IV. DESERT ALGAE, LICHENS, AND FUNGI
177
rainwater penetrates along the stone-soil interphase more deeply than at
other places and that a small water reservoir persists under the stone after
the water has evaporated from the surrounding area.
In the South African desert, a remarkable ecological convergence exists
between algae, higher plants and lichens. Certain higher plants—succulent Aizoaceae and Liliaceae appropriately called in German Fensterpfianzen—are reduced to a few cylindrical, truncate, fleshy leaves, which
are buried in the soil with their flattened upper side at surface level.
Through this "window" light penetrates the colorless, fleshy parenchymatous
tissue of the plant where it is scattered and partly absorbed. The assimilating
cells line the inner surface of the fleshy tissue. This tissue functionally corresponds to the translucent stone, and the position of the chlorophyllcarrying cells is similar to that of the algal growth under the stone.
In lichens (Lecidea, Toninia, Endocarpon, Eremastrella) which also
grow buried in the soil with their upper side at surface level, the translucent, colorless, light-absorbing substance is represented by a mass of fungal
hyphae. The position of the phycobionts corresponds to the photosynthesizing tissue in the higher window plants or to the hypolithic algal layer
under the quartz stones.
The flora of hypolithic habitats is usually varied and comprises filamentous and coccoid blue-green and green algae. In the Negev Desert,
Friedmann et al. (1967) and R. Ocampo (unpublished) found the
following species: green algae—Bracteacoccus sp., Chlorosarcinopsis
negevensis Friedmann et Ocampo-Paus, Chlorosarcinopsis sp., Friedmannia israeliensis Chatanachat et Bold, Hormidium sterile Deason et Bold,
Hormidium subtilissimum (Rabenh.) Mattox et Bold, Radiosphaera
negev ensis Ocampo-Paus et Friedmann, Stichococcus sp., Trebouxia sp.,
(probably lichen phycobiont), Trochiscia sp., and Ulothrix minuta Mattox
et Bold; blue-green algae—Paracapsa sp., (perhaps a growth form of Gloeocapsa) seems to be the most characteristic organism on flint stones, also
Aphanocapsa sp., Aphanothece sp., Gloeocapsa spp., Lyngbya spp., Microcoleus chtonoplastes Thur., Myxosarcina sp., Nostoc spp., Plectonoma
sp., Schizothrix calcicola (Ag.) Gom., Schizothrix spp., Scytonema sp.,
and Tolypothrix byssoidea (Berkeley) Kirchner. Scytonema ocellatum
Lyngbye is reported from Heliopolis, Egypt. Durrell (1962) lists from
Death Valley Tolypothrix distorta Kiitz., Nostoc muscorum Ag., Microcoleus vaginatus (Vauch.) Gom., Anacystis montana (Lightf.) Drouet et
Daily, Phormidium tenue (Menegh.) Gom., Phormidium retzii (Ag.)
Kiitz., Phormidium subcapitatum Boye Peters, and Chorella vulgaris Beij.
Phormidium tenue (Menegh.) Gom., which occurs under crusts of salt in
Death Valley, perhaps represents a peculiar form of hypolithic growth.
177
rainwater penetrates along the stone-soil interphase more deeply than at
other places and that a small water reservoir persists under the stone after
the water has evaporated from the surrounding area.
In the South African desert, a remarkable ecological convergence exists
between algae, higher plants and lichens. Certain higher plants—succulent Aizoaceae and Liliaceae appropriately called in German Fensterpfianzen—are reduced to a few cylindrical, truncate, fleshy leaves, which
are buried in the soil with their flattened upper side at surface level.
Through this "window" light penetrates the colorless, fleshy parenchymatous
tissue of the plant where it is scattered and partly absorbed. The assimilating
cells line the inner surface of the fleshy tissue. This tissue functionally corresponds to the translucent stone, and the position of the chlorophyllcarrying cells is similar to that of the algal growth under the stone.
In lichens (Lecidea, Toninia, Endocarpon, Eremastrella) which also
grow buried in the soil with their upper side at surface level, the translucent, colorless, light-absorbing substance is represented by a mass of fungal
hyphae. The position of the phycobionts corresponds to the photosynthesizing tissue in the higher window plants or to the hypolithic algal layer
under the quartz stones.
The flora of hypolithic habitats is usually varied and comprises filamentous and coccoid blue-green and green algae. In the Negev Desert,
Friedmann et al. (1967) and R. Ocampo (unpublished) found the
following species: green algae—Bracteacoccus sp., Chlorosarcinopsis
negevensis Friedmann et Ocampo-Paus, Chlorosarcinopsis sp., Friedmannia israeliensis Chatanachat et Bold, Hormidium sterile Deason et Bold,
Hormidium subtilissimum (Rabenh.) Mattox et Bold, Radiosphaera
negev ensis Ocampo-Paus et Friedmann, Stichococcus sp., Trebouxia sp.,
(probably lichen phycobiont), Trochiscia sp., and Ulothrix minuta Mattox
et Bold; blue-green algae—Paracapsa sp., (perhaps a growth form of Gloeocapsa) seems to be the most characteristic organism on flint stones, also
Aphanocapsa sp., Aphanothece sp., Gloeocapsa spp., Lyngbya spp., Microcoleus chtonoplastes Thur., Myxosarcina sp., Nostoc spp., Plectonoma
sp., Schizothrix calcicola (Ag.) Gom., Schizothrix spp., Scytonema sp.,
and Tolypothrix byssoidea (Berkeley) Kirchner. Scytonema ocellatum
Lyngbye is reported from Heliopolis, Egypt. Durrell (1962) lists from
Death Valley Tolypothrix distorta Kiitz., Nostoc muscorum Ag., Microcoleus vaginatus (Vauch.) Gom., Anacystis montana (Lightf.) Drouet et
Daily, Phormidium tenue (Menegh.) Gom., Phormidium retzii (Ag.)
Kiitz., Phormidium subcapitatum Boye Peters, and Chorella vulgaris Beij.
Phormidium tenue (Menegh.) Gom., which occurs under crusts of salt in
Death Valley, perhaps represents a peculiar form of hypolithic growth.