Potamogeton bicupulatus Fernald

Potamogeton bicupulatus is an uncommon species of the acid lakes and streams of northeastern United States and southern Canada. It is the final third species we have with dimorphic inflorescences and embryos with more than one full spiral. It can be separated from the other two, Potamogeton spirillus and P. diversifolius, because it has very narrow submersed leaves without lacunae and fruits with lateral keels without sharp points.

Rhizomes present. Cauline stems compressed, without spots, 10--25 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 less than ½ stipule length, light green, ligulate, 0.2--1.2 cm, not fibrous, not shredding at tip, apex obtuse; blade light green to rarely brown, linear-setaceous, not arcuate, 1.5--11 cm ´ 0.1--0.4(--0.6) mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, tapering, lacunae absent; veins 1. Floating leaves petiolate; petioles continuous in color to apex, 5--35 mm; blade adaxially light green, lanceolate-elliptic to broadly elliptic, 0.6--2.3(--2.8) cm ´ 1--11 mm, base tapering or rounded, apex acute to long tapering; veins 3--7. Inflorescences unbranched; peduncles dimorphic, submersed axillary, somewhat recurved, clavate, 1--10 mm, emersed axillary or terminal, erect to slightly recurved, slightly clavate, 3.5--22 mm; spikes dimorphic, submersed , globular to ellipsoid, 1.5--7 mm, emersed ellipsoid to cylindric, 3--14 mm. Fruits sessile, greenish brown, somewhat orbicular, compressed, abaxially keeled, laterally keeled, 1.1--2.1 ´ 1.1--2 mm, lateral keel without points; beak absent; sides without basal tubercles; embryo with more than 1 full spiral.

Ont.; Conn., Del., Ind., Maine, Mass., Mich., N.H., N.Y., Pa., R.I., Tenn., Vt., Va., Wis.

Flowering early summer--fall.

Acidic waters of ponds, lakes, and streams; 0--300m.

Potamogeton diversifolius Rafinesque var. trichophyllus Morong

Potamogeton dimorphus Raf. Am. Mo. Mag. 1 : 358. 1817
i
Potamogeton diversifolius Barton, Fl. Phila. Prodr. 27. 1815. Not P. diversifolius Raf. Potamogeton diversifolius spicalus Engelm. Am. Jour. Sci. 42 : 102. 1844. Potamogeton Spirillus Tuckerm. Am. Jour. Sci. II. 6 : 228. 1848. Potamogeton Spirillus curvifolius Peck, Ann. Rep. N. Y. State Mus. 49 : 28, 1896.
Stem simple or much branched ; floating leaves petioled ; blades coriaceous, ovatelanceolate or oblong-lanceolate, acute or obtuse at the apex, narrowed at the base, 1-2.5 cm. long, 3-8 mm. wide; petioles slender, about as long as the blades, or longer; stipules acute, axillary and free from the petioles, 3-11 mm. long; submerged leaves capillary, 1-1.4 mm. wide, 3-a> cm. long, sometimes recurved ; emersed spikes cylindric, up to 1 cm, long; peduncle 1-3 times as long as the spike ; submerged spikes shorter, almost globose, sessile or nearly so ; nutlets pitted and 3-keeled, the middle keel sometimes winged, but without teeth or bristles ; embryo a complete spiral and coiled 1%, times, the curved apex pointing
inside the base and upward.
Type locality : Pennsylvania.
Distribution : Nova Scotia to Minnesota and California, south to Virginia and Missouri.

Potamogeton bicupulatus là một loài thực vật có hoa trong họ Potamogetonaceae. Loài này được Fernald miêu tả khoa học đầu tiên năm 1932.