Flora of New Zealand Series

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.

N.; S.; St.; Ch., A., C., M.

Endemic.

Still and slowly moving water from sea level to subalpine situations.

M. triphyllum may grow in shallow water but is often found in deeper water than other Myriophyllum spp. in N.Z. It has been previously known in N.Z. as M. elatinoides, a synonym of the distinct S. American sp. A. quitense Kunth (Orchard, op. cit.).