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fern pondweed, potamot de Robbins, Robbin's pondweed

long-stalk pondweed, potamot à longs pédoncules, white-stalk pondweed, white-stem pondweed

Cauline stems

terete, without spots, to 100 cm;

glands absent.

terete, without spots, to 210 cm;

nodal glands absent.

Turions

absent.

absent.

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, conspicuous, convolute, free from blade, white to green, not ligulate, 3–8.1 cm, fibrous, shredding at apex;

blade pale green, rarely olive green, linear-lanceolate, not arcuate, 0.8–2.8 cm × 11–46 mm, base clasping, without basal lobes, margins entire, rarely crispate, apex hoodlike, splitting when pressed, obtuse, lacunae absent;

veins 11–33.

Inflorescences

often branched;

peduncles not dimorphic, axillary, erect, cylindric, 3–5(–7) cm;

spikes not dimorphic, moniliform (i.e., beaded), 7–20 mm.

emersed, unbranched;

peduncles not dimorphic, terminal or axillary, erect to spreading, cylindric, 9.5–53 cm;

spikes not dimorphic, cylindric, 34–75 mm.

Fruits

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, greenish brown, obovoid, turgid, abaxially keeled, occasionally laterally keeled, 4–5.7 × 3.2–4 mm, lateral keels when present without points;

beak erect, 0.6–1 mm;

sides without basal tubercles;

embryo with 1 full spiral.

Rhizome(s)

present.

present.

2n

= 52.

= 52.

Potamogeton robbinsii

Potamogeton praelongus

Phenology Flowering late summer–early fall. Flowering summer–fall.
Habitat Shallow to deep water of ponds, lakes, and slow-flowing rivers Neutral to alkaline waters of lakes, rivers, and streams
Elevation 0–3000 m (0–9800 ft) Greenland; 100–3000 m (Greenland; 300–9800 ft)
Distribution
from FNA
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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[BONAP county map]
from FNA
AK; CA; CO; CT; IA; ID; IN; MA; ME; MI; MN; MT; NE; NH; NJ; NY; OR; PA; SD; UT; VT; WI; WY; AB; BC; MB; NB; NF; NS; NT; NU; ON; PE; QC; SK; YT; Mexico; Greenland; Eurasia
[WildflowerSearch map]
[BONAP county map]
Discussion

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 praelongus is one of the easiest pondweeds to identify with its submersed leaves only clasping the more or less zigzagged stem. The persistent, hugelarge, white stipules provide another clue to this species.

Four hybrids, Potamogeton perfoliatus × P. praelongus (= P. × cognatus Ascherson & Graebner), P. alpinus × P. praelongus (= P. × griffithii A. Bennett), P. crispus × P. praelongus (= P. × undulatus Wolfgang ex Schultes & Schultes f.), and P. gramineus × P. praelongus (= P. × vilnensis Galinus), have been described.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Source FNA vol. 22. FNA vol. 22.
Parent taxa Potamogetonaceae > Potamogeton Potamogetonaceae > Potamogeton
Sibling taxa
P. alpinus, P. amplifolius, P. bicupulatus, P. clystocarpus, P. confervoides, P. crispus, P. diversifolius, P. epihydrus, P. floridanus, P. foliosus, P. friesii, P. gramineus, P. groenlandicus, P. hillii, P. illinoensis, P. natans, P. nodosus, P. oakesianus, P. oblongus, P. obtusifolius, P. ogdenii, P. perfoliatus, P. praelongus, P. pulcher, P. pusillus, P. richardsonii, P. spirillus, P. strictifolius, P. subsibiricus, P. tennesseensis, P. vaseyi, P. zosteriformis
P. alpinus, P. amplifolius, P. bicupulatus, P. clystocarpus, P. confervoides, P. crispus, P. diversifolius, P. epihydrus, P. floridanus, P. foliosus, P. friesii, P. gramineus, P. groenlandicus, P. hillii, P. illinoensis, P. natans, P. nodosus, P. oakesianus, P. oblongus, P. obtusifolius, P. ogdenii, P. perfoliatus, P. pulcher, P. pusillus, P. richardsonii, P. robbinsii, P. spirillus, P. strictifolius, P. subsibiricus, P. tennesseensis, P. vaseyi, P. zosteriformis
Name authority Oakes: Magazine of horticulture, botany and all useful discoveries and improvements in rural affairs 7: 180. (1841) Wulfen: Arch. Bot. (Leipzig) 3: 331. (1805)
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