Illustration of <i>Asclepias speciosa</i>
USDA Natural Resources Conservation Service.
1913
<a rel="nofollow" class="external text" href="https://plants.usda.gov/java/largeImage?imageID=assp_001_avd.tif">USDA-NRCS PLANTS Database / USDA NRCS</a>. Britton, N.L., and A. Brown. <i>An illustrated flora of the northern United States, Canada and the British Possessions.</i>