Milkweed is the common name for the flowering plants in the genus Asclepias.
Common milkweed (Asclepias syriaca), Bluffer’s Park Marina.
Various milkweed species are common all over North America. Milkweed flowers are an important nectar source for various native insects.
Milkweed plans are serve as hosts for the caterpillars of the monarch butterflies. Planting milkweed in your garden is a good way to encourage butterflies and other insects to show up.
For some time milkweed was declared a “noxious weed” and people tried to eradicate it but now they have started to realize that by eradicating milkweed they also kill the insects feeding on it, thereby reducing biodiversity. In particular the drastic reduction of the number of the monarch butterflies got people thinking that it is not very productive to try to preserve a species while trying to eliminate its food source at the same time. So now people seem to be encouraged to leave milkweed plants alone or even plant them in their gardens.
Swamp milkweed (Asclepias incarnata), Milliken Park.
The milky liquid inside the plant contains a highly poisonous cardiac glycoside. Many insects, including monarch butterfly larvae, feast on milkweed and they appear to be immune to the poison. But the poison can accumulate in the insects, this is why monarch butterflies are poisonous.
Further Readings:
Asclepias syriaca on Wikipedia.
Asclepias incarnata on Wikipedia.
Common Milkweed (Asclepias syriaca) on Ontario Wildflowers.
Plant milkweed and save the monarch butterflies Toronto Star.
Ministry OKs monarch-friendly milkweed The London Free Press.
Ontario Weeds: Common milkweed.
Help save the monarch butterflies by planting milkweed.