Submersed Plants

 
Species: Potamogeton praelongus Wulfen, white-stemmed pondweed
Potamogeton richardsonii (A. Bennett) Rydb., Richardson's pondweed
Family: Potamogetonaceae

Both species have broad, wavy-edged underwater leaves with leaf bases that wrap part way around the stem and no floating leaves. The leaves of white-stemmed pondweed have prow shaped tips and are longer than those of Richardson's pondweed. Richardson's pondweed leaves are often green and white banded. White-stemmed pondweed is often the first pondweed seen in early spring.

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Leaf: Submersed, alternate, stalkless, with heart-shaped bases that clasp the stem. White-stemmed: shiny leaves, 5-35 cm long and 1.5-2.5 cm wide, often appear wavy or twisted with hooded or prow-shaped leaf tips. Leaves are widest below the middle of the leaf with 5 or more distinct veins. Sheaths (stipules) are stiff, whitish, 3-10 cm long and arise from leaf bases. Richardson's: densely spaced, lance shaped leaves, 2-13 cm long, 1-3 cm wide, have wavy or crinkled margins often curved backwards, with 7 or more veins. Membranous sheaths (stipules) less than 2 cm long, arise from leaf bases, disintegrating or become fibrous early in the growing season.

Stem: White-stemmed: whitish, zigzag branching toward the top, to 3 m long, 2-3 cm thick. Richardson's: often branched, rarely zigzagged, to 1 m long.

Flower: Small, clustered on whorls on emergent spikes. White-stemmed: in 6-12 whorls on spikes up to 5 cm long; flower stalks to 0.5 m long.
Richardson's: in 4-12 whorls on short spikes 2-4 cm long; flower stalks generally just longer than the spike, but sometimes much longer.

Fruit: Achene. White-stemmed: 4-8 mm long including stout beak, ridged on the back. Richardson's: 2.5-4 cm long, including 0.5-1 mm long beak, usually not ridged.

Root: Fibrous, from stout rhizomes. Rhizomes of white-stemmed pondweed are brown-spotted, with numerous air cavities.

Propagation: Seeds, rhizomes. White-stemmed: forms winter buds.

Importance of plant: Both provide good food and habitat for aquatic animals and waterfowl.

Distribution: Widespread in North America. 

Habitat: White-stemmed: deep, clear lakes, in up to 6 m of water. Richardson's: shallow to deep (0.5-3.5 m) water, often in alkaline lakes and marl encrusted.

May be confused with: Each other. White-stemmed pondweed has longer leaves with hooded tips and its strongly zigzag stem is also diagnostic. Other pondweeds with broad underwater leaves have floating leaves and the leaf bases of submersed leaves do not clasp the stem. Pondweeds often form hybrids, so plants with intermediate characteristics are common. 

Photographs: Closeup of Potamogeton praelongus leaves, Closeup of Potamogeton richardsonii leaves and seedheads

Line Drawings: None available


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