Introduction to Fungi, Third Edition

GASTEROMYCETES IN THE BOLETOID CLADE
585
purse. The funicular cord, spirally coiled up
within the purse, swells explosively, stretching to
a length of about 2 3mm in C. stercoreus, whilst
in C. striatus it may be as long as 4 12 cm. As the
peridiole is flicked away, the sticky hapteron
at the base of the funicular cord helps to
attach the peridiole to surrounding vegetation,
and the momentum of the peridiole may cause
the funicular cord to wrap around objects.
Peridioles of C. stercoreus are presumably eaten
by herbivorous animals and it is known that the
basidiospores on release from the peridiole are
stimulated to germinate by incubation around
37°C. Whether animals play a significant role
in the dispersal of other bird’s nest fungi is
uncertain. The funiculus of Crucibulum is different
from that of Cyathus, with a longer middle
piece, a very short purse, and a funicular cord
which is composed of relatively few hyphae only
slightly coiled.
Both Cyathus and Crucibulum show tetrapolar
heterothallism with relatively few alleles
(generally not more than 15) at each locus, and
this is the most usual condition within the
Nidulariaceae (Burnett & Boulter, 1963; Lu, 1964).
20.4 Gasteromycetes in the
boletoid clade
The boletoid clade, as defined by molecular
phylogeny (Hibbett & Thorn, 2001), contains
fungi with a wide range of fruit body types,
including lamellate (e.g. Paxillus), boletoid
(e.g. Boletus, Leccinum, Suillus, Xerocomus) and
resupinate forms (e.g. Coniophora, Serpula). These
have been described previously (Section 19.5).
Gasteromycete fungi have arisen from boletoid
ancestors on several occasions, with the family
Sclerodermataceae having an affinity with
Gyroporus in a ‘boletoid’ branch, and the
Rhizopogonaceae with Suillus (‘suilloid’ branch;
Grubisha et al., 2001; Binder & Bresinsky, 2002).
Both families contain mainly ectomycorrhizal
fungi (see Table 20.1).
Features of their association with tree roots
are typical of members of the boletoid clade in
that there is a large amount of fungal biomass
extending from the mantle into the soil by
means of mycelial cords or rhizomorphs which
may be several metres long. This type of
ectomycorrhiza appears to be particularly effective
in exploiting a large volume of soil for
nutrients, and it is also credited with improving
the water status and thus the performance of the
tree host under conditions of drought (Smith &
Read, 1997; Agerer, 2001). The ability to form an
extensive rhizomorph system may explain why
mycorrhizal gasteromycetes belonging to the
boletoid clade are particularly prominent in dry
habitats. It is probable that long-distance transport
processes in rhizomorphs are facilitated by
peristaltic movement through a system of tubular
vacuoles (Fig. 1.9; Ashford & Allaway,
2002). Certain ectomycorrhizal fungi such as
Rhizopogon, Scleroderma and Pisolithus can be
grown in pure culture, and basidiospore inoculum
from their relatively large fruit bodies is also
easily collected and stored. Hence, these species
are suitable for laboratory-based research as well
as inoculation of trees prior to outplanting into
forestry situations.
In addition to the morphology of ectomycorrhiza,
there are several further features betraying
an affinity of the Sclerodermataceae and
Rhizopogonaceae with the boletoid clade. For
instance, pulvinic acid-type pigments typical of
Boletus, Suillus and Xerocomus (see Fig. 19.22) are
also found in their gasteromycete relatives,
either in a pure form (e.g. variegatic acid,
xerocomic acid) or as derivatives (Gill &
Watling, 1986; Gill & Steglich, 1987; Winner
et al., 2004). Further, the mycoparasitic mould
Apiocrea chrysosperma (anamorph Sepedonium
chrysospermum), which frequently forms a
golden yellow conidial crust on fruit bodies of
Boletus, Suillus, Xerocomus and Paxillus (Plate 9h),
also infects gasteromycetes such as Scleroderma
and Rhizopogon (see Gill & Watling, 1986).
Pathogens may be competent taxonomists!
20.4.1 Sclerodermataceae: earth balls and
relatives
This family comprises some 50 species in
7 genera (Kirk et al., 2001), including the earth
ball Scleroderma, the stalked puffball Calostoma,