Myriophyllum triphyllum Orchard

Perennial herb; stems 50-100 cm long, weak, simple or branched. Lvs dimorphic, whorled. Submerged lvs in whorls of (2)-3-(4), ovate, subsessile, (6)-10-15 × (5)-7-10-(15) mm, pectinate; pinnae 12-18, filiform, c. 8 mm long. Aerial lvs red-purple, in whorls of 3-(4), narrowly ovate to obovate, (2.5)-5-6-(12) × (1.5)-2-2.5-(4) mm, usually entire (lower or transitional lvs sometimes incised), obtuse. Fls solitary in axils of the aerial lvs, unisexual, the upper ♂, the lower ♀. Bracteoles lanceolate, (1)-1.4-1.8-(2) × (0.2)-0.3-0.4 mm. ♂ fls: sepals 4, 0.5-0.6 × 0.4-0.5 mm, deltoid; petals 4, hooded, 2-2.8 × c. 2 mm. ♀ fls: sepals 4, c. 0.2 × 0.2 mm; petals 4, c. 0.5 mm long. Frs ± globular or cubiform, 1.3-1.4-(1.5) × 1.4-1.5 mm, smooth and rounded on dorsal surface of mericarps, sometimes with a faint dorsal line.