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E. IMRE FRIEDMANN AND MARGALITH GALUN
2. Lithophytic (Rock) Algae
Lithophytic (rock) algae live in rocks below the surface. As a rule,
they are either in the fissures (chasmolithic forms), or in the internal air
spaces of the rock fabric (endolithic forms), though intermediary forms
also occur.
a. Chasmolithic Algae. These are known from the deserts of Central
Asia and the Arctic (Odintsova, 1941; Glazovskaya, 1950; Gromov, 1957;
Royzin, 1960), the Negev (Friedmann, 1964; Friedmann et al., 1967), and
the Southwestern United States and Mexico (Friedmann 1972, and unpublished). They occur in a variety of rocks in spaces which range from coarse
cracks to microscopic fissures (Fig. 7). In perpendicular fissures the algae
may appear on the exposed surface of the split as a thin horizontal belt
running a few millimeters under the surface.
In certain other cases, as in heavily weathered and crumbling granites,
the algae grow, in a rather irregular fashion, between disintegrated particles
of the rock. Under weathered and flaking crusts of limestone, dolomite, granite, or quartz, chasmolithic algae may form extended horizontal growths.
It is characteristic of chasmolithic growths that the space occupied by algae
is open onto the rock surface. Thus, especially in coarser fissures, a soillike debris may accumulate and ecological conditions may become somewhat similar to hypolithic habitats. This situation is then reflected in the
composition of the flora as in coarse cracks in limestone rocks of the Negev
Desert. In these localities the flora is similar to hypolithic habitats, while
in weathered granites (Western Pamir, Israel, and North American
deserts) it is formed by species of Gloeocapsa.
b. Endolithic Algae. In contrast to chasmolithophytes, endolithic algae
occupy a space in the rock fabric with no apparent connection to the outer
rock surface; they have been found in the Negev Desert of Israel and in
Death Valley in sandstone, crystalline limestone (Fig. 8) and amorphous
limestone (Fig. 9) rocks (Friedmann, 1964; Friedmann et al., 1967;
Friedmann, 1971). The rocks colonized by endolithic algae, though both
chemically and petrologically of different types, share certain common
characteristics: They are light colored and their physical structure is
porous and sponge-like. The algae occupy a horizontally extended zone
in the rock and colonize the spaces between the particles. As a rule, the
algal zone runs under the surface in a remarkably uniform depth and follows its contours.
Above the algal zone, the spaces between the particles of the porous
rock are filled with mineral substance. This results in a dense surface crust
which seals the internal air space system from the outside environment.
The crust is normally about 0.1-3.0 mm thick and the algal zone itself
E. IMRE FRIEDMANN AND MARGALITH GALUN
2. Lithophytic (Rock) Algae
Lithophytic (rock) algae live in rocks below the surface. As a rule,
they are either in the fissures (chasmolithic forms), or in the internal air
spaces of the rock fabric (endolithic forms), though intermediary forms
also occur.
a. Chasmolithic Algae. These are known from the deserts of Central
Asia and the Arctic (Odintsova, 1941; Glazovskaya, 1950; Gromov, 1957;
Royzin, 1960), the Negev (Friedmann, 1964; Friedmann et al., 1967), and
the Southwestern United States and Mexico (Friedmann 1972, and unpublished). They occur in a variety of rocks in spaces which range from coarse
cracks to microscopic fissures (Fig. 7). In perpendicular fissures the algae
may appear on the exposed surface of the split as a thin horizontal belt
running a few millimeters under the surface.
In certain other cases, as in heavily weathered and crumbling granites,
the algae grow, in a rather irregular fashion, between disintegrated particles
of the rock. Under weathered and flaking crusts of limestone, dolomite, granite, or quartz, chasmolithic algae may form extended horizontal growths.
It is characteristic of chasmolithic growths that the space occupied by algae
is open onto the rock surface. Thus, especially in coarser fissures, a soillike debris may accumulate and ecological conditions may become somewhat similar to hypolithic habitats. This situation is then reflected in the
composition of the flora as in coarse cracks in limestone rocks of the Negev
Desert. In these localities the flora is similar to hypolithic habitats, while
in weathered granites (Western Pamir, Israel, and North American
deserts) it is formed by species of Gloeocapsa.
b. Endolithic Algae. In contrast to chasmolithophytes, endolithic algae
occupy a space in the rock fabric with no apparent connection to the outer
rock surface; they have been found in the Negev Desert of Israel and in
Death Valley in sandstone, crystalline limestone (Fig. 8) and amorphous
limestone (Fig. 9) rocks (Friedmann, 1964; Friedmann et al., 1967;
Friedmann, 1971). The rocks colonized by endolithic algae, though both
chemically and petrologically of different types, share certain common
characteristics: They are light colored and their physical structure is
porous and sponge-like. The algae occupy a horizontally extended zone
in the rock and colonize the spaces between the particles. As a rule, the
algal zone runs under the surface in a remarkably uniform depth and follows its contours.
Above the algal zone, the spaces between the particles of the porous
rock are filled with mineral substance. This results in a dense surface crust
which seals the internal air space system from the outside environment.
The crust is normally about 0.1-3.0 mm thick and the algal zone itself