UW Burke Herbarium species comparison

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Potamogeton robbinsii

Potamogeton oakesianus

fern pondweed, Robbin's pondweed
Habit Aquatic, herbaceous perennials from slender rhizomes, the stems terete, stout, branching, 1-4 dm. long.
Leaves

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

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.

Fruits

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

Potamogeton robbinsii

Potamogeton oakesianus
Flowering time August - September
Habitat Quiet water, mostly in lakes.
Distribution
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]
[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. foliosus, P. friesii, P. gramineus, P. illinoensis, P. natans, P. nodosus, P. obtusifolius, P. praelongus, P. pusillus, P. richardsonii, 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 
Unless otherwise noted, all data comes from the University of Washington's Burke Herbarium.



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