Suillus collinitus (Fr.) Kuntze

Phylum: Basidiomycota - Class: Agaricomycetes - Order: Boletales - Family: Suillaceae

Boletus collinitus

Suillus collinitus occurs beneath pine trees and is most commonly found in southern European countries, particularly where large pines provide shade in otherwise dry sandy soils. This edible bolete often occurs in large groups.

Only infrequently is this warm-climate bolete seen in Britain, where from 2002 until 2006 it was considered to be 'vulnerable' and included on the Red Data List. Even nowadays it is a rare find with only three officially recorded sightings in Scotland.

Distribution

Many of the locations where Suillus collinitus occurs in Wales are sandy coastal sites, such as Newborough Warren on Anglesey and Whiteford Borrows on the Gower Peninsula; however, In England this bolete has been found in many inland sites in the Midlands and the Home Counties as well as in many sites in East Anglia and along the south coast.

Suillus collinitus, mature fruitbody

Along the sandy cliff tops of southern and south-western Europe, including some parts of the Mediterranean shoreline, Stone Pines and other drought-tolerant members of the genus Pinus provide small oases of shade where Suillus collinitus plays a vital role in supporting the trees beneath which it occurs often in large numbers. Like nearly all of the boletes, this large mushroom is mycorrhizal, supplying its tree partners with water and trace elements scoured from the soil around the tree. In exchange, the pine trees share the energy-rich sugary products of photosynthesis with their fungal partners. The structures at the tips of a tree's root systems, where fungal hyphae form coral-like sheaths around the fine tree rootlets, are known as mycorrhizae - literally 'fungus-roots'. Pines could not thrive (or in many cases even survive) in such harsh environments without the support of mycorrhizal partners... and vice versa.

Suillus collinitus, mature fruitbody

You will never find Suillus collinitus where there are no trees, but when pine plantations are being created in areas of poor or contaminated soil, foresters often inoculate the roots systems of tree seedlings with a mycorrhizal paste made from suitable fungi (for example, Pisolithus arrhizus) to give the new woodland a kick start. More and more fungal species will appear progressively as the trees grow larger, but Suillus collinitus is one of the many mycorrhizal fungi that are latev arrivals, being most commonly associated with mature trees.

Taxonomic history

When in 1838 Elias Magnus Fries described this species he named it Boletus collinitus, and it was transferred to its current genus Suillus in 1898 by German botanist Otto Kuntze (1843 - 1907). Other synonyms for this species include Boletus collinitus Fr., and Suillus fluryi Huijsman.

Etymology

The specific epithet collinitus is derived from Latin and means 'smeared' or 'greased', while the generic name Suillus is very straightforward, coming from the Latin noun sus, meaning pig, Suillus therefore means of pigs (swine) and is a reference to the greasy nature of the caps of nearly all fungi in this genus.

Identification Guide

Cap of Suillus collinitus

Cap

Initially hemispherical, becoming convex and eventually flat, caps of Suillus collinitus typically range from 4 to 12cm when fully expanded, but exceptional specimens to 18cm can be found occasionally beneath large pines in well-shaded sites. Although starting off roundish, most caps become slightly irregular or even lobed, and the margin is often wavy. Tufts of fruitbodies inevitably develop distorted caps, sometimes with pores on one side flaring upwards while on the opposite side they remain below ground level. The peelable cap cuticles, which are very viscid in wet weather, are various shades of brown, often with faint radial striations most noticeable near the margin.

Pores of Suillus collinitus

Tubes and Pores

Beneath the cap, the fertile surface comprises short tubes, adnate or very slightly decurrent to the stem, terminating in small angular pores that are initially creamy yellow, becoming bright yellow and then taking on a brownish tinge as they age. In well-shaded sites, droplets of a clear liquid appear on the pore surface of young specimens. (Pores of the similar Suillus granulatus, which is more common in northern Europe, exude a milky liquid.)

Stem of Suillus collinitus

Stem

Stems of Suillus collinitus are cylindrical and short (3 to 7cm long and typically 1 to 1.8cm in diameter), pale to medium yellow along most of their length but with rounded bases that are a distinctly pinkish yellow, the pink tone coming from the mycellium of this species, which is pink rather than white as in most other Suillus species. (This feature helps differentiate Suillus collinitus and the otherwise very similar Weeping Bolete Suillus granulatus.)

Small reddish-brown granules ornament the surface of the ringless stem, whose interior flesh is creamy yellow.

Spores of Suillus bovinus

Spores

Subfusiform, slightly tapering to one end, smooth, 8-10.5 x 3-4.5μm.

Show larger image

Spore print

Ochre-brown.

Odour/taste

Odour fungal but not distinctive; taste mild.

Habitat & Ecological role

Ectomycorrhizal with pines in forests, parks and gardens and on coastal cliff tops.

Season

September to November in Britain and Ireland; from October to February in southern Europe.

Similar species

Suillus granulatus  has milky droplets beneath its young caps and white (rather than pink) mycelium at its base.

Suillus luteus is similar in general appearance and favoured habitat but it has a large white stem ring.

Culinary Notes

Although not generally rated very highly, Suillus collinitus is reported to be edible when thoroughly cooked. To reduce the risk of an adverse reaction to these mushrooms some people have found it advisable to discard the cap skin of all species from the Suillus genus.

Reference Sources

Fascinated by Fungi, Pat O'Reilly 2016.

British Boletes, with keys to species, Geoffrey Kibby (self published) 3rd Edition 2012

Roy Watling & Hills, A.E. 2005. Boletes and their allies (revised and enlarged edition), – in: Henderson, D.M., Orton, P.D. & Watling, R. [eds]. British Fungus Flora. Agarics and boleti. Vol. 1. Royal Botanic Garden, Edinburgh.

BMS List of English Names for Fungi

Dictionary of the Fungi; Paul M. Kirk, Paul F. Cannon, David W. Minter and J. A. Stalpers; CABI, 2008

Taxonomic history and synonym information on these pages is drawn from many sources but in particular from the British Mycological Society's GB Checklist of Fungi and (for basidiomycetes) on Kew's Checklist of the British & Irish Basidiomycota.

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