III. PHYSICAL AND VEGETATIONAL ASPECTS OF THE SAHARA
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Fig. 15. A mushroom, probably Coprinus arenarius, in an arenaceous zone of
the Ougarta mountains.
2. Affinities
The Saharo-sindian zone, which extends over the central and septentrional Sahara, is linked by biogeographers to the "holarctic floral empire,"
while the Soudan-deccanian region, which corresponds to the meridional
Sahara and the savanna, is linked to the "paleotropical floral empire"
(Monod, 1931, 1957, 1968).
Thus there is a Saharo-sindian element in the Saharan flora near the
north and center, and the Soudano-deccanian element becomes more
and more important further south in the Sahara. However, in addition to
these two elements, there is a penetration of Mediterranean influence in
the septentrional Sahara and in the high mountainous regions, and a penetration of tropical influence in the meridional Sahara.
The Saharo-sindian element is characterized by its homogeneity. It
is clearly predominant in the central Sahara where it is represented by
a subgroup of endemic species which are not present in Asia.
The severity of the Saharan environment permits a high degree of
endemism. At the species level, as many as 25% of the plants are endemic
to the Saharan environment; the number of endemic varieties is even
greater. Many species are of Mediterranean origin, especially in the mountainous regions of the central Sahara. Above 1800 meters there is a steppe,
which is characterized by genera of Mediterranean origin not found else-