Perennial aquatic or semi-aquatic herb Stem: highly variable, rooting in mud and freely branching or elongating in deeper water. Leaves: alternate and whorled on same plant, pinnately divided, with submersed leaves having three to five pairs of divisions. Emersed leaves are 0.5 - 3 cm long, linear to lance-shaped, and have comb-like divisions or sharp teeth. Flowers: either male or female, found on the same plant (monoecious), some bisexual, borne in a terminal spike above the water surface, with male flowers near the inflorescence tip. Bracts are longer than male flowers, triangular, with six to ten 1 - 2 mm long teeth that are angled toward the tip. Flowers green to purplish, small, four-parted, with 1.5 - 2 mm long petals that are rounded above and narrow-clawed. Fruit: a deeply four-lobed nut-like cluster, pale, 1.3 - 2 mm long, egg-shaped to cubic, splitting into four one-seeded segments that are flat-sided with two spiked ridges. Winter buds: absent.
Similar species: Myriophyllum pinnatum is easy to distinguish from the other Myriophyllum species by having both alternate and whorled leaves, while the other species have only whorled leaves.
Habitat and ecology: Rare in our region, growing in shallow water of ditches and ponds.
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. Pinnatum means feather-like.
Author: The Morton Arboretum
From Flora of Indiana (1940) by Charles C. Deam
Our only recent report for this species is from Jasper County where I found it in the old channel of the Kankakee River half a mile west of the Tefft Bridge. It is doubtless very rare in Indiana.
Lvs partly or largely alternate or scattered, 1-3 cm, with capillary segments; emersed lvs sometimes developing and resembling the bracts, these chiefly whorled, much exceeding the fls, to 18 mm, with a flat rachis to 1 mm wide and on each side 3-5 ascending teeth 1-2 mm; spikes emersed; fr 2 mm, deeply lobed, each mericarp bearing a flat or concave longitudinal ridge with sharply tuberculate margins. Mass. to O., Io., and S.D., s. to Ga. and Tex., more abundant southward. (M. scabratum)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.