IV. DESERT ALGAE, LICHENS, AND FUNGI
187
hydroxide. It appears on a variety of rocks in deserts such as sandstones,
limestones, silicified limestones, etc. (Schefïer et al, 1963; Krumbein,
1969). These authors point out that the chelating activity of the metabolic
products of algae may have a role in the deposition of manganese and
iron.
II. Desert Lichens
A. INTRODUCTION
Lichens can exist under the most stringent conditions in terrestrial desert
regions; their ability to adapt to xeric environments has enabled some types
of lichens to dominate in habitats where competition from other plants
is very slight. In such areas, they may be among the pioneers and at the
same time form the last stage in plant succession. Hale (1967) assumes
that " . . . at some early stage in evolution, both the lichenized fungi and
Trebouxia [which is the most common alga of lichens] may have been
faced with near extinction in competition with nonlichenized fungi and
algae. Through lichenization they have passed from a very precarious existence to their present numerical superiority over other plants in pioneer
habitats."
B. FLORISTIC ACCOUNTS
An early impression that extremely arid desert areas are poor in lichens
(Von Humboldt, 1826; Zukal, 1896) has been refuted by later investigators. Herre (1911), although he believed that desert conditions are in the
main unfavorable to the growth of lichens as evidenced by the limited number of genera and species represented, has nevertheless observed ". . . almost everywhere (in the desert) the rocks are just as thickly covered with
lichens as in other regions of greater humidity and less sunshine. The desert
does not lack in number of individuals, but in number of species of lichens
able to adapt themselves to its conditions."
More recent surveys, however, apparently based on more detailed observations which permitted the identification of barely distinguishable species,
indicate that a relatively great number of genera and species of lichens
exist in desert regions. Follmann (1965a) reported on 153 lichen species
in the Atacama Desert, as compared with 49 phanerogams in the same
area.
Clumps of Teloschistes peruensis (Ach.) Thorns., sometimes intermingled with Anaptychia neoleucomelaena f. squarrosa (Vain.) Kurok.
have been found by Iltis (Thomson and Iltis, 1968) on a small strip of land
in the coastal desert of southern Peru, which is one of the world's most
187
hydroxide. It appears on a variety of rocks in deserts such as sandstones,
limestones, silicified limestones, etc. (Schefïer et al, 1963; Krumbein,
1969). These authors point out that the chelating activity of the metabolic
products of algae may have a role in the deposition of manganese and
iron.
II. Desert Lichens
A. INTRODUCTION
Lichens can exist under the most stringent conditions in terrestrial desert
regions; their ability to adapt to xeric environments has enabled some types
of lichens to dominate in habitats where competition from other plants
is very slight. In such areas, they may be among the pioneers and at the
same time form the last stage in plant succession. Hale (1967) assumes
that " . . . at some early stage in evolution, both the lichenized fungi and
Trebouxia [which is the most common alga of lichens] may have been
faced with near extinction in competition with nonlichenized fungi and
algae. Through lichenization they have passed from a very precarious existence to their present numerical superiority over other plants in pioneer
habitats."
B. FLORISTIC ACCOUNTS
An early impression that extremely arid desert areas are poor in lichens
(Von Humboldt, 1826; Zukal, 1896) has been refuted by later investigators. Herre (1911), although he believed that desert conditions are in the
main unfavorable to the growth of lichens as evidenced by the limited number of genera and species represented, has nevertheless observed ". . . almost everywhere (in the desert) the rocks are just as thickly covered with
lichens as in other regions of greater humidity and less sunshine. The desert
does not lack in number of individuals, but in number of species of lichens
able to adapt themselves to its conditions."
More recent surveys, however, apparently based on more detailed observations which permitted the identification of barely distinguishable species,
indicate that a relatively great number of genera and species of lichens
exist in desert regions. Follmann (1965a) reported on 153 lichen species
in the Atacama Desert, as compared with 49 phanerogams in the same
area.
Clumps of Teloschistes peruensis (Ach.) Thorns., sometimes intermingled with Anaptychia neoleucomelaena f. squarrosa (Vain.) Kurok.
have been found by Iltis (Thomson and Iltis, 1968) on a small strip of land
in the coastal desert of southern Peru, which is one of the world's most