Potamogeton robbinsii
Potamogeton crispus
fern pondweed, potamot de Robbins, Robbin's pondweed
crisp-leaf pondweed, crispate leaf pondweed, curled pondweed, curly pondweed, curly-leaf pondweed, potamot crepu
present.
absent.
terete, without spots, to 100 cm;
glands absent.
flattened, without spots, to 100 cm;
nodal glands absent.
absent.
common, axillary or terminal, 1.5–3 × ca. 2 cm, hard;
leaves ± 2-ranked;
outer leaves 1–4 per side, base not corrugate, apex rounded;
inner leaves rolled into linear, terete structure, oriented parallel to outer leaves.
submersed, conspicuously 2-ranked, sessile, stiffish;
stipules persistent, conspicuous, adnate to base of blade about ± ¼ length of stipule, connate, greenish brown to white, ligulate, 0.5–2 cm, fibrous, shredding at tip, apex obtuse;
blade dark green to reddish green, linear to lanceolate, not arcuate, 2–7(–12) cm × 3–4(–8) mm, base rounded, with basal lobes, not clasping, margins minutely spinulose to serrulate, not crispate, apex not hoodlike, acute, lacunae absent;
veins 20–60, fine.
submersed, ± spirally arranged, sessile, lax;
stipules persistent to deliquescent, inconspicuous, convolute, free from blade, brownish, not ligulate, to 0.5 cm, not fibrous, not shredding at tip, apex obtuse;
blade light to dark green, linear, not arcuate, 1.2–9 cm × 4–10 mm, base obtuse to rounded, without basal lobes, not clasping to nearly clasping, margins conspicuously serrate, not crispate, apex not hoodlike, round to round-acute, lacunae in 2–5 rows each side of midrib;
veins 3–5.
often branched;
peduncles not dimorphic, axillary, erect, cylindric, 3–5(–7) cm;
spikes not dimorphic, moniliform (i.e., beaded), 7–20 mm.
unbranched, emersed;
peduncles not dimorphic, terminal or rarely axillary, erect to ascending, cylindric, 2.5–4 cm;
spikes not dimorphic, cylindric, 10–15 mm.
stipitate, brown, obliquely obovoid, turgid, abaxially and laterally keeled, 3–4(–5) × 2(–3.3) mm, lateral keels without points;
beak erect, recurved at apex, 0.7–0.9 mm;
sides without basal tubercles;
embryo with less than 1 full spiral.
sessile, red to reddish brown, obovoid, turgid to slightly concave, not abaxially or laterally keeled, 6 × 2.5 mm;
beak apically recurved, 2–3 mm;
sides without basal tubercles;
embryo with 1 full spiral.
= 52.
= 52 (Europe).
Potamogeton robbinsii
Potamogeton crispus
Potamogeton robbinsii is our most easily recognized species when it is fertile. It is the only species with branched inflorescences. The species, however, occurs in fairly deep water, forming large colonies that essentially cover the substrate. Only rarely do the plants flower. It also is the only species with truly auriculate leaves, the blades forming small lobes projecting past the stem on each side of the stem. Leaf blades of other Potamogeton species may have slightly rounded bases, but no others have lobes that actually protrude past the stem.
The species has a fairly large disjunction; primarily known from the northern part of the flora, it also occurs in the Tensas River area, Baldwin County, Alabama. The Alabama population has been collected on at least two occasions over 40 years, once as recently as 1970.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
No specimens have been seen from New Brunswick, but the species is to be expected there.
Potamogeton crispus, an introduced species, has spread throughout much of North America. The expansion of this species’s range from its original collection in North America, apparently about 1840, has been discussed (R. L. Stuckey 1979). This is the only species of pondweeds in North America with serrate leaves and consequently it is easily recognized.
Life history of Potamogeton crispus is unusual as it flowers and fruits in late spring and early summer, at which time it also produces turions. The plants decay shortly after those structures develop, leaving only fruits and turions, which survive the summer. No one has observed any seed germination, but the turions (referred to as dormant apices) germinate in late summer or fall, and the plants overwinter as small plants only a few cm centimeters in size, even under the ice in northern climates (R. L. Stuckey et al. 1978). Growth then continues as the water begins warming in the spring.
One hybrid, Potamogeton crispus × P. praelongus (= P. × undulatus Wolfgang ex Schultes & Schultes f.), has been described.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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- Local Web sites: CalFlora, CalPhotos, Flora NW, Go Botany, IL Wildflowers,
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MD Biodiversity, MI Flora, MN Wildflowers, 
MO Plants, PNW Herbaria - WildflowerSearch
- iNaturalist (observations)
- USDA Plants Database
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- Plants of the World Online
- Encyclopedia of Life
- Wikipedia
- Google Image Search
