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Ceratophyllum demersum : ウィキペディア英語版 | Ceratophyllum demersum
''Ceratophyllum demersum'', commonly known as hornwort, rigid hornwort, coontail, or coon's tail,〔 is a species of ''Ceratophyllum''. It is a submerged, free-floating aquatic plant, with a cosmopolitan distribution, native to all continents except Antarctica. It is a harmful introduced weed in New Zealand.〔(Ceratophyllum Demersum ) on the Global Invasive Species database (2006).〕 It is also a popular aquarium plant. ==Description== An aquatic plant, ''Ceratophyllum demersum'' has stems that reach lengths of , with numerous side shoots making a single specimen appear as a large, bushy mass. The leaves are produced in whorls of six to twelve, each leaf 8–40 mm long, simple, or forked into two to eight thread-like segments edged with spiny teeth; they are stiff and brittle. It is monoecious, with separate male and female flowers produced on the same plant. The flowers are small, 2 mm long, with eight or more greenish-brown petals; they are produced in the leaf axils. The fruit is a small nut 4–5 mm long, usually with three spines, two basal and one apical, 1–12 mm long. Plants with the two basal nut spines very short are sometimes distinguished as ''Ceratophyllum demersum'' var. ''apiculatum'' (Cham.) Asch., and those with no basal spines sometimes distinguished as ''Ceratophyllum demersum'' var. ''inerme'' Gay ex Radcl.-Sm.〔Flora of China: (''Ceratophyllum demersum'' )〕〔Flora of North America: (''Ceratophyllum demersum'' )〕〔Flora of NW Europe: (''Ceratophyllum demersum'' )〕〔Blamey, M. & Grey-Wilson, C. (1989). ''Flora of Britain and Northern Europe''. ISBN 0-340-40170-2〕〔Huxley, A., ed. (1992). ''New RHS Dictionary of Gardening''. Macmillan ISBN 0-333-47494-5.〕 It can form turions: buds that sink to the bottom of the water that stay there during the winter and form new plants in spring.
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