Potamogeton groenlandicus |
Potamogeton robbinsii |
|
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Greenland pondweed |
fern pondweed, potamot de Robbins, Robbins' pondweed |
|
Rhizomes | absent. |
present. |
Cauline stems | terete, without spots, 20–50 cm; glands white, 0.1–0.7 mm diam. |
terete, without spots, to 100 cm; glands absent. |
Turions | terminal or axillary, common, 4.2–8.4 cm × 1.4–2.5 mm, soft; leaves ± 4-ranked; outer leaves 2 per side, base without corrugations, apex acute to apiculate; inner leaves unmodified. |
absent. |
Leaves | submersed, ± spirally arranged, sessile, delicate; stipules deliquescent to persistent, inconspicuous, convolute, free from blade, brown, not ligulate, 0.45–1.91 cm, not fibrous, not shredding at tip, apex obtuse; blade pale to deep green, linear, not arcuate, 2.6–8.8 cm × 0.7–1.7 mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, acute to apiculate, lacunae absent or present, 0–3 rows each side of midrib; veins 7–11. |
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. |
Inflorescences | unbranched, emersed; peduncles not dimorphic, terminal, erect, cylindric, 20 mm; spikes not dimorphic, cylindric, 5 mm. |
often branched; peduncles not dimorphic, axillary, erect, cylindric, 3–5(–7) cm; spikes not dimorphic, moniliform (i.e., beaded), 7–20 mm. |
Fruits | not laterally keeled, 2.6–2.7 × 2 mm; beak erect, 0.3 mm; sides without basal tubercles; embryo with 1 full coil. |
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. |
2n | = 26. |
= 52. |
Potamogeton groenlandicus |
Potamogeton robbinsii |
|
Phenology | Flowering late summer. | Flowering late summer–early fall. |
Habitat | Ponds and lakes | Shallow to deep water of ponds, lakes, and slow-flowing rivers |
Elevation | 10–450 m (0–1500 ft) | 0–3000 m (0–9800 ft) |
Distribution |
Greenland |
AK; AL; CA; CT; ID; IL; IN; MA; ME; MI; MN; MT; NH; NJ; NY; OH; OR; PA; RI; UT; VT; WA; WI; WY; AB; BC; MB; NB; NS; NT; NU; ON; PE; QC; SK
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Discussion | Of conservation concern. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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.) |
Source | FNA vol. 22. | FNA vol. 22. |
Parent taxa | ||
Sibling taxa | ||
Synonyms | P. pusillus subsp. groenlandicus | |
Name authority | Hagström: Kongl. Svenska Vetenskapsakademiens Handlingar n.s. 55(5): 127. (1916) | Oakes: Magazine of horticulture, botany and all useful discoveries and improvements in rural affairs 7: 180. (1841) |
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