Potamogeton obtusifolius Mert. & Kock
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Family: Potamogetonaceae
Genus: Potamogeton
Species Synonyms: none
Common Names: bluntleaf pondweed
Canada: south-central Yukon, southwestern British Columbia, Alberta – Saskatchewan – northern Manitoba – Ontario – Quebec – Newfoundland – Nova Scotia
Saskatchewan: northern to south-central Saskatchewan; Lake Athabasca – Clearwater River – Deschambault Lake – Chelan
Ecoregion: Moist Mixed Grassland, Boreal Transition, Mid-Boreal Upland, Mid-Boreal Lowland, Churchill River Upland, Tazin Lake Upland
Saskatchewan: in shallow water of protected lake bays, ponds, and quiet streams
Canada: cold streams and lakes
Provincial Status According
to Harms (2003):
Nature Conservancy Status:
G5 S2
Saskatchewan Species at
Risk Status:
Potamogeton obtusifolius is threatened because it is rare or uncommon in Saskatchewan. No threats are known or anticipated for this species.
Height: 35 – 90 cm
Roots: roots fibrous; rhizomes absent
Stems: branched, slightly compressed, slender, without spots, glands at nodes yellow-green to gold; turions terminal, abundant, soft
Leaves: submersed, spirally arranged, sessile, flaccid, 3 – 8 cm long, 1 – 4 mm wide, base not lobed, apex rounded or apiculate, light green to reddish, lacunae septate and in 1 – 3 rows on each side of midrib, veins 3, margin entire; stipules persistent, 1 – 2 cm long, convolute, free from blade, fibrous
Inflorescence: spike emersed, 8 – 15 mm long; peduncles 1 – 4 cm long, uniform, erect, cylindrical
Flowers: small, greenish; tepals 4; stamens 4; carpels 4
Fruits: sessile, olive-green to brown, may be keeled, beak short
1 Stipular sheaths of submersed leaves adnate to base of leaf blade; leaf margins cartilaginous
P. robbinsii
1 Stipular sheaths of submersed leaves free from base of leaf blade; leaf margins not cartilaginous
2 Submersed leaves oblong to lanceolate to nearly orbicular
2 Submersed leaves ribbon-like or thread-like
3 Leaf margins conspicuously serrate and undulate; turions present
P. crispus
3 Leaf margins entire or undulate; turions absent
4 Submersed leaves clasping; floating leaves absent
4 Submersed leaves not clasping, may be petiolate; floating leaves present or absent
5 Stipules persistent; rhizome with rusty spots
P. praelongus
5 Stipules shredding into fibres; rhizome not obviously spotted
P. richardsonii
6 Floating leaf blade rounded to cordate; stem rusty or black-spotted; submersed leaves arcuate
P. amplifolius
6 Floating leaf blade cuneate or rounded; stems without spots; submersed leaves not arcuate
7 Submersed leaves petiolate
P. nodosus
7 Submersed leaves sessile
8 Fruits plump, pedicellate; submersed leaf blade 7 – 9-veined
P. alpinus
8 Fruits compressed, sessile; submersed leaf blade 3 – 19-veined
P. gramineus
9 Floating leaves present on at least some plants in a population
9 Floating leaves absent
10 Lacunae present and prominent; submersed leaves with distinction between blade and petiole; leaves dimorphic, the floating ones long-petioled and wider than the submersed ones
P. epihydrus
10 Lacunae absent or not prominent; submersed leaves phyllodial; leaves uniform, no distinction between the floating and submersed leaves
P. natans
11 Nodes without glands
11 Nodes glandular
12 Leaves 15 – 35-veined, greater than 2 mm wide; stem wing-flattened
P. zosteriformis
12 Leaves 3 – 5-veined, less than 2 mm wide; stem not wing-flattened
P. foliosus ssp. foliosus
13 Stipules fibrous, whitish
13 Stipules not fibrous, green, brown or whitish
14 Leaf apex acute to apiculate, leaves thin, 5 – 7-nerved; peduncles at most 5 cm long
P. friesii
14 Leaf apex bristle-tipped; leaves firm, 3-nerved; peduncles to 9 cm long
P. strictifolius
15 Fruits 2.5 – 3.5 mm long
P. obtusifolius
15 Fruits 1.5 – 2 mm long
16 Mature fruits obovoid; peduncles 1 – 3 per plant; leaf blade with less than 2 rows of lacunae along midrib
P. pusillus ssp. pusillus
16 Mature fruits widest at the middle; peduncles more than 3 per plant; leaf blade with 1 – 5 rows of lacunae along midrib
P. pusillus ssp. tenuissimus