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Reproduction and dispersal mechanisms

The only way that a lichen can maintain itself
indefinitely is by vegetative propagation, and this can
be achieved in several ways. In some lichens, such
as Cladoniaspp., the dry lichen thallus is brittle, so
fragments can be broken off and transported to new

sites by wind or by animals. Some other lichens pro-

duce special stalk-like structures termed isidia, which

are brittle, so they might be broken off and dispersed

(Fig. 13.19). Other lichens produce masses of powdery

propagules called soredia. These consist of a few photo-

synthetic cells enveloped in fungal hyphae, and they

are readily dispersed by wind (Fig. 13.19).

272 CHAPTER 13

Fig. 13.18Sites of potential nutrient exchange in lichens of the soil crust community of semiarid desert soils. (a) Three
green algal cells (labeled a) firmly attached to a hypha in the medulla of the lichen Peltula(see Fig. 13.22 for an image
of Peltula). The arrowhead shows a hyphal projection into an algal cell. (b) A cyanobacterial lichen (Collemasp., which
is one of the gelatinous lichens); fungal pegs are closely associated with depressions in the cyanobacterial cells, which
are surrounded by a gelatinous sheath.

(a) (b)

Fig. 13.19Isidia (a) and soredia (b): two methods of vegetative dispersal of lichens.

(a) (b)