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''Potamogeton gramineus'' is a species of aquatic plant known by the common name various-leaved pondweed, variableleaf pondweed, grass-leaved pondweed or grassy pondweed, native to the northern hemisphere where it grows in shallow, clean water. ==Description== This is an aquatic perennial growing from a creeping rhizome that anchors in wet substrate. It produces thin, cylindrical, heavily branching stems usually less than a metre in length. The submerged leaves are sessile, relatively narrow, typically 40–90 mm long and 5–12 mm wide along the main stem but smaller on the side branches.〔 They are translucent and pale green with a white midrib, and finely toothed. Floating leaves are more oval in shape, 20–70 mm long by 7–34 mm wide,〔 and borne on long petioles. The inflorescence is a short spike of many flowers arising from the water on a stout peduncle. This species readily hybridizes with many other species of ''Potamogeton''. Hybrids have been recorded with ''P. perfoliatus'' (''P''. × ''nitens'' Weber), ''P. lucens'' (''P.'' × ''angustifolius'' J.Presl.), ''P. natans'' (''P''. × ''sparganiifolius'' Laest. ex Fr.), ''P. coloratus'' (''P''. × ''billupsii'' Fryer), ''P. maackianus'' (''P.'' × ''biwaensis'' Miki), ''P. illinoensis'' (''P.'' × ''spathuliformis'' (J.W.Robbins) Morong), ''P. richardsonii'' (''P.'' × ''hagstromii'' A.Benn.), ''P. alpinus'' (''P.'' × ''nericius'' Hagstr.), ''P. nodosus'' (''P.'' × ''lanceolatifolius'' (Tiselius) C.D.Preston), ''P. oakesianus'' (''P.'' × ''mirabilis'' Z.Kaplan, Hellq. & Fehrer) and ''P. polygonifolius''.〔〔 In Britain, ''P''. x ''nitens'' and ''P''. x ''angustifolius'' are quite common. Recent molecular analysis has shown that Swedish collections of the putative hybrid ''P. gramineus'' x ''P. polygonifolius'' are in fact ''P. gramineus'' x ''P. nodosus''.〔 A triple hybrid, ''P. gramineus'' × ''lucens'' × ''perfoliatus'' (''P''. × ''torssandrii'' (Tiselius) Dörfler), is also known. As well as hybridising frequently, various-leaved pondweed is an extremely variable plant and care should be taken with its identification.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Potamogeton gramineus」の詳細全文を読む スポンサード リンク
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