Species: Myriophyllum alterniflorum DC.

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Myriophyllum alterniflorum DC.

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TAXONOMY

Family:

Haloragaceae

Genus:

Myriophyllum

Species Synonyms:

Myriophyllum alterniflorum var. americanum Pugsley

Common Names:

alternate-flowered watermilfoil

DISTRIBUTION

Canada:

northwestern Mackenzie District, northern Saskatchewan – Manitoba – Ontario – New Brunswick – Newfoundland – Nova Scotia

Saskatchewan:

northern Saskatchewan; Lake Athabasca – Porcupine Hills

Ecoregion:

Mid-Boreal Upland, Churchill River Upland, Athabasca Plain, Tazin Lake Upland

HABITAT

Saskatchewan:

shallow lakes

Associated Species:

spike watermilfoil, yellow pond lily

RARITY STATUS

Provincial Status According
to Harms (2003):

Threatened

Nature Conservancy Status:

G5 S1

Saskatchewan Species at
Risk Status:

None

COSEWIC Status:

None

Alternate-flowered watermilfoil is vulnerable because it is rare or uncommon in Saskatchewan. No immediate threats are known for this species.

SPECIES DESCRIPTION

Height:

fibrous

Stems:

aquatic, slender, 15 – 20 cm long, whitened on drying

Leaves:

underwater leaves whorled, 0.5 – 1 cm long, with up to 7 pairs of divisions; above water leaves greatly reduced

Inflorescence:

spikes above water, 2 – 5 cm long, 1 – 3-flowered, male flowers solitary or in opposite pairs, female flowers whorled at the base of the spike; bracts alternate, upper often entire, lower comb-like or pinnately lobed

Flowers:

flowers unisexual; sepals 3 – 4, petals 0 or 4; stamens 8; ovary inferior, carpels with reddish bumps

Fruits:

nut-like, deeply 4-lobed

MYRIOPHYLLUM KEY FOR SPECIES FOUND IN SASKATCHEWAN

1 Flowers in axils of leaves below or above water; stamens 4	M. pinnatum
1 Flowers in a terminal spike; stamens 8	2

2 Floral bracts alternate; under water leaves with up to 7 pairs of thread-like divisions	M. alterniflorum
2 Floral bracts opposite or whorled; under water leaves with up to 11 pairs of thread-like divisions	3

3 Above water leaves reduced, bract-like, upper leaves entire, lower saw-toothed; leaf whorls greater than or equal to 1 cm apart	M. sibiricum
3 Above water leaves pinnately lobed, margins comb-like, saw-toothed or entire; leaf whorls less than 1 cm apart	4

4 Floral bracts shorter than or equal to fruits, margin saw-toothed to entire	M. verticillatum
4 Floral bracts usually surpassing the fruits, margin saw-toothed to comb-like	M. spicatum