Myriophyllum pedunculatum Hook.F.

Terrestrial or semi-aquatic, whether or not growing in dense cushions. Stem unbranched to much branched, decumbent or erect, after anthesis monopodially accrescent. Leaves opposite, erecto-patent to reflexed, entire, rarely pinnate, the entire ones linear, (2-)4-15(-25) by 0.4-1 mm, obtuse to mucronate, above at apex with an ovate, darker coloured cushion-like thickening c. 0.2 mm long. Flowers solitary in the middle and upper leaf-axils, the lower often bearing the fruits of the last season; the upper 2-4(-8) flowers ♂, the next lower 4-8 (-12) flowers ♀; not rarely dioecious. Bracteoles lanceolate-oblong to linear-lanceolate, rarely ± elliptic, acute or acuminate, entire or serrate, 0.6-1.5 by 0.2-0.3(-0.6) mm. ♂ Flowers: up to ½ mm stalked. Sepals lanceolate, acute, serrate, c. 1 by 0.4 mm, ± erect, with tiny whitish tubercles. Petals very concave in the apical part, the borders nearly flat, and finely serrate, the apex mucronate and often recurved, in anthesis erect and 1-1½ mm long, after anthesis elongating, up to 2 mm long, recurvate, persistent. Stamens 8; anthers oblong, c. 1-1½ mm. Ovary rudimentary, c. 0.3 by 0.3 mm. ♀ Flowers: up to 0.2 mm stalked. Sepals lanceolate-oblong, acute, 0.3-0.8 by 0.2 mm. Petals strongly reduced, covered by the styles, shorter than 0.1 mm. Styles with thick, fleshy bases, stigmas after anthesis strongly ligulately recurved, very long papillose. Fruit c. 1.2 by 1.2 mm, with apically spreading mericarps, these terete, with distinct tubercles.

In New Guinea in the upper montane and alpine zone, from 2300-3500 m, in the Australian region often descending to the lowland. In swamps, shallow pools, alpine bogs, and inundated river banks.