Introduction to Fungi, Third Edition

558 HOMOBASIDIOMYCETES
fungus is actually parasitic, and quite possibly it
is merely stimulated to fruit by the presence of
the earth ball.
Leccinum (75 spp.)
Like Boletus spp., the genus Leccinum has large
fleshy basidiocarps. A characteristic feature is
that the stem is covered with scales composed of
cystidia. Leccinum scabrum (brown birch bolete)
and L. versipelle (orange birch bolete) are common
ectomycorrhizal associates of birch (Betula).
Basidiocarps of Leccinum are generally edible.
19.5.3 Suillaceae
Suillus (90 100 spp.)
Suillus species have medium-sized fleshy basidiocarps
forming ectomycorrhizal associations with
conifers. Their fruit bodies are usually of yellowish
colours due to the abundance of pigments
derived from the shikimic acid pathway, especially
grevillins (Fig. 19.22d; Besl & Bresinsky,
1997). The cap may be dry and scaly but is more
usually viscid or slimy. There are species with a
ring on the stem (Fig. 19.21d), e.g. S. grevillei
(larch bolete) and S. luteus (slippery jack), whilst
in many others (e.g. S. bovinus, S. granulatus) there
is no ring (Plate 9g). The spores are smooth
and elongate, and pale brown to brown. The
presence of bundles of cystidia in the hymenium
is a feature which distinguishes this genus
from other boletes, and the classification into a
separate family is supported by phylogenetic
studies (e.g. Grubisha et al., 2001). Also included
in the Suillaceae are the gasteromycete genus
Rhizopogon (see p. 581) and the gill-bearing
Gomphidius.
The distribution of species mirrors that of
their mycorrhizal hosts, coniferous trees which
are largely confined to North-temperate regions,
only extending to other areas where introduced.
There is a fairly high degree of host specificity.
For example, in nature S. grevillei (Fig. 19.21d) is
almost exclusively associated with Larix spp.
(larch) whilst S. bovinus and S. luteus are associated
with Pinus spp. This ecological specificity is
probably associated with the effects of competition
because in the laboratory, under aseptic
conditions, a wider range of hosts has been
infected experimentally. Many species of
Suillus have edible basidiocarps and some areas
of planted pine (P. radiata) forests in South
America are devoted to production of S. luteus,
with astonishing annual productivity values of
up to 1 t dry weight ha 1 reported (Dahlberg &
Finlay, 1999). Suillus bovinus and S. variegatus are
common in Swedish pine plantations. Whereas
S. bovinus is an early-stage mycorrhizal fungus,
S. variegatus is often found in older stands.
In open communities dominated by seedling
pines, S. bovinus first develops a large number of
genets (genetically defined mycelial individuals)
derived from basidiospores. Once established,
a colony extends by mycelial spread and by
rhizomorphs to nearby host roots. The extent of a
genet can be estimated by evidence of somatic
incompatibility between mycelial isolates made
from basidiocarps. As the original genets expand,
they compete with each other. The number of
genets decreases, but as the genets increase in
size they may fragment so that parts of the same
genet may become separated. The maximum
rate of mycelial extension has been estimated to
be about 20 cm per annum and the age of the
largest genet to be about 75 years (Dahlberg &
Stenlid, 1990, 1994; Dahlberg, 1997).
19.5.4 Coniophoraceae
This group includes wood-rotting fungi such
as Serpula and Coniophora which form
spreading, crust-like resupinate fructifications.
Morphological characteristics suggested that the
Coniophoraceae have an affinity with Boletales
(Pegler, 1991), and Hibbett and Thorn (2001)
have included them in their bolete clade. This is
supported by the presence of pulvinic acids in
both Serpula and Coniophora (Gill & Steglich,
1987). Here we shall consider only Serpula.
Serpula
Serpula lacrymans (Figs. 19.21e,f) causes dry rot
and is one of the most serious agents of timber
decay in buildings. There is a very extensive
literature (see Rayner & Boddy, 1988; Jennings &
Bravery, 1991). Both hardwoods and softwoods
are attacked but, because softwoods are more
commonly used in building construction, it is on