OregonFlora: Potamogeton alpinus vs. Potamogetonaceae

	Potamogeton alpinus	Potamogetonaceae
	northern pondweed, reddish pondweed	pondweed family
Habit		Herbs perennial or rarely annual, rhizomatous or not; turions sometimes present.
Stems	terete; to 200 cm; nodal glands absent.
Leaves	submersed and floating or submersed only.	alternate or nearly opposite, submersed or both submersed and floating, petiolate or sessile; stipules well developed, sometimes connate and sheathing, sometimes fused to the leaf; if fused to the leaf then often ligulate (extending beyond the base of the blade as a ligule).
Floating leaves	elliptic or oblanceolate to obovate or oblonglinear, 40–70(100) × 10–25(40)mm; reddish green; base gradually tapering to petiole; tip obtuse or acute; veins (7)9–13(15); petioles 0–12 mm.
Submersed leaves	sessile, attached to stem nodes, not attached to stipules; stipules (12)15–25(40)mm; tip blunt; blades oblong-linear to linear-lanceolate, 45–180(250) × 5–20 mm; base rounded to cuneate; margins entire; tip obtuse or acute; lacunae in 0–6 rows on each side of midvein; veins 7–9.
Inflorescences	emersed; spikes cylindric, 10–35 mm; peduncles terminal or axillary; erect, 30– 100(160)mm.	terminal or axillary spikes, cylindric or capitate, rarely paniculate, pedunculate; bracts 0.
Flowers		bisexual; tepals 4 in 1 series; stamens (2)4, attached to the petals; in 1 series; anthers distinct, dehiscing longitudinally; pistils 1 or 4, sessile or rarely short-stipitate.
Fruits	pedicellate, obovoid; turgid; (2.5)3–3.5 × (1.7)2–2.4 mm, dorsally keeled, laterally keeled or not; beaks dorsally curved, 0.5–0.9 mm.	drupaceous, 1-seeded.

	Potamogeton alpinus	Potamogetonaceae
Distribution	[WildflowerSearch map] [BONAP county map]	[BONAP county map]
Discussion	Ponds, lakes, and slow-moving streams. 1200–2200m. BR, BW, Casc. CA, ID, NV, WA; north to British Columbia, east to Greenland; Eurasia. Native. Potamogeton alpinus is often red when fresh. This species hybridizes with P. nodosus, P. gramineus, and P. praelongus.	Cosmopolitan in fresh water (rarely brackish) habitats. 3 genera; 2 genera treated in Flora. Leaves of Potamogetonaceae species are stipular. The submersed leaves are attached to stem nodes or to the stipules. If the leaves are attached to the stipules, they appear to have a ligule above the point of attachment. Reproductive features are important in separating taxa. We strongly recommend that no one collect specimens of Potamogetonaceae that are lacking reproductive structures. North American pondweeds have often been classifed in a single genus, Potamogeton in the broad sense. However, the genus includes two lineages that we recognize at the generic level, Potamogeton in the strict sense and Stuckenia. In Stuckenia, leaf blades are attached to most of the stipule, diverging from it in the upper third, whereas in Potamogeton, blades are free from stipules or attached only in the lower fourth. Submersed leaves of Stuckenia are opaque, channeled, and turgid, whereas those of Potamogeton are translucent, flat, and without grooves or channels.
Source	Flora of Oregon, volume 1, page 496 Nick Otting, Richard Brainerd, Barbara Wilson	Flora of Oregon, volume 1, page 494
Sibling taxa	P. amplifolius, P. berchtoldii, P. crispus, P. diversifolius, P. epihydrus, P. fibrillosus, P. foliosus, P. gramineus, P. illinoensis, P. natans, P. nodosus, P. praelongus, P. pusillus, P. richardsonii, P. robbinsii, P. zosteriformis
Synonyms	Potamogeton alpinus ssp. tenuifolius, Potamogeton alpinus var. subellipticus, Potamogeton alpinus var. tenuifolius
Web links	Local floras: BC, CA, OR, WA Local Web sites: CalFlora, CalPhotos, Flora NW, PNW Herbaria WildflowerSearch iNaturalist (observations) USDA Plants Database LBJ Wildflower Center SEINet Plants of the World Online Encyclopedia of Life Wikipedia Google Image Search	Local floras: CA, OR Local Web sites: CalFlora, CalPhotos, Flora NW, PNW Herbaria WildflowerSearch iNaturalist (observations) LBJ Wildflower Center SEINet Plants of the World Online Encyclopedia of Life Wikipedia Google Image Search

Potamogetonaceae

northern pondweed, reddish pondweed

pondweed family

Habit

Herbs perennial or rarely annual, rhizomatous or not; turions sometimes present.

Stems

terete; to 200 cm; nodal glands absent.

Leaves

submersed and floating or submersed only.

alternate or nearly opposite, submersed or both submersed and floating, petiolate or sessile;

stipules well developed, sometimes connate and sheathing, sometimes fused to the leaf; if fused to the leaf then often ligulate (extending beyond the base of the blade as a ligule).

Floating leaves

elliptic or oblanceolate to obovate or oblonglinear, 40–70(100) × 10–25(40)mm; reddish green;

base gradually tapering to petiole;

tip obtuse or acute;

veins (7)9–13(15);

petioles 0–12 mm.

Submersed leaves

sessile, attached to stem nodes, not attached to stipules;

stipules (12)15–25(40)mm;

tip blunt;

blades oblong-linear to linear-lanceolate, 45–180(250) × 5–20 mm;

base rounded to cuneate;

margins entire;

tip obtuse or acute; lacunae in 0–6 rows on each side of midvein;

veins 7–9.

Inflorescences

emersed;

spikes cylindric, 10–35 mm;

peduncles terminal or axillary; erect, 30– 100(160)mm.

terminal or axillary spikes, cylindric or capitate, rarely paniculate, pedunculate;

bracts 0.

Flowers

bisexual;

tepals 4 in 1 series;

stamens (2)4, attached to the petals; in 1 series;

anthers distinct, dehiscing longitudinally;

pistils 1 or 4, sessile or rarely short-stipitate.

Fruits

pedicellate, obovoid; turgid; (2.5)3–3.5 × (1.7)2–2.4 mm, dorsally keeled, laterally keeled or not;

beaks dorsally curved, 0.5–0.9 mm.

drupaceous, 1-seeded.

Potamogetonaceae

Distribution

[WildflowerSearch map]

[BONAP county map]

Discussion

Ponds, lakes, and slow-moving streams. 1200–2200m. BR, BW, Casc. CA, ID, NV, WA; north to British Columbia, east to Greenland; Eurasia. Native.

Potamogeton alpinus is often red when fresh. This species hybridizes with P. nodosus, P. gramineus, and P. praelongus.

Cosmopolitan in fresh water (rarely brackish) habitats. 3 genera; 2 genera treated in Flora.

Leaves of Potamogetonaceae species are stipular. The submersed leaves are attached to stem nodes or to the stipules. If the leaves are attached to the stipules, they appear to have a ligule above the point of attachment. Reproductive features are important in separating taxa. We strongly recommend that no one collect specimens of Potamogetonaceae that are lacking reproductive structures. North American pondweeds have often been classifed in a single genus, Potamogeton in the broad sense. However, the genus includes two lineages that we recognize at the generic level, Potamogeton in the strict sense and Stuckenia. In Stuckenia, leaf blades are attached to most of the stipule, diverging from it in the upper third, whereas in Potamogeton, blades are free from stipules or attached only in the lower fourth. Submersed leaves of Stuckenia are opaque, channeled, and turgid, whereas those of Potamogeton are translucent, flat, and without grooves or channels.

Source

Flora of Oregon, volume 1, page 496
Nick Otting, Richard Brainerd, Barbara Wilson

Flora of Oregon, volume 1, page 494

Sibling taxa