Potamogeton friesii |
Potamogeton robbinsii |
|
---|---|---|
flat-stalk pondweed, Fries' pondweed, potamot de Fries |
fern pondweed, potamot de Robbins, Robbin's pondweed |
|
Rhizomes | absent. |
present. |
Cauline stems | compressed, without spots, 10–135 cm; glands green, greenish brown, or gold, to 0.7 mm diam. |
terete, without spots, to 100 cm; glands absent. |
Turions | terminal or lateral, common, 1.5–5 cm × 1.5–4 mm, soft; leaves ± 4-ranked; outer leaves 2–3 per side, base corrugate, apex apiculate to acute; inner leaves reduced, arranged into fan-shaped structure and oriented at 90° angles to outer leaves. |
absent. |
Leaves | submersed, ± spirally arranged, delicate to rigid, sessile; stipules not persistent, inconspicuous, convolute, free from blade, white, not ligulate, 0.55–2.1 cm, fibrous, coarse, shredding at tip, apex obtuse; blade light green, rarely olive-green to.somewhat reddish, linear, not arcuate, 2.3–6.5 cm × 1.2–3.2 mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, acute to apiculate, lacunae absent or 1 narrow row each side of midrib; veins 5–7(–9). |
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 or axillary, erect or rarely recurved, slightly clavate, 1.2–4.1(–7) cm; spike not dimorphic, cylindric, 7–16 mm. |
often branched; peduncles not dimorphic, axillary, erect, cylindric, 3–5(–7) cm; spikes not dimorphic, moniliform (i.e., beaded), 7–20 mm. |
Fruits | sessile, olive-green to brown, obovoid, turgid, not abaxially or laterally keeled, 1.8–2.5 × 1.2–2 mm; beak erect, 0.3–0.7 mm; sides without basal tubercles; embryo with 1 full spiral. |
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 friesii |
Potamogeton robbinsii |
|
Phenology | Flowering and fruiting summer–fall. | Flowering late summer–early fall. |
Habitat | Calcareous to brackish waters of lakes and slow-flowing streams | Shallow to deep water of ponds, lakes, and slow-flowing rivers |
Elevation | 0–3100 m (0–10200 ft) | 0–3000 m (0–9800 ft) |
Distribution |
AK; CO; CT; IA; ID; IL; IN; MA; ME; MI; MN; MT; ND; NE; NH; NY; OH; PA; RI; SD; UT; VT; WA; WI; WY; AB; BC; MB; NB; NF; NS; NT; ON; PE; QC; SK; YT; Eurasia
|
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
|
Discussion | Potamogeton friesii is a fairly common linear-leaved species, especially of calcareous waters of lakes and streams of the upper Midwest. Whenever turions are present, the species is easily identified, as it is the only one with the outer leaves of the turions having corrugate bases and the inner leaves turned at right angles to the outer leaves. Two hybrids, Potamogeton friesii × P. pusillus (= P. × pusilliformis Fischer [P. × intermedius Fischer]) and P. friesii × P. obtusifolius (= P. × semifructus A. Bennett ex Ascherson & Graebner), have been described. (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 | Potamogetonaceae > Potamogeton | Potamogetonaceae > Potamogeton |
Sibling taxa | ||
Name authority | Ruprecht: Hist. Stirp. Fl. Petrop. 43. (1845) | Oakes: Magazine of horticulture, botany and all useful discoveries and improvements in rural affairs 7: 180. (1841) |
Web links |
|