Asclepias erosa

(A.leucophylla, A.l. var.obtusa, A.erosa var. obtusa, A.obtusata, A.Rothrockii) Asclepias erosa is a desert milkweed. It has some of the most beautiful silver foliage with hints of purple in the veins. Plant in full sun. Plant with Opuntia basilaris. California milkweeds go dormant in fall triggering Monarch Butterflies to migrate south on schedule. This means the plant will look great in spring, half eaten and mangy in fall, then it goes dormant completely. (If you order these during their dormancy period they ship very well but will arrive as a bag of soil with some roots in it.) Milkweeds are among the most important insect plants. Butterflies and some beetles use milkweeds as nectar sources and the foliage as food.
The alkaloids associated with this milkweed and other milkweeds give the monarch and other butterflies that feed on it protection from predators. Alkaloids from the wrong milkweed (South American, Mexican, etc.) can expose the butterflies to predation. If the monarch or other butterfly has not evolved with the milkweed they may have limited tolerance for the particular alkaloid or latex of the plant species. The California flyway runs from Baja to Canada, it does not include Mexico proper nor Central America. If you live in Chicago you can plant Mexican species (Asclepias mexicana) or Asclepias tuberosa, don't plant our species. You might look at the Monarch entry in James Scott's Butterflies of North America and articles by Fink, L and L.P. Brower.
I would guess the symptoms to be similar to the problem of intolerance to legumes that some people have. Which milkweed is best for me?