We found this wonderful blog that explains about it.
There are over 100 native species of Milkweed (Asclepias) in North America. The best choice for Milkweed you can make is to pick species for your butterfly garden that are native to your local area. The Monarchs have thousands of years of interaction with these plants and are well adapted to them. Locally native species die back each winter, only to grow again each spring.
When you add lots of locally native species of Asclepias to your butterfly garden, you are helping to make a difference for Monarch Butterflies and to preserve the amazing phenomenon of Monarch Migration. So please learn more about which Milkweeds are the most important for your garden ~Carole Sevilla BrownPlease visit Native Plants and Wildlife Gardens to read more.