Burke: Potamogeton epihydrus vs. Potamogeton oblongus

	Potamogeton epihydrus	Potamogeton oblongus
	ribbon-leaved pondweed
Habit	Aquatic, perennial herbs from slender rhizomes, the stems somewht flattened, simple or sparingly branched, 5-15 dm. long.
Leaves	Submersed leaves linear, sessile, 10-20 cm. long and 3-10 mm. broad, the mid-vein bordered by rows of air chambers; floating leaves with flattened petioles shorter than the blade, the blades firm, elliptic to oblong-elliptic, 4-8 cm. long and 10-20 mm. broad, 15- to 25-nerved; stipules free, 1-3 cm. long, blunt.
Flowers	Flowers in dense spikes 2-4 cm. long, on peduncles 3-8 cm. long; perianth of 4 clawed segments, each with an upturned, oval blade; stamens 4, fused with the claws; pistils 4, sessile.
Fruits	Achenes obliquely and broadly obovate, 3-4 mm. long, sharply keeled on the back.

	Potamogeton epihydrus	Potamogeton oblongus
Flowering time	June-August
Habitat	Shallow to deep water.
Distribution	Occurring on both sides of the Cascades crest in Washington; Alaska to California, east to the Rocky Mountains; also in northeastern North America; Europe. [WildflowerSearch map] [BONAP county map]	[BONAP county map]
Origin	Native
Conservation status	Not of concern
Sibling taxa	P. alpinus, P. amplifolius, P. berchtoldii, P. crispus, P. fibrillosus, P. foliosus, P. friesii, P. gramineus, P. illinoensis, P. natans, P. nodosus, P. obtusifolius, P. praelongus, P. pusillus, P. richardsonii, P. robbinsii, P. strictifolius, P. zosteriformis	P. alpinus, P. amplifolius, P. berchtoldii, P. crispus, P. epihydrus, P. fibrillosus, P. foliosus, P. friesii, P. gramineus, P. illinoensis, P. natans, P. nodosus, P. obtusifolius, P. praelongus, P. pusillus, P. richardsonii, P. robbinsii, P. strictifolius, P. zosteriformis
Web links	Local floras: BC, CA, OR, WA Local Web sites: CalFlora, CalPhotos, Flora NW, PNW Herbaria WildflowerSearch iNaturalist (observations) USDA Plants Database LBJ Wildflower Center SEINet Plants of the World Online Encyclopedia of Life Wikipedia Google Image Search	Local Web sites: Flora NW, PNW Herbaria WildflowerSearch iNaturalist (observations) USDA Plants Database LBJ Wildflower Center SEINet Plants of the World Online Encyclopedia of Life Wikipedia Google Image Search

Potamogeton epihydrus

Potamogeton oblongus

ribbon-leaved pondweed

Habit

Aquatic, perennial herbs from slender rhizomes, the stems somewht flattened, simple or sparingly branched, 5-15 dm. long.

Leaves

Submersed leaves linear, sessile, 10-20 cm. long and 3-10 mm. broad, the mid-vein bordered by rows of air chambers; floating leaves with flattened petioles shorter than the blade, the blades firm, elliptic to oblong-elliptic, 4-8 cm. long and 10-20 mm. broad, 15- to 25-nerved;

stipules free, 1-3 cm. long, blunt.

Flowers

Flowers in dense spikes 2-4 cm. long, on peduncles 3-8 cm. long;

perianth of 4 clawed segments, each with an upturned, oval blade;

stamens 4, fused with the claws;

pistils 4, sessile.

Fruits

Achenes obliquely and broadly obovate, 3-4 mm. long, sharply keeled on the back.

Potamogeton epihydrus

Potamogeton oblongus

Flowering time

June-August

Habitat

Shallow to deep water.

Distribution

Occurring on both sides of the Cascades crest in Washington; Alaska to California, east to the Rocky Mountains; also in northeastern North America; Europe.

[WildflowerSearch map]

[BONAP county map]

Origin

Native

Conservation status

Not of concern

Sibling taxa