III. PHYSICAL AND VEGETATIONAL ASPECTS OF THE SAHARA
153
the occidental Sahara are characterized by the presence of succulent Salsolaceae or Zygophyllacea, in particular, by a steppe of Zygophyllum.
The halophilic vegetation is rare in the central Sahara and the
meridional Sahara where the rigorous climate excludes all vegetable life
on the salty or gypseous surface.
The halophilic and halogypsophilic groups are especially localized in
the northern and occidental regions of the Sahara. They are strangely influenced by Mediterranean progeny. The hyperhalophilic groups are even
considered veritable infiltrations from the Mediterranean region.
4. Groups of Climatic Origin
It is necessary to characterize the large phytogeographic sectors of the
Sahara for these groups.
a. The Oceanic and Western Sahara. ( 1 ) The oceanic Sahara is characterized by an original, not very Saharan, vegetation because of the humidity
and the high altitude there. The vegetation is constituted especially by
a steppe of mixed shrubs and succulent plants; among them the genus
Euphorbia is well represented. The Mediterranean infiltrations are again
numerous in the sector. Nevertheless, one must note a large number of
Macronesian species and a high degree of endemism (Murat, 1944;^
Monod, 1938, 1952; Sauvage, 1946; Hernando-Pacheco et al, 1949). (2)
The western Sahara has a very heterogenous flora, essentially composed of
elements from the Saharan zones which border it. The desert savannah frequently has Acacia-Panicum. Not many studies of the flora have been
carried out (Maire, 1938; Sauvage, 1949; Quézel and Simonneau, 1960).
b. The Northern Sahara. The northern Sahara is characterized by a relatively dense vegetation where annual plants are well represented whereas
trees are absent.
From a biogeographic viewpoint, the Sahara-sindian lines dominate,
but the influence of the mediterranean world is very important. On the
other hand, the tropical lines are absent. Outside of the halophilic and
psammophilic groups, the individualized associations are related to the
saxicole group. The northern Sahara can be divided into two parts:
(1) The northeastern Sahara: The northern region is characterized by
two groups of rockwork and hamada in the northern portion of Mzab (the
association of Moricandia arvensis sp. spinosa-Cymbopogon
schoenanthus
and the association of Anthyllis sericea var. hennonia-Fagonia microphylla
var. fruticans), and by two groups of special vegetation of the south-constantinous Sahara: one is tied to the regs of encrusted gypsum, the association of Stephanochilus omphalodes-Arthrophytum
schmittianum; the
other to lime sands, the association of Brocchia cinerea and Heliotropium
bacciferum. The meridional region is only represented by very diffuse
153
the occidental Sahara are characterized by the presence of succulent Salsolaceae or Zygophyllacea, in particular, by a steppe of Zygophyllum.
The halophilic vegetation is rare in the central Sahara and the
meridional Sahara where the rigorous climate excludes all vegetable life
on the salty or gypseous surface.
The halophilic and halogypsophilic groups are especially localized in
the northern and occidental regions of the Sahara. They are strangely influenced by Mediterranean progeny. The hyperhalophilic groups are even
considered veritable infiltrations from the Mediterranean region.
4. Groups of Climatic Origin
It is necessary to characterize the large phytogeographic sectors of the
Sahara for these groups.
a. The Oceanic and Western Sahara. ( 1 ) The oceanic Sahara is characterized by an original, not very Saharan, vegetation because of the humidity
and the high altitude there. The vegetation is constituted especially by
a steppe of mixed shrubs and succulent plants; among them the genus
Euphorbia is well represented. The Mediterranean infiltrations are again
numerous in the sector. Nevertheless, one must note a large number of
Macronesian species and a high degree of endemism (Murat, 1944;^
Monod, 1938, 1952; Sauvage, 1946; Hernando-Pacheco et al, 1949). (2)
The western Sahara has a very heterogenous flora, essentially composed of
elements from the Saharan zones which border it. The desert savannah frequently has Acacia-Panicum. Not many studies of the flora have been
carried out (Maire, 1938; Sauvage, 1949; Quézel and Simonneau, 1960).
b. The Northern Sahara. The northern Sahara is characterized by a relatively dense vegetation where annual plants are well represented whereas
trees are absent.
From a biogeographic viewpoint, the Sahara-sindian lines dominate,
but the influence of the mediterranean world is very important. On the
other hand, the tropical lines are absent. Outside of the halophilic and
psammophilic groups, the individualized associations are related to the
saxicole group. The northern Sahara can be divided into two parts:
(1) The northeastern Sahara: The northern region is characterized by
two groups of rockwork and hamada in the northern portion of Mzab (the
association of Moricandia arvensis sp. spinosa-Cymbopogon
schoenanthus
and the association of Anthyllis sericea var. hennonia-Fagonia microphylla
var. fruticans), and by two groups of special vegetation of the south-constantinous Sahara: one is tied to the regs of encrusted gypsum, the association of Stephanochilus omphalodes-Arthrophytum
schmittianum; the
other to lime sands, the association of Brocchia cinerea and Heliotropium
bacciferum. The meridional region is only represented by very diffuse