Burke: Potamogeton alpinus vs. Potamogeton illinoensis

	Potamogeton alpinus	Potamogeton illinoensis
	northern pondweed, reddish pondweed	illinois pondweed
Habit	Annual, perennial herb, slender, rhizomed; stems greater than 100 cm, branched, branches not many, cylindric.	Aquatic, herbaceous perennials from slender rhizomes, the stems simple to freely branched, terete, up to 2 m. long.
Leaves	Various shades of red; submersed sessile, 2-8 x 1-2 cm, lanceolate to elliptic-oblong, tapered to both ends, entire, tip blunt, veins 7-9; floating 0 or short-petioled, lanceolate, base tapered, veins 7-15; stipules beyond 3 cm, free, membranous, early-deciduous.	Leaves alternate, the submersed leaves thin, lanceolate to elliptic or oblanceolate, 10-20 cm. long and 2-4 cm. broad, sub-sessile or tapered to a short petiole, prominently 9- to 19-nerved; floating leaves, if any, rather firm, transitional to the submersed leaves; stipules 3-7 cm. long.
Flowers	Inflorescence generally < 3 cm, floating to emergent; peduncle stiff.	Flowers perfect, in compactly-flowered spikes 3-6 cm. long, on peduncles 4-12 cm. long, thicker than the stem; perianth of 4 clawed segments, each with an upturned, oval blade; stamens 4, fused with the claws; pistils 4, sessile.
Fruit(s)	Around 2.5 mm, keels 1 or 3, generally, beaked, sides concave to convex.	Achenes broadly obliquely obovoid, 4 mm. long including the short beak, the dorsal keel prominent and sharp, the lateral keels also prominent.

	Potamogeton alpinus	Potamogeton illinoensis
Flowering time	June-August	May-August
Habitat	Calm water of lakes and slow streams.	Ponds and lakes, usually in rather deep, quiet water.
Distribution	Occurring on both sides of the Cascades crest in Washington; Alaska to California, east to the Rocky Mountains and northern Great Plains; also in eastern North America. [WildflowerSearch map] [BONAP county map]	Occurring on both sides of the Cascades crest in Washington; Northwest Territories to California, east across much of North America to the Atlantic Coast. [WildflowerSearch map] [BONAP county map]
Origin	Native	Native
Conservation status	Not of concern	Not of concern
Sibling taxa	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	P. alpinus, P. amplifolius, P. berchtoldii, P. crispus, P. epihydrus, P. fibrillosus, P. foliosus, P. friesii, P. gramineus, 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 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

Potamogeton illinoensis

northern pondweed, reddish pondweed

illinois pondweed

Habit

Annual, perennial herb, slender, rhizomed; stems greater than 100 cm, branched, branches not many, cylindric.

Aquatic, herbaceous perennials from slender rhizomes, the stems simple to freely branched, terete, up to 2 m. long.

Leaves

Various shades of red; submersed sessile, 2-8 x 1-2 cm, lanceolate to elliptic-oblong, tapered to both ends, entire, tip blunt, veins 7-9; floating 0 or short-petioled, lanceolate, base tapered, veins 7-15;

stipules beyond 3 cm, free, membranous, early-deciduous.

Leaves alternate, the submersed leaves thin, lanceolate to elliptic or oblanceolate, 10-20 cm. long and 2-4 cm. broad, sub-sessile or tapered to a short petiole, prominently 9- to 19-nerved; floating leaves, if any, rather firm, transitional to the submersed leaves;

stipules 3-7 cm. long.

Flowers

Inflorescence generally < 3 cm, floating to emergent;

peduncle stiff.

Flowers perfect, in compactly-flowered spikes 3-6 cm. long, on peduncles 4-12 cm. long, thicker than the stem;

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

stamens 4, fused with the claws;

pistils 4, sessile.

Fruit(s)

Around 2.5 mm, keels 1 or 3, generally, beaked, sides concave to convex.

Achenes broadly obliquely obovoid, 4 mm. long including the short beak, the dorsal keel prominent and sharp, the lateral keels also prominent.

Potamogeton alpinus

Potamogeton illinoensis

Flowering time

June-August

May-August

Habitat

Calm water of lakes and slow streams.

Ponds and lakes, usually in rather deep, quiet water.

Distribution

Occurring on both sides of the Cascades crest in Washington; Alaska to California, east to the Rocky Mountains and northern Great Plains; also in eastern North America.

[WildflowerSearch map]

[BONAP county map]

Occurring on both sides of the Cascades crest in Washington; Northwest Territories to California, east across much of North America to the Atlantic Coast.

[WildflowerSearch map]

[BONAP county map]

Origin

Native

Conservation status

Not of concern

Sibling taxa