Introduction to Fungi, Third Edition

542 HOMOBASIDIOMYCETES
edible and several species, e.g. P. ostreatus and
P. sajor-caju, are widely cultivated. Ligno-cellulosic
waste products from a range of agricultural
crops (e.g. wheat, rice, maize straw, banana
leaves and dried water hyacinth) and industrial
extraction processes can be used as substratum
and cultivation can be practised in factories as
well as on a smaller scale, e.g. in large cylindrical
plastic bags in the context of a ‘cottage industry’
which can provide a valuable food supplement
in developing countries (Poppe, 2000; Sánchez,
2004). Spent substratum can be used for
further fungal fermentations or as animal
feed. A problem with the cultivation of Pleurotus
spp. is the massive amount of basidiospores
released from an early developmental stage
onwards, causing ‘mushroom worker’s lung’.
In order to overcome this problem, sporeless
mutants have been bred.
Pleurotus ostreatus, one of the best-known
species, forms clusters of fan-shaped, bluishgrey
basidiocarps at the base of deciduous tree
stumps (Fig. 19.14e), especially beech (Fagus
sylvatica). The gills are decurrent (running down
the base of the stipe). Development in P. ostreatus
is gymnocarpic and construction monomitic, but
in some other species, e.g. P. tuberregium, skeletal
hyphae are present. Some species develop
thallic arthric anamorphs, e.g. P. cystidiosus in
which the conidiophores are synnematal. In
addition to being able to decompose wood,
P. ostreatus and some related species are nematophagous
(Barron & Thorn, 1987; Hibbett & Thorn,
1994; Thorn et al., 2000; see p. 679), and the
nematode prey represents an important supplement
of nitrogen which is often the growthlimiting
nutrient in woody substrata. The
ability to parasitize nematodes has been used
as a criterion to support the classification of
P. tuberregium, a tropical species whose basidiocarps
arise from large subterranean sclerotia
(Hibbett & Thorn, 1994).
Hohenbuehelia (50 spp.)
This genus includes terrestrial lignicolous
species. The basidiocarps frequently contain
gelatinized tissue. All species are nematophagous.
Nematodes are trapped on hourglassshaped
(i.e. constricted) knobs covered with a
toxic secretion, formed either directly on the
clamped mycelium or at the tips of bent, tapering
conidia assigned to the anamorph genus
Nematoctonus (Barron, 1977; Barron & Dierkes,
1977; see Fig. 25.7).
19.4.6 Schizophyllaceae
Although the unique pattern of fruit body and
gill morphogenesis seemed to set Schizophyllum
clearly apart from the Agaricales (Donk, 1964),
the euagarics clade is where we must now
place it on the basis of DNA analyses (Moncalvo
et al., 2002). More confusingly still, the two fungi
apparently closest to Schizophyllum are the
polypore Fistulina and the gill-bearing genus
Volvariella.
Schizophyllum
Schizophyllum commune has a worldwide distribution
but is more common in warmer regions.
It grows saprotrophically or parasitically on a
wide range of woody substrata forming beigecoloured,
fan-shaped, laterally attached fruit
bodies with a furry upper surface. Since 1990 it
has become common in Western Europe on
plastic-wrapped hay silage bales from which
clusters of basidiocarps burst out (Fig. 19.16a;
Brady et al., 2005). Its spores are wind-borne.
James and Vilgalys (2001), working in the
Caribbean, trapped spores sedimenting onto
the surface of Petri dishes containing a pregrown
homokaryon culture. A successful trapping
event was detected by the appearance of
dikaryotic growth (with clamp connections).
Deposition rates of 18 spores m 2 h 1 indicate
that there is ample inoculum to ensure the
colonization of most available substrates as soon
as they are available for decay.
The name Schizophyllum refers to the longitudinally
‘split gills’ which are a xeromorphic
adaptation (Figs. 19.16b and 19.17). In dry
weather the ‘gills’ curve inwards so that the
hymenial surface is protected by a series of
adjoining folds. The curvature is due to the
shrinkage of thinner-walled hyphal layers on
drying. Since the remaining tissue of the gill is
composed of thick-walled clamped hyphae which
do not shrink so readily, inward curvature
follows. Dried basidiocarps can be stored for