Burke: Potamogeton alpinus vs. Potamogeton robbinsii

	Potamogeton alpinus	Potamogeton robbinsii
	northern pondweed, reddish pondweed	fern pondweed, Robbin's 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 terete, stout, branching, 1-4 dm. 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, submersed, linear-lanceolate, up to 12 cm. long, mostly 3-4 mm. broad, acute, finely serrulate, with a broad mid-nerve and 20-35 very fine lateral nerves, stiffly 2-ranked and crowded on the stem; stipules fused to the leaf bases for 10-15 mm., the free portion longer, white.
Flowers	Inflorescence generally < 3 cm, floating to emergent; peduncle stiff.	Stem freely-branching in the inflorescence, with many peduncles 3-5 cm. long; flowers perfect, in spikes 7-20 mm. long on the peduncles; 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 obovoid, 3.5-4 mm. long, with a sharp dorsal keel and rounded lateral keels, and without a beak.

	Potamogeton alpinus	Potamogeton robbinsii
Flowering time	June-August	August - September
Habitat	Calm water of lakes and slow streams.	Quiet water, mostly in lakes.
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; Alaska to California, east to Montana and Colorado; Minnesota to Maine, south to Virginia in eastern United States. [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. illinoensis, P. natans, P. nodosus, P. obtusifolius, P. praelongus, P. pusillus, P. richardsonii, 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 robbinsii

northern pondweed, reddish pondweed

fern pondweed, Robbin's 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 terete, stout, branching, 1-4 dm. 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, submersed, linear-lanceolate, up to 12 cm. long, mostly 3-4 mm. broad, acute, finely serrulate, with a broad mid-nerve and 20-35 very fine lateral nerves, stiffly 2-ranked and crowded on the stem;

stipules fused to the leaf bases for 10-15 mm., the free portion longer, white.

Flowers

Inflorescence generally < 3 cm, floating to emergent;

peduncle stiff.

Stem freely-branching in the inflorescence, with many peduncles 3-5 cm. long;

flowers perfect, in spikes 7-20 mm. long on the peduncles;

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 obovoid, 3.5-4 mm. long, with a sharp dorsal keel and rounded lateral keels, and without a beak.

Potamogeton alpinus

Potamogeton robbinsii

Flowering time

June-August

August - September

Habitat

Calm water of lakes and slow streams.

Quiet water, mostly in lakes.

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; Alaska to California, east to Montana and Colorado; Minnesota to Maine, south to Virginia in eastern United States.

[WildflowerSearch map]

[BONAP county map]

Origin

Native

Conservation status

Not of concern

Sibling taxa