Description Potamogeton perfoliatus

perfoliate pondweed growing in canal. note leaves clasping stem.

perfoliate pondweed grows robust creeping perennial rhizome, intermittently producing round stems 3 m long. submerged leaves oval , translucent, no stalk, 20–115 mm long , 7–42 mm wide, clasping stem (perfoliate), flat apex, , 5-12 veins on either side of midrib. vary considerably in colour , may bright green, dark green, yellowish, olive or brownish. there no floating leaves. stipules rather delicate , fall off quite after new leaf has unfurled. insignificant flowers produced between june , september. fruits 4 mm across, olive green in colour.

two subspecies have been described. subspecies perfoliatus occurs in old world. in north america, populations on eastern seaboard , gulf states considered subsp. bupleuroides. since many pondweeds, including p. perfoliatus, vary naturally in response growing conditions, possible these variants ecotypes rather genuine subspecies. related p. richardsonii formerly considered subspecies of p. perfoliatus, classed separate species.

like other broadleaved pondweeds, perfoliate pondweed tetraploid, 2n=52.

over of range, perfoliate pondweed unlikely confused other pondweed species except perhaps p. praelongus. in north america confused p. richardsonii, latter has stipules disintegrate persistent fibres on lower part of stem, whereas of p. perfoliatus disintegrate entirely.

however, perfoliate pondweed regularly hybridises other potamogeton species including p. crispus (p. × cooperi (fryer) fryer), p. gramineus (p. × nitens weber), p.lucens (p. × salicifolius wolfg.), p. alpinus (p. × prussicus hagstr.), p. berchtoldii (p. × mysticus morong), p. wrightii (p. × anguillanus koidz.), p. maackianus (p. × leptocephalus koidz.), p. alpinus (p. × prussicus hagstr.), p. nodosus (p. × assidens z. kaplan, zalewska-gałosz et m. ronikier), p. richardsonii (p. × absconditus z. kaplan, fehrer & hellq.), p. epihydrus (p. × versicolor z. kaplan, hellq. , fehrer) , p. praelongus (p. × cognatus asch. & graebn.). first 3 of these quite common. triple hybrid, p. gramineus × lucens × perfoliatus (p. × torssandrii (tiselius) dörfler), known. many of these hybrids perennial , long-lived, occurring in absence of 1 or both parents. therefore, care should taken identification of unusual specimens.