Introduction to Fungi, Third Edition

556 HOMOBASIDIOMYCETES
Fig19.21 Basidiocarps in the boletoid clade. (a) Paxillus involutus. Note the inrolled cap margin and decurrent gills.The fruit
bodies shown here have been attacked by the parasitic mould Sepedonium chrysospermum (white patches). (b) Boletus (Xerocomus)
chrysenteron.(c)Boletus edulis, the cep or penny bun. (d) Suillusgrevillei, an ectomycorrhizal associate of Larix.Notethering
on the stem. (e,f) Serpula lacrymans, the dry rot fungus. (e) Beam supporting the roof of a church showing the typical
cracking transverse to the grain of the wood which also shows shrinkage. (f) Resupinate fruit body on a ceiling showing the
shallow pores.
Spread through the soil to fresh young roots is
by an effuse mycelium or by rhizomorphs.
The fungus may survive in the soil by means of
sclerotia. Some isolates are capable of saprotrophic
growth and can fruit in the absence of a
mycorrhizal host. Affinity with the Boletales has
long been suspected because basidiocarps of P.
involutus are commonly attacked by the bright
yellow conidial state (Sepedonium chrysospermum)
of the mycoparasitic ascomycete Apiocrea chrysosperma,
which also attacks different boleti and
gasteromycetes believed to be related to them
(Fig. 19.21a; Plate 9h; p. 581).
The basidiocarps of P. involutus, although traditionally
considered edible, are, in fact, poisonous.
There are two symptoms. A heat-labile substance