Adil GÜNER, Vehbi ESER - optima

Oral Lectures
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BIOGEOGRAPHICAL LINKS BETWEEN THE IRANO-TURANIAN
AND THE MEDITERRANEAN FLORAS: AN INTRODUCTION
Frédéric MEDAIL
Mediterranean Institute of Ecology and Palaeoecology (IMEP, UMR CNRS-IRD 6116), Aix-Marseille University
(University Paul Cézanne), Europôle méditerranéen de l'Arbois, BP 80, F 13545 Aix-en-Provence cedex 04. France.
f.medail@univ-cezanne.fr
The main environmental characteristics of the Irano-Turanian region are continentality, inducing
extreme changes in temperatures and highly contrasted seasons, and low precipitations. This
region constitutes an outstanding centre of plant diversity and speciation for the whole Holarctis.
It is floristically well differentiated from the adjacent regions by an important contingent of
xerophytes, specialy in Astragalus, Acantholimon, Cousinia, and within the Chenopodiaceae. By
examining the phytochoria of ca. 500 plant species of the deserts and subdeserts of Iran, Léonard
(1989) defined indeed an Irano-Turanian regional centre of endemism. Nevertheless, since the
seminal work of Eig (1931) who clearly defined this region, the biogeographical relationships
between the floras of the Mediterranean and the Irano-Turanian regions were differently
interpreted by phytogeographers. Some authors include some of its parts (eg. central Turkey)
within the Mediterranean region, while others placed the Mauritanian steppes Province of North
Africa within the Irano-Turanian region.
Several examples of intraspecific and intrageneric East-West plant disjunctions have been also
noticed for a long time, notably between steppic areas of central and eastern Spain and those of
eastern Mediterranean or central Asia. Diverse hypothesis have been put forward to explain these
biogeographical patterns, and the presence of steppe plant populations in the western
Mediterranean: (i) these western populations are interpreted as relict populations of a formely
ancient (pre-Pleistocene) and wider distribution range, now restricted to some favourable "steppic
refugia"; (ii) they derive from eastern lineages that migrated in a stepping-stone manner across
land masses and potential land-bridges, notably during the driest episodes of the Messinian
salinity crisis (5.5-5.3 Ma); (iii) these extant populations are the result of some - more or less
recent - colonization events through long distance dispersal; (iv) they are the testimony of early
introductions by man in relation to the westward diffusion of agriculture during the
Neolithisation of Mediterranean Europe, between 8500 and 7200 cal BP. Owing to significant
progresses in plant phylogeny and phylogeographical history, a better understanding of these
disjunctions is now possible, and this presentation examine several insights from some recent
studies.
Keywords: Biogeography, Irano-Turanian region, plant disjunction, phylogeography, steppe
plants.
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