Introduction to Fungi, Third Edition

546 HOMOBASIDIOMYCETES
in a sinuous or labyrinth-like pattern in contrast
with the regular folding seen in the mature
stage. During the elongation stage, expansion of
the stipe and cap causes the universal veil to
rupture. In addition to the primary gills which
run along the entire radius of the cap, secondary
or tertiary gills, extending for shorter distances,
develop either by successive bifurcation of an
older gill near its inner, free edge or by the
formation of a new hymenial layer at or near the
root of an old gill. The hymenium includes
basidia and larger, skittle-shaped facial cystidia
which may extend across to the opposite gill
face. Droplets observed on the cystidia suggest
that the cystidia may have a secretory role.
Volvariella surrecta is mycoparasitic. Its
basidiocarps grow on the caps of other agarics
such as Clitocybe nebularis (Fig. 19.16d).
19.4.7 Bolbitiaceae
Panaeolus (25 spp.)
Most members are coprophilous but some grow
in pastures. Common examples are P. semi-ovatus
(sometimes classified in a separate genus
Anellaria) and P. sphinctrinus (Fig. 19.16e). Both
species fruit on cattle dung. The gills are
wedge-shaped in section and aequi-hymeniiferous.
The spores are black. Panaeolus spp. are
commonly called mottle-gills, and this refers to
the fact that the basidia ripen in patches, not
uniformly, so that areas in which the spores
are ripe appear darker than those in which
the spores are still immature (Buller, 1922).
Basidiocarps of some Panaeolus spp. contain
psilocybin and are hallucinogenic (see p. 553).
19.4.8 Hygrophoraceae
Members of the Hygrophoraceae are sometimes
included in Tricholomataceae but have been
resolved in recent phylogenetic studies as a
separate family (Moncalvo et al., 2002).
Representative genera are Hygrophorus (100 spp.)
and Hygrocybe (150 spp.), also known as waxcaps
because of the texture of their basidiocarps.
Some species grow in woodland and may form
ectomycorrhiza with trees, e.g. Hygrophorus
eburneus from beech woods (Fagus sylvatica).
However, the characteristic habitats of many
waxcaps are impoverished, non-fertilized
pastures. Their basidiocarps are often slimy or
gelatinous and brightly coloured, e.g. the bloodred
Hygrocybe coccinea (scarlet waxcap; Plate 9c) or
the greenish-yellow Hygrocybe psittacina (parrot
waxcap). The basidiocarps of Hygrocybe conica
(blackening waxcap) turn black when bruised.
19.4.9 Marasmiaceae
Although the Marasmiaceae, like most families
in the euagarics clade, may well become substantially
rearranged in the future, the work by
Moncalvo et al. (2000) lends some support for
the grouping together of key genera such as
Lentinula, Omphalotus, Marasmius, Crinipellis,
Flammulina and Strobilurus. Most fungi formerly
known as Collybia are now also accommodated
in the Marasmiaceae, assigned to the genera
Gymnopus and Rhodocollybia. Several members
of the Marasmiaceae are known to produce
antifungal substances in pure culture, and one
group, the strobilurins, has been developed into
fungicides currently enjoying worldwide application
(Sauter et al., 1999; see p. 410). Some
strobilurins and the related oudemansins have
been shown to be secreted by their producers
into colonized wood at concentrations which are
toxic to potential competitors, thereby indicating
their ecophysiological function as a means of
resource capture and defence (Engler et al., 1998).
Whereas most members of the Marasmiaceae are
saprotrophs on wood and humus, some are
necrotrophic or, rarely, biotrophic pathogens of
trees.
Marasmius (500 spp.)
Species of Marasmius often have rather tough,
leathery basidiocarps which shrivel on drying
but rapidly revive on wetting. The best known
species is M. oreades, the fairy ring fungus whose
basidiocarps are edible and may be dried
(Fig. 19.18a). The mycelium of the fungus
grows outwards from a central point and, as
the mycelial front progresses radially, the
older, trailing mycelium dies. This results in a
ring of active mycelium, visible as a circle of
green grass in lawns and pastures (Fig. 19.18b).
Measurements of the radial extension of growing