Introduction to Fungi, Third Edition

588 HOMOBASIDIOMYCETES: GASTEROMYCETES
mammals, and basidiospores pass through their
digestive tracts unharmed (Colgan & Claridge,
2002). Rhizopogon luteolus and R. roseolus are
common and cosmopolitan under Pinus spp.,
whereas R. vinicolor and others are specific
associates of Douglas fir (Pseudotsuga menziesii).
Reviews of the genus have been written
by Molina and Trappe (1994) and Molina
et al. (1999).
Rhizopogon spp. provide similar benefits to
their hosts as Pisolithus and are the subject of
research and development activities in forestry.
Inoculation is readily achieved by dusting seeds
with basidiospores or immersing the roots of
seedlings in spore suspensions (Parladé et al.,
1996). Although Rhizopogon spp. can be grown in
pure culture, inoculation of host tree seedlings
with mycelium is not generally efficient with
this and related fungi, unless the hyphae are
protected from mechanical damage, for example,
by being grown inside porous or gel-like beads
(see Smith & Read, 1997).
20.5 Gasteromycetes in the
gomphoid phalloid clade
The gomphoid phalloid clade contains some
350 species of morphologically diverse fungi
(Hibbett & Thorn, 2001). Most of the species
with active basidiospore discharge form coral- or
club-shaped basidiocarps, e.g. Ramaria (see Plate
10h), Clavariadelphus and Gomphus. Several groups
of well-known gasteromycetes also belong here
(Hibbett et al., 1997b; Humpert et al., 2001), and
these show the most spectacular spore dispersal
mechanisms of all gasteromycetes, including
the bellows mechanism, insect dispersal, and
active discharge of peridioles. Details of the
phylogeny or evolutionary history of these
gasteromycetes still appear to be unknown,
although some groups such as earth stars may
be ancient (Krassilov & Makulbekov, 2003).
Members of the gomphoid phalloid clade are
mostly saprotrophic on wood, other plant debris
and humus, extending to the soil by means of
mycelial cords.
20.5.1 Geastraceae: earth stars
There are some 50 species of earth stars.
Descriptions of the common species may be
found in the keys by Ellis and Ellis (1990) and
Pegler et al. (1995). One of the most frequent and
widespread species in temperate and subtropical
forests is Geastrum triplex (Fig. 20.7a) which grows
in the leaf litter of beech, sycamore and pine. The
young fruit body is onion-shaped and develops at
or just below the soil surface. The exoperidium is
complex, consisting of a brown outer layer made
of narrow hyphae mostly running longitudinally,
and a paler pseudoparenchymatous inner
layer. As the fruit body ripens, the whole of the
exoperidium splits open from the tip in a stellate
fashion and, due to swelling of the pseudoparenchyma
cells of the exoperidium, the triangular
flaps curve outwards and make contact with the
soil, lifting the inner part of the fruit body into
the air (Fig. 20.7a). The thin, papery endoperidium
opens by an apical pore. Spores are puffed
out by the bellows mechanism when rain drops
strike the endoperidium (Ingold, 1971). The
gleba contains a columella (sometimes termed
a pseudocolumella) and capillitium, much as in
the puffball Lycoperdon (Fig. 20.3) with which
Geastrum is not related. Basidial development can
only be observed in young unexpanded gasterocarps.
The basidia are pear-shaped, with 4 6
(sometimes up to 8) spores borne on a knob-like
extension of the pointed end.
20.5.2 Sphaerobolus
Sphaerobolus is unique among gasteromycetes in
that it has developed an active discharge
mechanism of peridioles (glebal masses), thereby
reversing the loss of active basidiospore liberation.
The precise taxonomic position of
Sphaerobolus is still unclear at present; formerly
grouped together with the bird’s nest fungi
(p. 578), it is now known to belong to the
gomphoid phalloid clade. Kirk et al. (2001) have
included it in the Geastraceae.
Sphaerobolus stellatus forms globose orange
gasterocarps about 2 mm in diameter. They are
attached to rotten wood, rotting herbaceous
stems, sacking and weathered dung of herbivores
such as cow and sheep. Ripe fruit bodies open