Variable-leaf watermilfoil

Submersed Plants

Myriophyllum heterophyllum:

Variable-leaf watermilfoil

Myriophyllum heterophyllum Michx.: Variable-leaf water milfoil, two-leaf milfoil, foxtail. Haloragaceae (watermilfoil family). 

Native perennial. Rhizomes buried in the substrate produce roots and stout reddish stems (0.1 in, 3 mm, thick). Stems grow to 6 ft (1.8 m) under water; upon reaching the surface they can emerge up to 6 in (15 cm). The submersed and emergent stems have distinctly different leaf forms. Underwater leaves are arranged in close whorls of usually 5 to 6. They are up to 2.5 in (6 cm) long and consist of very slender, soft, thread-like divisions projecting on either side of a central midrib; there are from 6 to 14 of these leaflet divisions per side. The underwater stem forms a dense tuft at its tip and resembles a soft bottlebrush. As the stem reaches the surface it changes its growth pattern to become a stout emergent flower-spike carrying an entirely different type of leaf (actually a bract). These emergent leaves are stalkless, wedge-shaped, stiff, and pointed, with variably-toothed margins; they are up to 1.2 in (3 cm) long. Inconspicuous flowers are borne just above the bases of these leaves. The plant can form dense growth, rooting from stem fragments, and reaches nuisance levels in some regions.