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''Potamogeton'' × ''angustifolius'' is a hybrid pondweed between ''Potamogeton gramineus'' and ''Potamogeton lucens'', known as long-leaved pondweed. It is widepread in rivers and lakes except where the water is very soft. ==Description== ''Potamogeton'' × ''angustifolius'' is a hybrid between shining pondweed ''Potamogeton lucens'' and various-leaved pondweed ''Potamogeton gramineus''. It is a perennial, growing from robust rhizomes. The stems are variable: slender to robust, terete, and branching, usually reaching 1.2 m but rarely up to 2m.〔 The submerged leaves are reduced to phyllodes at the base of the stem, but elsewhere are broad and translucent, yellowish to dark green, sometimes with a pinkish tinge. The leaves measure 50-130 × 10-25 mm on the stems and main branches, but may be much smaller on the side branches; they have 4-5 (rarely 6) veins either side of the midrib and are usually sessile but some clones may have a few petiolate leaves. Turions are absent. Unlike ''P. lucens'', ''Potamogeton'' × ''angustifolius'' sometimes produces floating leaves, which are opaque and typically 55-105 × 22-40 mm.〔 The stipules are persistent, open, green when fresh, drying to olive or brownish.〔 The inflorescences are 20-50 mm long and have inconspicuous greenish flowers on robust peduncles 45–190 mm long.〔 Fruits are not always produced; if present they are approximately 3 × 2 mm.〔 Identification of ''Potamogeton'' × ''angustifolius'' may require experience. It is larger and more robust than ''P. gramineus'' but more slender and graceful than ''P. lucens''. There is a tendency for main stems to more closely resemble ''P. lucens'', and side branches ''P. gramineus''. There is however no single character to identify this hybrid, and accurate determination is likely to rely on a combination of characters.〔 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 × angustifolius」の詳細全文を読む スポンサード リンク
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