Introduction to Fungi, Third Edition

GASTEROMYCETES IN THE BOLETOID CLADE
587
Fig 20.5 Scleroderma citrinum. (a) Maturing gasterocarps, about 3 6 cm in diameter.One has been cut open to reveal the gleba
containing purplish-black basidiospores. (b) Old gasterocarps.The peridium has cracked open, permitting passive dispersal of the
black basidiospore mass.
In mature gasterocarps, the peridium is
apparently a single, fairly thick layer. Although
the glebal mass may be traversed by a system
of sterile veins, there is no columella and
no capillitium. The basidiospores are sessile
(Fig. 20.6). When the gasterocarp is ripe, it
cracks open irregularly and the dry spores
escape (Fig. 20.5b). There is no well-developed
bellows mechanism as in Lycoperdon (p. 579) or
Geastrum (p. 588).
Fig 20.6 Scleroderma verrucosum. Basidia and basidiospores.
Note that the spores are almost sessile.
S. verrucosum (Pegler et al., 1995). Earth balls are
found in the autumn in acid woodlands and
heaths under such trees as Pinus, Betula, Quercus
and Fagus with which they form ectomycorrhizal
associations. Mycorrhizal infection is easily
reproduced under laboratory conditions, using
aqueous spore suspensions (Parladé et al.,
1996). General aspects of mycorrhiza involving
Scleroderma have been reviewed by Jeffries (1999).
20.4.2 Rhizopogonaceae: beard truffles
This family comprises some 150 species in
4 genera. By far the most important genus is
Rhizopogon, which is mycorrhizal mostly
with coniferous trees. It originates from the
Northern Hemisphere, with an unusually high
diversity of species encountered in the Pacific
Northwest where several host trees are native
(Martín, 1996; Molina et al., 1999). Rhizopogon is
related to Suillus in the boletoid clade (Grubisha
et al., 2001).
Rhizopogon
Members of this genus form gasterocarps which
resemble those of Scleroderma but are hypogeous,
arising from mycelial cords (Plate 11c).
The gasterocarps may be eaten by burrowing