Northern snailseed pondweed, potamot spirille

Rhizomes present. Cauline stems compressed, without spots, 5--40 cm; glands absent. Turions absent. Leaves both submersed and floating or floating absent, ± spirally arranged. Submersed leaves sessile, lax; stipules persistent to deliquescent, inconspicuous, convolute, adnate to blade for ½ stipule length, reddish brown to light green, ligulate, 2--12 mm, not fibrous, not shredding at tip, apex obtuse; blade red-brown to light green, linear, not arcuate, 0.8--8 cm ´ 0.5--2 mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, obtuse to acute, lacunae present, a broad band each side of midvein; veins 1--3. Floating leaves petiolate; petioles continuous in color to apex, 5--25 mm; blade adaxially light green, oblong to obovate, 0.7--—3.5 cm ´ 2--13 mm, base tapered to rounded, apex obtuse, rounded; veins 5--15. Inflorescences unbranched; peduncles dimorphic, submersed axillary, recurved, clavate, 0.5--3 mm, emersed axillary or terminal, erect to recurved, slightly clavate, 4--27 mm; spikes dimorphic, submersed capitate, 2--5 mm, emersed ellipsoid to cylindric, 4--13 mm. Fruits sessile, greenish brown, somewhat orbicular, compressed, abaxially winged, laterally winged, 4--13 ´ 1.3--2.4 mm, lateral wing with blunt tips; beak absent; sides without basal tubercles; embryo with more than 1 full spiral.

Flowering mid summer--late fall. Neutral to acidic waters of ponds, lakes, and streams; 0--400 m; Man., N.B., Nfld. and Labr. (Nfld.), N.S., Ont., P.E.I., Que.; Conn., Iowa, Maine, Mass., Mich., Minn., Nebr., N.H., N.J., N.Y., Ohio, Pa., R.I., Vt., Wis.

The This is the firstone of three Potamogeton species in the flora area with dimorphic inflorescences. It can be separated from the other two species because its submersed leaf blades have broad lacunae, extending nearly from the midvein to the margin, and its fruits have lateral wings with blunt points along it. along them.