4. Myriophyllum sibiricum Kom. (common water-milfoil)

M. exalbescens Fernald

M. spicatum var. exalbescens (Fernald) Jeps.

Map 1896

Plants mostly monoecious (with occasional perfect flowers). Stems branched, variously slender or stout, uniform in diameter throughout, with only the inflorescence extending above the surface of the water, the median internodes 8–30 mm long, white to tan or rarely reddish-tinged toward the tip. Leaves all in whorls of (3–)4–6, sessile or nearly so, grayish green, seasonally sometimes brownish-tinged. Emergent leaves (bracts) much smaller than the submerged leaves, 1.5–2.0 mm long, the blade elliptic to narrowly obovate, the margins entire or the lower ones inconspicuously toothed, the bracteal leaves equal to or shorter than the associated flowers. Submerged leaves 10–50 mm long, the blade pinnately divided, narrowly to broadly ovate in outline, the segments (6–)10–22, variously 1–12 mm long (the median divisions more than 6 mm long). Inflorescences appearing as spikes. Flowers appearing white or pinkish- to reddish-tinged, the bractlets ovate to triangular, entire toothed. Petals of staminate and perfect flowers not translucent. Stamens 8, the anthers 1.2–1.8 mm long. Fruits 2–3 mm long, ovoid to subglobose, the surfaces of the nutlets smooth or roughened with minute tuberculate ridges. 2n=42. June–September.

Uncommon, widely scattered in the southern half of the state (northern U.S. [including Alaska] south to Virginia, Oklahoma, and California; Greenland, Europe). Ponds and lakes.

Paradoxically, M. sibiricum is less common in Missouri than the noxious M. spicatum. See the treatment of that species for further discussion on distinctions between the two taxa. The status of M. sibiricum in Missouri is open to interpretation. It was first collected in the state by Grant Pyrah in 1979 from a lake in Douglas County and thus may be considered a recent introduction in Missouri. However, as a taxon native in adjacent states that presumably expanded its range into Missouri by natural vectors (waterfowl), it probably is more reasonable to consider it a native addition to the flora.