Introduction to Fungi, Third Edition

LECANORALES
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Fig16.8 Cladonia pyxidata. Primary squamulose thallus
bearing funnel-shaped podetia. Note the granular soredia
outside and inside the podetia.
contain algal cells. The red colour of the
apothecia is due to pigments in the tips of the
paraphyses (Fig. 16.7b).
Fig16.7 Peltigera polydactyla. (a) V.S. thallus. (b) Ascus,
ascospores and paraphyses.
forms of the same lichen are then termed a
morphotype pair or ‘lichen chimera’. The
apothecia of Peltigera are reddish-brown, folded
extensions of the thallus (Plate 8d) which do not
16.3.4 Cladonia
There are about 400 species of Cladonia, some of
them extremely common, growing in heaths,
moors and elsewhere on rocks and walls. There
are two kinds of thallus. The primary thallus is
squamulose, and the secondary thallus is upright
and cylindrical (fruticose), often consisting of a
hollow stalk which bears the apothecium at its
tip. Such an apothecium-bearing vertical thallus
arising from a horizontal primary thallus is
called a podetium and is typical of the genus
Cladonia. InC. pyxidata, the podetium opens out
into a cup (Fig. 16.8), and the apothecia ultimately
develop at the rim of the podetium. In C.
floerkiana (Plate 8e), the podetia are shrub-like
and bear their red apothecia as terminal heads.
The colloquial name for this species is ‘British
soldiers’. The podetia frequently bear the granular
soredia which contain algal cells surrounded
by fungal hyphae (Fig. 16.2). In windtunnel
experiments using C. pyxidata, Brodie and
Gregory (1953) showed that soredia were blown
away from the funnel-shaped podetia at wind
speeds as low as 5.4 7.2 km h 1 although they
were not removed from horizontal glass slides at
the same wind speeds. They suggested that
funnel-shaped structures generate eddy currents