Perennial aquatic herb
Stem: mostly submersed, unbranched or with few long branches to 2.5 m long.
Leaves: in whorls of four to five, pinnately divided. Submersed leaves are 0.8 - 4.5 cm long with nine to seventeen divisions on each side. Emersed leaves and bracts are smaller and more coarsely divided.
Flowers: either male or female, found on the same plant (monoecious), some bisexual, borne in whorls of four to six on a terminal spike above the water surface, with male flowers near inflorescence tip. Pinnate or incompletely pinnate bracts extend past the flowers. Small, greenish, four-parted, petals are poorly developed in female flowers and yellowish green in male flowers, which have eight stamens.
Fruit: a deeply four-lobed nut-like cluster, 2 - 2.5 mm long, nearly spherical, splitting into four segments, each segment brown and deeply four-furrowed with a round back.
Winter buds: well-formed, 1 - 2 cm long, club-shaped, falling off in early winter.
Similar species: Myriophyllum sibiricum and Myriophyllum spicatum differ by having non-toothed or toothed bracts that are shorter than the flower. Myriophyllum pinnatum is easy to distinguish by having both alternate and whorled leaves. Myriophyllum heterophyllum has four stamens on its male flowers, toothed or non-toothed bracts, and winter buds formed at the base of stems or on rhizomes.
Flowering: mid July to late August
Habitat and ecology: Rare in lakes and streams.
Occurence in the Chicago region: native
Etymology: Myriophyllum comes from the Greek words, myrios, meaning many, and phyllon, meaning leaf, referring to its highly divided leaves. Verticillatum means whorled.
Author: The Morton Arboretum
