Potamogeton amplifolius Tuckerman
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Family: Potamogetonaceae
Genus: Potamogeton
Species Synonyms: none
Common Names: largeleaf pondweed
broad-leaved pondweed
Canada: south-central British Columbia, central Saskatchewan – Manitoba – Ontario – Quebec – Newfoundland – Nova Scotia
Saskatchewan: central Saskatchewan; Prince Albert National Park – Churchill River
Ecoregion: Mid-Boreal Upland, Churchill River Upland
Saskatchewan: in shallow quiet water of protected lake bays, ponds, and slow-moving streams
Canada: lakes and streams
Provincial Status According
to Harms (2003):
Nature Conservancy Status:
G5 S1
Saskatchewan Species at
Risk Status:
Largeleaf pondweed is endangered because of extreme rarity in Saskatchewan. No immediate threats are known but may occur in the future.
Height: 6 – 100 cm
Roots: roots fibrous; rhizomes present
Stems: round, often rusty spotted
Leaves: both submersed and floating, floating leaves may be absent; submersed leaves 5 – 12 cm long, 1.5 – 6 cm wide, oval to inversely lance-shaped, base rounded to acute, not clasping, lax, light to dark green, veins 20 – 50, margin entire; stipular sheaths persistent, conspicuous, free from the base of the leaf blade, light brown, not fibrous or shredding at tip; petioles to 6 cm long, round; floating leaves stalked, 4 – 9 cm long, 2.5 – 4 cm wide, lance-shaped to elliptic, base rounded to heart-shaped, veins 27 – 50
Inflorescence: spikes terminal or axillary, erect, 3.5 – 8 cm long, cylindrical, uniform, floating; inflorescence stalks uniform
Flowers: small, greenish; tepals 4; stamens 4; ovaries 4
Fruits: single-seeded, sessile, reddish-brown, with a prominent central beak
1 Stipular sheaths of submersed leaves fused 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 lance-shaped to nearly round
2 Submersed leaves ribbon-like or thread-like
3 Leaf margins conspicuously saw-toothed and wavy; overwintering stems present
P. crispus
3 Leaf margins entire or wavy; overwintering stems absent
4 Submersed leaves clasping; floating leaves absent
4 Submersed leaves not clasping, may be stalked; 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 heart-shaped; stem rusty or black-spotted; submersed leaves arced
P. amplifolius
6 Floating leaf blade wedge-shaped or rounded; stems without spots; submersed leaves not arced
7 Submersed leaves stalked
P. nodosus
7 Submersed leaves sessile
8 Fruits plump, stalked; submersed leaf blade 7 – 9-veined
P. alpinus
8 Fruits compressed, not stalked; submersed leaf blade 3 – 19-veined
P. gramineus
9 Floating leaves present on at least come plants in a population
9 Floating leaves absent
10 Air spaces in leaf tissue present and prominent; submersed leaves with distinction between blade and stalk; leaves of two types, the floating ones long-stalked and wider than the submersed ones
P. epihydrus
10 Air spaces in leaf tissue absent or not prominent; blade and petiole not well-differentiated on submersed leaves; 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 tip tapered to pointed, leaves thin, 5 -7-nerved; inflorescence stalks at most 5 cm long
P. friesii
14 Leaf tip bristle-tipped; leaves firm, 3-nerved; inflorescence stalks 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 widest at the top; inflorescence stalks 1 – 3 per plant; leaf blade with less than 2 rows of air spaces along midrib
P. pusillus ssp. pusillus
16 Mature fruits widest at the middle; inflorescence stalks more than 3 per plant; leaf blade with 1 – 5 rows of air spaces along midrib
P. pusillus ssp. tenuissimus