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
Associated species: Artemisia ludoviciana ssp. ludoviciana, Juniperus horizontalis, Pascopyrum smithii, Schizachyrium scoparium var. scoparium
Provincial Status According
to Harms (2003):
Nature Conservancy Status:
G5 S1
Saskatchewan Species at
Risk Status:
Asclepias verticillata is endangered in Saskatchewan because it is extremely rare in the province. In addition to this species being locally sparse, there are only two known populations in Saskatchewan. Threats facing A. verticillata 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 A. verticillata 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: Buchloe dactyloides and 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: taproots thin, secondary roots many
Stems: perennial, tufted, thin, to 0.5 cm wide glabrous, milky latex
Leaves: whorled (3-6), sessile, linear, 3-7 cm long, 1-2 mm wide, abaxial surface lightly tomentulose especially along margin, midrib prominent and white, adaxial surface glabrous, margin revolute
Inflorescence: umbels several, axillary or terminal, 8 – 10-flowered; involucre small; pedicels tomentulose
Flowers: 5-merous; calyx greenish, reflexed at maturity; corolla yellowish, reflexed at maturity; corona hood white, alternate to corolla lobes, broadly ovate, barely equalling anthers; horn falcate, incurved, protruding from corona hood; gynostegium (adnation of the anthers and the stigma) present; ovary apocarpous but adnate with the style and stigma
Fruits: follicles erect, up to 12 cm long, without protuberances; seeds numerous, flattened, silky-comose
1 Horn
1 No horn
A. viridiflora
2 Leaves linear, in whorls
A. verticillata
2 Leaves wider, opposite
3 Leaves ovate or lanceolate, 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