Potamogeton robbinsii
Potamogeton pulcher
fern pondweed, potamot de Robbins, Robbin's pondweed
heartleaf pondweed, potamot gracieux, spotted pondweed
present.
present.
terete, without spots, to 100 cm;
glands absent.
terete, conspicuously spotted, 8–95 cm;
nodal glands absent.
absent.
absent.
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.
both submersed and floating, ± spirally arranged.
petioles continuous in color to apex, 1–16.5 cm;
blade adaxially light to dark green, lanceolate to round-ovate, 2.5–8.5 cm × 11–44 mm, base rounded to cordate, apex acute to rounded;
veins 15–21.
petiolate, lax;
stipules deliquescent, inconspicuous, convolute, free from blade, light to dark brown, not ligulate, 0.7–1.2 cm, not fibrous, not shredding at tip, apex obtuse;
petioles 0.5–4.5 cm;
blade dark green, linear-lanceolate to lanceolate, often arcuate, 3.5–13.8 cm × 60–165 mm acute, base acute to rounded, without basal lobes, margins entire, crispate, apex not hoodlike, acute to obtuse, lacunae in 2–5 rows each side of midrib;
veins 7–19.
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 axillary, erect to ascending, cylindric, 3.3–9.4 cm;
spikes not dimorphic, cylindric, 17–36 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, dark green to dark brown, ovoid to obovoid, turgid, abaxially keeled, laterally ridged, 5–6.5 × 4.1–5 mm, lateral ridges without points;
beak erect, 0.5 mm;
embryo with 1 full spiral.
apparently unknown not available.
= 52.
Potamogeton robbinsii
Potamogeton pulcher
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.)
Potamogeton pulcher is similar in morphology to P. amplifolius and occurs in similar habitats. Potamogeton pulcher differs from P. amplifolius by the former having lanceolate to linear-lanceolate submersed leaves with fewer than 19 veins, whereas the latter has ovate submersed leaves with more than 19 veins.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
- Local floras:
BC, 
CA, 
OR, 
WA - Local Web sites: CalFlora, CalPhotos,
Flora NW, 
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IL Wildflowers, 
MI Flora, 
MN Wildflowers, 
PNW Herbaria 
WildflowerSearch
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USDA Plants Database- LBJ Wildflower Center
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