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Universität Bayreuth (2017)

Diversity of the genus Euphorbia (Euphorbiaceae) in SW Asia.

Pahlevani, Amir Hossein

Titre : Diversity of the genus Euphorbia (Euphorbiaceae) in SW Asia.

Auteur : Pahlevani, Amir Hossein

Université de soutenance : Universität Bayreuth

Grade : Doctoral thesis, 2017

Résumé
Euphorbia is one of the three most species-rich genera of flowering plants with more than 2000 species occurring in all temperate and tropical regions. They occupy a wide range of habitats and exhibit great diversity in growth forms. In habit, the species vary from small ephemerals to various forms of herbaceous annuals or perennials, cushion-forming subshrubs, large shrubs, small trees and cactus-like succulents. After recent molecular studies, Euphorbia has been divided into four monophyletic subgenera including, Athymalus (c. 150 species), Chamaesyce (c. 600 species), Esula (c. 500 species) and Euphorbia (c. 800 species). Taxonomy of Euphorbia is extremely difficult due to the species richness accompanied by a cosmopolitan distribution, the extreme morphological plasticity among certain species and convergent evolution of certain morphological characters. As a consequence, the circumscription of the Euphorbia species especially in SW Asia remained unresolved. To resolve phylogenetic and taxonomic complex groups and uncertainties among the species of the genus Euphorbia, this thesis aims 1) to complete phylogenetic and phylogeographic study of the genus (subgen. Esula) in SW Asia, by integrating hitherto unanalyzed species in the existing phylogeny using the markers ITS and ndhF, 2) to study seed and capsule morphology of the Iranian species of Euphorbia and study their evolution by plotting them on the molecular phylogenetic tree, 3) to evaluate the genotypic diversity of some complex, rare or endemic Iranian Euphorbia species (section Esula) using ISSR DNA fingerprinting, 4) to trace diversification, endemism, distribution and conservation status of the genus Euphorbia in SW Asia, 5) to update the taxonomic treatment of the two largest sections, Helioscopia and Esula of the subgenus Esula in Iran. The phylogenetic relationships of Iranian species based on internal transcribed spacer (ITS) nuclear and ndhF plastid regions are updated and used for the characterization of the synapomorphies of each clade in subgenus Esula. It is confirmed that there are 13 sections in subgenus Esula in Iran. The presence or absence of granulate elements on seed surfaces represents a phylogenetically important trait for section delimitation. The capsule surface is synapomorphic for several sections, including Helioscopia (tuberculate-verrucose), Myrsiniteae (vesiculate) and Esula (granulate) and seed shape is synapomorphic for sections Helioscopia (ellipsoidal), Myrsiniteae (ovoid-quadrangular) and Herpetorrhizae (pseudo-hexahedral). However, reversals have also taken place in some features, including capsule surface (E. mazandaranica, E. altissima) and seed shape (E. densa, E. aleppica). Evaluation of diversity, endemism, distribution and conservation status of the genus Euphorbia is based on the study of specimens in herbaria rich in SW Asian material and benefits from field excursions in Iran. A total of 22,000 specimens from 20 countries (Afghanistan, Armenia, Azerbaijan, Cyprus, Egypt, Iran, Iraq, Israel/Palestine, Jordan, Kuwait, Lebanon, Oman, Pakistan, Qatar, Saudi Arabia, Syria, Turkey, Turkmenistan, UAE, Yemen) have been studied, including almost all type specimens reported from the studied region. Genus Euphorbia in SW Asia (area of study) has 249 taxa of all four existing subgenera comprising, Athymalus (13 taxa), Chamaesyce (33 taxa), Esula (182 taxa) and Euphorbia (21 taxa) with three, six, 19 and two sections respectively. Among 20 studied countries in the region, Turkey, Iran and Syria with 103, 90 and 50 species are the richest countries, respectively. The highest number of endemics occurs in Iran, Turkey and Yemen with 19, 13 and eight taxa respectively. Analysis of diversity indicated that the richest places of Euphorbia in the extended SW Asia were eastern part of the Mediterranean region (<32 taxa), Alborz, Zagros (Iran) and Anti-Taurus (S Turkey) (<25 taxa) mountains are the second richest areas followed by SW and W Yemen, Lesser Caucasus, N Turkey and west Himalaya (c. 20 taxa). 96 endemic taxa in the region were evaluated against the IUCN Red List categories and criteria and a total of 54 endemic taxa were globally classified as threatened comprising 21 Critically Endangered, 16 Endangered and 17 Vulnerable taxa. Based on morphological and molecular works, nine species new to science, 15 new records for several countries in the studied region and six synonyms are recognized. Two largest sections Esula and Helioscopia have been revised in Iran. Description, typification, synonyms, data on distribution and habitat, key to species and pertinent comments are given.

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