Mitteilungen des Kärntner Botanikzentrums Klagenfurt 98 Wulfenia 23 (2016): 98 –112 Species delimitation and population structure analysis in Polygonum species (section Polygonum) Samaneh Mosaferi, Masoud Sheidai, Maryam Keshavarzi & Zahra Noormohammadi Summary: The genus Polygonum L. (Polygonaceae) contains about 230 species that are distributed worldwide. These herbaceous annuals and shrubby perennials are usually invasive in nature and occupy diferent geographical regions. They show morphological and genetic plasticity and they are diicult to deal with taxonomically. In spite of many Polygonum species that grow in Iran, we do not have any report on their population genetic structure, mode of divergence and dispersal. Therefore, we planned molecular (ISSR markers) and morphological studies of 37 accessions from 17 species of Polygonum (section Polygonum) that were collected from diferent regions in Iran. We try to address the following questions: 1) can ISSR markers delimit Polygonum species, 2) what is the genetic structure of these taxa in Iran, and 3) what evolutionary forces are acting for Polygonum species divergence? MDS plot of morphological characters separated annual species from perennials. ISSR molecular markers revealed a low degree of genetic variability in some of the studied species but showed high genetic diversity in some others. AMOVA showed strong genetic diferentiation among the studied species. STRUCTURE analysis and assignment test revealed some degree of genetic admixture among studied species / populations. The present study show that invasion followed by genetic divergence due to genetic drift and inbreeding, local adaptation and occasional interspeciic cross-pollination are the major evolutionary forces in Polygonum species and populations divergence. Keywords: Polygonum, ISSR, genetic divergence, morphological variability Polygonum L. with about 230 species in the world is the largest genus of Polygonaceae (Galasso et al. 2009; Voylokova et al. 2009). The genus as a whole has a wide distribution ranging from the tropics to the polar region and from sea level to the highest altitudes. There has always been disagreement on classiication of Polygonum s.l. and diferent subdivisions on section and genus level have been reported (Meissner 1826; Bentham & Hooker 1880; Gross 1913; Hedberg 1946; Haraldson 1978; Ronse Decraene & Akeroyd 1988). According to Lamb-Frye & Kron (2003), molecular analysis on Polygonum species of North America showed that Polygonum is paraphyletic. Phylogenetic studies on European Polygonum conirm that Polygonaceae are monophyletic and the subfamily Polygonoideae seems to be paraphyletic (Galasso et al. 2009). In this study, Polygonum s.str. (tribe Polygoneae) has been adopted. According to previous studies, 29 taxa of Polygonum s.str. belonging to 4 sections (Tiniaria Meisn., Aconogonon Meisn., Pleuropterus (Turcz.) Bentham & Hooker., Polygonum Tourn.) occur in Iran (Rechinger & Schiman-Czeika 1968; Mozaffarian 2012). Polygonum s.str. species are annual and perennial herbs, subshrubs or shrubs with woody stocks (Li et al. 2003). Their stems are erect, prostrate or ascending, usually with conspicuously swollen nodes. All of them have membranous tubular ochreas. Their leaves are linear, lanceolate, elliptic, ovate or oblong with or without petioles. Inlorescences are axillary with solitary lowers or few lowered fascicles or lax spikes. Some of them are weeds, while some others have ornamental and medicinal importance across the world (Rechinger & Schiman-Czeika 1968; Qaiser 2001).