Synopsis of Potamogetonaceae in Iran with supplements to the Flora Iranica and a new identification key Author Abbasi, Shabnam * Department of Biology, Faculty of Science, University of Isfahan, P. O. Box 73441 - 81746, Isfahan, Iran Author Afsharzadeh, Saeed * Department of Biology, Faculty of Science, University of Isfahan, P. O. Box 73441 - 81746, Isfahan, Iran Author Dinarvand, Mehri Forests and Rangelands Research Department, Khuzestan Agricultural and Natural Resources Research and Education Center, Agricultural Research Education and Extension Organization (AREEO), Ahvaz, Iran Author Wiegleb, Gerhard Department of Ecology, BTU Cottbus-Senftenberg, Cottbus, Germany text Phytotaxa 2017 2017-06-23 311 1 1 21 http://dx.doi.org/10.11646/phytotaxa.311.1.1 journal article 10.11646/phytotaxa.311.1.1 1179-3163 13686054 Potamogeton natans Linnaeus (1753:126) , Fig. 9 Perennial, rhizome robust, wintergreen with phyllodial shoots, stem robust, terete, dark-spotted at base. Leaves dimorphic; submersed leaves phyllodial, 100–600 mm long, 0.5–3.5 mm wide, acute at apex, straight at base, 1–3- veined; floating leaves petiolate, oblong-lanceolate to ovate, 50–80 mm long, 50–100 mm wide, acute or obtuse at apex, rounded or subcordate at base, 20-veined, petiole 40–100 mm long, with a flexible discolored joint and a distinct angle at the top; stipules not fused, 5–8 cm long, membranous, persistent. Spike 25–35 mm long, peduncle 70–85 mm long, as thick as stem. Tepals 1–2 mm long, anthers 1 mm long. Carpels 4, fruits 3–4 mm long, indistinctly keeled. Stele of proto type , endodermis of U-type, strong interlacunar bundles present, subepidermal bundles present. FIGURE 9. P . natans a. cross section of stem (Scale bar: 100 μm, objective lens 4), b. morphological shape. World distribution: —W Asia (Afghanistan, Pakistan, Turkey), circumpolar, boreal and temperate regions of the Northern Hemisphere. Distribution in Iran : —North, West. Flowering time: —From spring to summer. Specimen examined :— IRAN . Golestan : Northwest of national park of Golestan , 1349 m , 20August 1999 , Akhani 17050 ( HUT !) ; Lorestan : Gahar lake , 2350 m , 8 Sep 2010 , Dinarvand 20211 ( Herbarium of the Research Center of Agriculture & Natural Resources of Khuzestan !) ; East Azerbaijan : Tikmeh dash, 1900 m , 12 Sep 2013 , Bagheri 20210 ( HUI !) .