 1873 publication.
Description
The fruit body of Suillus collinitus is a medium to large, fleshy bolete. The cap is initially rounded, becoming convex and finally flat, reaching up to 11 cm (4.3 in) in diameter. The cap is covered with a brown cuticle of variable shade that is decorated with minuscule radial striations, which become more obvious in fully expanded specimens and especially in dry weather. The cap is often shaped irregularly and becomes viscid (sticky) when damp. The tubes are short and their stem attachment is usually slightly decurrent to adnate. The small and angular pores are yellow but darken with age. Young, fresh specimens sometimes bear droplets of a clear fluid that collect on the pore surface. The cylindrical stem is often short and stubby, typically 4–7 cm (1.6–2.8 in) tall by 1–2 cm (0.4–0.8 in) thick, coloured yellowish and ornamented with sparse reddish-brown granules. There is no ring. The base of the stem bears pink overtones and is attached to distinctively pink mycelial threads, which are visible when the fruit body is uprooted. The flesh is yellowish, thick and soft. In a colour reaction test with ammonia solution, the flesh turns reddish. The spores are seen ochre-brown in mass, but pale yellow when viewed with a light microscope. They are fusiform (tapered at each end), sized 8–10.5 by 3–4.5 μm. The basidia (spore-bearing cells of the hymenium) are four-spored.
Especially characteristic for S. collinitus are the cap striations and pink mycelium. The fungus in many aspects resembles S. granulatus – a common species in European pine forests. S. granulatus, however, has a homogeneous brown cap without striations, and its mycelium is characteristically white.
Varieties Two varieties of S. collinitus have been described. S. collinitus var. aureus has a golden-yellow cap. S. collinitus var. velatipes, originally found in Italy growing in poor acidic soil in association with Aleppo pine (Pinus halepensis), is distinguished by a glutinous brown veil at the base of the stem, and a slender white felting at the cap margin.
Similar species Suillus collinitus is often found in the same habitat with other thermophilic species, including S. mediterraneensis and S. bellinii, especially in the Mediterranean basin. Some common species which occur throughout much of Europe and also associate with two-needled pines include S. luteus and S. granulatus.
Edibility Various authors regard Suillus collinitus as edible with a sour odor and nondescript taste. It is advisable, as for all species of Suillus, to pick only young specimens and to peel the cuticle before preparation. The mushroom contains several tocopherols, a class of chemical compounds collectively known as vitamin E, and which confer antioxidant activity. They also contain several organic acids, most predominantly the pairs malic and quinic acids, and citric and ketoglutaric acid, which respectively make up 42% and 30% of total organic acids. The composition and concentration of organic acids in mushrooms are major factors in influencing their flavour; some organic acids contribute to antioxidant activity.
Distribution, habitat, and ecology
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