From Flora of Indiana (1940) by Charles C. Deam
In the lake area this milkweed is found in very sandy soil on roadside knolls, in very sandy fallow fields, and in prairie habitats. In the southern part of the state it is found in similar habitats and on the crests of sandstone ridges in open woodland, and very rarely in hard, clay soil. Probably entirely absent from many counties of the Tipton Till Plain.
Simple, erect or sometimes decumbent, 3-8 dm, with 2-5 pairs of lvs and a single (rarely 2) long-peduncled terminal umbel; lvs oval or broadly oblong, 7-15 cm, obtuse or rounded at summit, broadly rounded or commonly cordate at the sessile or subsessile base; peduncle 1-3 dm; umbel large, usually many-fld; cor greenish-purple, its lobes 8-11 mm; hoods pink, 5 mm, about equaling the gynostegium, the lateral margins adjacent, the broad summit truncate, entire or with a few low obtuse lobes; horns subulate, much exsert; fr 10-13 cm, erect on deflexed pedicels. Dry fields, prairies, and open woods, usually in sandy soil; N.H. to se. Minn., s. to Fla., Neb., and Tex. June-Aug. A. ةntermedia Vail is the hybrid with no. 7 [Asclepias syriaca L.].
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
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