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Prairie milkweed produces one and a half to two inch balls of 30-100 greenish-white flowers in the axils of a few of the mid-stem and upper leaves; the flowers are supported on 1/2"-3/4" pedicels. Each flower is about 1/8" across and 1/4" long; the flowers are a variation on the typical (complex) milkweed morphology with 5 sepals, a 5-lobed corolla with 5 petals (often with purple blotches at their tips) that are reflected backwards to cover the top of the pedicel, 5 hoods without horns, and a short central column that rises above the hoods; there is a distinct gap between the bases of the petals and the crown. Seedpods are 4-5" long with a fat base (attached to the pedicel) tapering rapidly to a narrow tip. Prairie milkweed can be confused with whorled milkweed (Asclepias verticillata) — both occur in Jackson Park — but whorled milkweed has even narrower (grass-like) leaves than prairie milkweed, is a shorter plant, and has pure white flower that do bear horns.

Asclepias

Asclepias hirtella

prairie milkweed [Blooms: Jun-Aug]

Whorled milkweed's flowers are white, occurring in small (1-3") clusters that rise from leaf axils. Individual flowers are typical milkweeds (except for their color), 1/4" across; horns are sickle-shaped, petals are white or greenish-white. Once you recognize that this plant IS a milkweed, given its grass-like leaves in whorls, it is impossible to mistake it for any other local species.

Asclepias

Asclepias verticillata

whorled milkweed [Blooms: Jul-Sep]