Burke: Potamogeton foliosus vs. Potamogeton vaseyi

	Potamogeton foliosus	Potamogeton vaseyi
	leafy pondweed
Habit	Aquatic, herbaceous perennials from slender rhizomes, the stems freely branching, somewhat compressed and narrow winged, scarcely 1 mm. broad, up to 10 dm. long.
Leaves	Leaves all submersed, without basal glands, narrowly linear, 1-1.5 mm. broad and up to 10 cm. long, acute, 3-nerved, bordered toward the base with air chambers; stipules united and surrounding the stem, 5-15 mm. long, ultimately disintegrating.
Flowers	Inflorescence of spikes up to 5 mm. long with 2-3 whorls of crowded, sessile flowers; peduncles stout, rarely over 2 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 obovoid, 2 mm. long, with a prominent dorsal keel.

	Potamogeton foliosus	Potamogeton vaseyi
Flowering time	June-August
Habitat	Standing to moving, shallow water.
Distribution	Occurring on both sides of the Cascades crest in Washington; Alaska to California, east across North America to the Atlantic Coast. [WildflowerSearch map] [BONAP county map]	[WildflowerSearch map] [BONAP county map]
Origin	Native
Conservation status	Not of concern
Sibling taxa	P. alpinus, P. amplifolius, P. berchtoldii, P. crispus, P. epihydrus, P. fibrillosus, 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 foliosus

Potamogeton vaseyi

leafy pondweed

Habit

Aquatic, herbaceous perennials from slender rhizomes, the stems freely branching, somewhat compressed and narrow winged, scarcely 1 mm. broad, up to 10 dm. long.

Leaves

Leaves all submersed, without basal glands, narrowly linear, 1-1.5 mm. broad and up to 10 cm. long, acute, 3-nerved, bordered toward the base with air chambers;

stipules united and surrounding the stem, 5-15 mm. long, ultimately disintegrating.

Flowers

Inflorescence of spikes up to 5 mm. long with 2-3 whorls of crowded, sessile flowers;

peduncles stout, rarely over 2 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 obovoid, 2 mm. long, with a prominent dorsal keel.