Species: Potamogeton robbinsii Oakes

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Potamogeton robbinsii Oakes

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TAXONOMY

Family:

Potamogetonaceae

Genus:

Potamogeton

Species Synonyms:

none

Common Names:

Robbins’s pondweed
flat-leaf pondweed
fern pondweed

DISTRIBUTION

Canada:

southwestern British Columbia, central Alberta, north – east-central Saskatchewan, southeastern Manitoba – western Ontario – Quebec – New Brunswick – Nova Scotia

Saskatchewan:

north – east-central Saskatchewan; Cluff Lake - Lac la Ronge – Prince Albert National Park – Porcupine Hills

Ecoregion:

Mid-Boreal Upland, Mid-Boreal Lowland, Churchill River Upland

HABITAT

Saskatchewan:

shallow water of quiet lakes and ponds

Associated Species:

Myriophyllum spicatum, Nuphar variegatum, Potamogeton pusillus, Potamogeton zosteriformis, Ranunculus aquatilis

RARITY STATUS

Provincial Status According
to Harms (2003):

Endangered

Nature Conservancy Status:

G5 S2

Saskatchewan Species at
Risk Status:

None

COSEWIC Status:

None

Potamogeton robbinsii is threatened because it is rare or uncommon in Saskatchewan. It is usually locally numerous within limited areas. No threats are known or anticipated for this species.

SPECIES DESCRIPTION

Height:

to 100 cm

Roots:

roots fibrous; rhizomes present

Stems:

branched, terete, stout, without spots, eglandular; turions absent

Leaves:

submersed, crowded, distichous, sessile, 2 – 7 cm long, 3 – 4 mm wide, linear to lanceolate, base rounded and lobed, stiff, lacunae absent, dark green to reddish-green, veins 20 – 60, margin spinulose to serrulate; stipules adnate to the base of the blade, connate, greenish brown to white, fibrous, shredding at tip

Inflorescence:

spikes uniform, moniliform, 7 – 20 mm long, often in branched clusters 3 – 5 cm long, axillary, erect, cylindrical

Flowers:

small, greenish; tepals 4; stamens 4; carpels 4

Fruits:

drupe stipulate, brown, keeled, beak erect


POTAMOGETON KEY FOR SPECIES FOUND IN SASKATCHEWAN

1 Stipular sheaths of submersed leaves adnate to base of leaf blade; leaf margins cartilaginous	P. robbinsii
1 Stipular sheaths of submersed leaves free from base of leaf blade; leaf margins not cartilaginous	2

2 Submersed leaves oblong to lanceolate to nearly orbicular	3
2 Submersed leaves ribbon-like or thread-like	9

3 Leaf margins conspicuously serrate and undulate; turions present	P. crispus
3 Leaf margins entire or undulate; turions absent	4

4 Submersed leaves clasping; floating leaves absent	5
4 Submersed leaves not clasping, may be petiolate; floating leaves present or absent	6

5 Stipules persistent; rhizome with rusty spots	P. praelongus
5 Stipules shredding into fibres; rhizome not obviously spotted	P. richardsonii

6 Floating leaf blade rounded to cordate; stem rusty or black-spotted; submersed leaves arcuate	P. amplifolius
6 Floating leaf blade cuneate or rounded; stems without spots; submersed leaves not arcuate	7

7 Submersed leaves petiolate	P. nodosus
7 Submersed leaves sessile	8

8 Fruits plump, pedicellate; submersed leaf blade 7 – 9-veined	P. alpinus
8 Fruits compressed, sessile; submersed leaf blade 3 – 19-veined	P. gramineus

9 Floating leaves present on at least some plants in a population
9 Floating leaves absent

10 Lacunae present and prominent; submersed leaves with distinction between blade and petiole; leaves dimorphic, the floating ones long-petioled and wider than the submersed ones	P. epihydrus
10 Lacunae absent or not prominent; submersed leaves phyllodial; leaves uniform, no distinction between the floating and submersed leaves	P. natans

11 Nodes without glands	12
11 Nodes glandular	13

12 Leaves 15 – 35-veined, greater than 2 mm wide; stem wing-flattened	P. zosteriformis
12 Leaves 3 – 5-veined, less than 2 mm wide; stem not wing-flattened	P. foliosus ssp. foliosus

13 Stipules fibrous, whitish	14
13 Stipules not fibrous, green, brown or whitish	15

14 Leaf apex acute to apiculate, leaves thin, 5 – 7-nerved; peduncles at most 5 cm long	P. friesii
14 Leaf apex bristle-tipped; leaves firm, 3-nerved; peduncles to 9 cm long	P. strictifolius

15 Fruits 2.5 – 3.5 mm long	P. obtusifolius
15 Fruits 1.5 – 2 mm long	16

16 Mature fruits obovoid; peduncles 1 – 3 per plant; leaf blade with less than 2 rows of lacunae along midrib	P. pusillus ssp. pusillus
16 Mature fruits widest at the middle; peduncles more than 3 per plant; leaf blade with 1 – 5 rows of lacunae along midrib	P. pusillus ssp. tenuissimus