Introduction to Fungi, Third Edition

604 HETEROBASIDIOMYCETES
the hymenium may germinate by repetition or,
in other situations, by means of a germ tube, but
lunate or other microconidia have not been
observed (Ingold, 1985).
21.5 Tremellales
Fig 21.8 Exidiaglandulosa.Sectionofhymeniumshowing
longitudinally divided basidia with long epibasidia extending to
the surface.
Formerly understood as a broad taxon which
included genera such as Exidia and Pseudohydnum
(see p. 603), the order Tremellales is now
restricted to fungi which possess a yeast-like
haploid state, basidia divided by longitudinal
septa (tremelloid basidia), and dikaryotic hyphae
with a dolipore septum and a parenthesome
which is sacculate, i.e. invaginated towards the
septal pore (Fig. 21.10a; Berbee & Wells, 1988).
Dikaryotic hyphae usually have clamp connections.
The monokaryotic yeast state resembles
heterobasidiomycete yeasts such as Filobasidiella
neoformans, Phaffia rhodozyma and species of
Bullera and Cryptococcus, all of which belong to
the Tremellales and related orders within the
Tremellomycetidae (Fell et al., 2001). Heterobasidiomycetes
growing predominantly in the
yeast state are discussed in Chapter 24 (p. 660).
In the life cycle of the filamentous Tremellales
considered here, the dikaryotic condition is the
dominant phase and is re-established by
Fig 21.9 Fruit bodies of Auriculariales. (a) Exidiaglandulosa.Fruit bodies on lime (Tilia).The hymenial surface bears black warts and
is on one face of the fruit body. (b) Pseudohydnum gelatinosum.Fruit bodies seen from above (right) and below (left).The hymenium
covers the surface of the spines.