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Key to Asclepias

Apocynaceae

Asclepias

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(c) Fleming, Gary P.
(c) Weakley, Alan
1 Sap clear; leaves alternate; corolla orange to yellow
1 Sap milky (the milkiness often difficult to show in A. verticillata, which has numerous, whorled, linear leaves); leaves either opposite, subopposite, whorled, or alternate (occasional, irregularly alternate leaves present in A. stenophylla and A. engelmanniana, alternate but closely spiraled leaves typical in A. pumila, all of which are distributed west of the Mississippi River and have linear leaves); corolla orange, red, white, cream, green, pink, or purple.
  2 Leaves lanceolate, ovate, or elliptic, 1-5 (-10)× as long as wide.
    3 Leaves with petioles mostly (3-) 4-20 mm long (rarely sessile, and only in the western A. emoryi).