Introduction to Fungi, Third Edition

310 PLECTOMYCETES
of the nest-like arrangement of cleistothecia surrounded
by Hülle cells. This species has been used
widely in genetic studies on sexual and parasexual
recombination (Roper, 1966; Bos & Swart,
1995) and, more recently, for experiments on
morphogenetic aspects (see p. 299) as well as
the biosynthetic pathways of penicillin and
mycotoxins (pp. 302 and 304).
Fig11.17 Emericella nidulans. (a) Conidiophore. Note that the
phialides are not borne directly on the vesicle. (b) Hu«lle cells,
thick-walled cells surrounding the ascocarp. (c) Ascus and
ascospores. Note that the ascospores bear a double flange.
(a) and (c) to same scale.
(Fig. 11.17b). Whereas the ascospores of Eurotium
are colourless and without conspicuous ornamentations,
those of Emericella are red and bear
a prominent double equatorial flange, so that
the spores resemble pulley wheels (Fig. 11.17c).
The conidiophores also differ in that the phialides
are not borne directly on the vesicle but on
a series of cylindrical cells termed metulae.
The best-known species is the soil fungus
Emericella (Aspergillus) nidulans, so called because
11.4.8 Penicillium and its teleomorphic
states
Keys to Penicillium have been provided by Pitt
(1979, 2000) and Ramírez (1982). The anamorphic
genus Penicillium presents the same kind of taxonomic
and nomenclatural problems as Aspergillus.
The classical conidial apparatus is a branched
conidiophore, bearing successive whorls of
branches which terminate in clusters of phialides
(Figs. 11.11, 11.18). Members of the subgenus
Aspergilloides produce phialides directly on
the conidiophore and are thus superficially similar
to Aspergillus. An example is P. spinulosum
(Fig. 11.18a). More commonly, the phialides are
borne on a further whorl of branches, the
metulae, and such species are grouped by their
phialide shape and depending on whether the
penicilli are symmetrical (subgenus Biverticillium)
or more irregular (subgenus Furcatum). Examples
are given in Figs. 11.18b,c. A third possibility
is that the metulae may in turn arise from a
further verticil of branches, the rami (subgenus
Penicillium; e.g. P. expansum, Fig. 11.18d). In some
species, e.g. P. claviforme, the individual conidiophores
may be aggregated together into clubshaped
fructifications or coremia (Fig. 11.19).
As in the case of Aspergillus, the morphology
of the conidiophore unfortunately does not
correlate with DNA sequencing data (Peterson,
2000a), and it is possible that Penicillium will
eventually be broken up into several new genera.
However, whilst of only limited taxonomic value,
the conidiophore architecture will continue
to be used for identification purposes. Some
species of Penicillium have teleomorphs which
can be assigned to Talaromyces or Eupenicillium.
The different kinds of ascocarp represented by
these generic names can be correlated weakly
with conidiophore branching (see below). As for