Also called/being rebranded butterfly flower. Doug Tallamy is trying to rebrand them monarch's delight.
Part of
milkweed genus Asclepias
(whose ❀ blossom is the ⚘❀ state wildflower of Illinois)
in
dogbane family Apocynaceae.
Native to North America.
Uses by native peoples
(Ethnobotany database)
Asclepias hosts caterpillars of 13 species
of butterflies and moths, in some areas,
including being the only host plant for eggs and larvae of the
monarch butterfly Danaus plexippus.
Poster of monarch butterfly Danaus plexippus lifecycle, larval
host plants, adult nectar plants, and growing info for these plants. 
Growing milkweeds for
monarch butterflies
Milkweed—It's Not
Just for Monarchs
Uses by butterflies,
planting info
Uses by 🐝︎ bees,
planting info
Use in a sidewalk strip garden or mailbox garden, bloom dates, height, light, moisture, etc. (Pennsylvania). (pages 17, 23, 24, 27 and 41)
Wildflowers of West Michigan (page 13)
Bloom dates (Michigan). (page 3)
Bloom dates (NE Illinois). (Wild Ones members only)
Bloom dates and planting info. (page 3) (Wild Ones members only)