Asclepias verticillata L.
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Family: Asclepiadaceae
Genus: Asclepias
Species Synonyms: none
Common Names: whorled milkweed
eastern whorled milkweed
Canada: southeastern Saskatchewan, southern Manitoba, southwestern Ontario
Saskatchewan: southeastern Saskatchewan; near Estevan
Ecoregion: Moist Mixed Grassland
Saskatchewan: grazed pastures; dry clay or shale soil on south-facing, often eroded, grassland and alkaline coulee slopes
United States: creeping juniper, little bluestem, western wheatgrass, white sagebrush
Provincial Status According
to Harms (2003):
Nature Conservancy Status:
G5 S1
Saskatchewan Species at
Risk Status:
Whorled milkweed is endangered in Saskatchewan because it is extremely rare. In addition to this species being locally sparse, there are only two populations in Saskatchewan. Threats facing whorled milkweed include increased grazing pressure since both populations occur in grazed pastures. In addition, one of the sites is likely to have been affected by the construction of the Rafferty Dam. The last visit to the whorled milkweed populations recorded in the W. P. Fraser Herbarium was in 1997. It should be noted that this species is found within one mile of other provincial rarities: buffalo grass (Buchloe dactyloides) and whorled milkwort (Polygala verticillata) (Harms 1989).
Harms V.L. 1989. Distribution & Status of Provincially Rare Plants in the Souris River Valley, Southeastern Saskatchewan. Fraser Herbarium Technical Report 89-1.
Height: 20 - 50 cm
Roots: taproot thin, secondary roots many
Stem: perennial, tufted, thin, to 0.5 cm wide hairless, milky latex present
Leaves: whorls of 3 – 6, sessile, linear, 3 – 7 cm long, 1 – 2 mm wide, underside lightly woolly especially along margin, midrib prominent and white, upper surface hairless, margin rolled
Inflorescence: umbels several, axillary or terminal, 8 – 10 -flowered; bracts small; flower stalks woolly hairy
Flowers: sepals 5, greenish, reflexed at maturity; petals 5, yellowish, reflexed at maturity; corona hood white, alternate to petals, broadly oval, barely equalling anthers; horn sickle-shaped, incurved, protruding from corona hood; anthers and stigma fused; carpels separate from each other but fused with the style and stigma
Fruits: pods erect, up to 12 cm long, without bumps; seeds numerous, flattened, silky-hairy
1 Horn
1 No horn
A. viridiflora
2 Leaves linear, in whorls
A. verticillata
2 Leaves wider, opposite
3 Leaves oval or lance-shaped, tapering to base; pod without tubercles
A. ovalifolia
3 Leaves oblong or oval, rounded to cordate at base; pods with soft tubercles
4 Hoods 10 - 13 mm long with a dark colored midrib; pod terminus abruptly narrowed to tongue-like terminus, approximately 5 mm long
A. speciosa
4 Hoods 4 - 7 mm long, midrib at most partly dark coloured; terminus not abruptly narrowed, approximately 3 mm long
A. syriaca