Myriophyllum dicoccum F.Muell.

Aquatic. Stem branched, freely floating. Immersed leaves in whorls of 4-5, 1½-2½ by c. 1 cm in outline, patent to recurved, with 4-7(-10) pairs of filiform, rather weak, brown-tipped, finely mucronate, 5-10 mm long segments. Lower aerial leaves verticillate or alternate, pinnate, the upper ones obovate-oblong to linear-lanceolate, above the middle with 2-4(-7) pairs of dark mucronate teeth, sometimes entire, patent, upward erecto-patent, 10-25 by 1-3 mm. Flowers solitary in the middle and upper leaf-axils, or together with 1 or more reduced, cleisto-gamous flower(s), ☿, on a shortly cylindrical, up to ½ mm long pedicel. Bracteoles ± elliptic, with appressed, brown, serrate teeth, acute, with 1-3 nerves, 1½-2 by 0.4-0.8 mm. Sepals ± ovate obtuse or acute, serrate, with a brown margin, erect, 0.2-0.5 by 0.2-0.5 mm. Petals patent to recurved in anthesis, finally caducous, c. 2 mm long. Stamens 4, rarely 8; anthers stiffly erect, linear lanceolate, c. 1½ by 0.3 mm, with brown mucronate apex. Ovary 2-celled, with 1(-2) ovules in each cell, sometimes 3-4-celled with 1 ovule in each cell. Styles 2(-4), 0.2-0.4 by 0.2 mm. Stigma not or slightly recurved. Fruit c. 1½ by 1 mm, with 2, sometimes 3 or 4 mericarps, smooth or indistinctly lengthwise lineolate, with a c. 0.5 by 0.4 mm long, erect or patent stalk. Cleistogamous flowers: without perianth segments, ovary 2-celled, ± circular, laterally flattened, with 2 ovules, fruit c. ½ by ½ mm, with 2 elliptic seeds; bracteoles ovate, c. ½ by 0.4 mm; pedicel up to 4 mm in fruit.

In lake, at 15 m.

Can be grown by cuttings.