Identifying Milkweed

[texas butterfly]

Since there are so many varieties of milkweed, how would one confirm a plant was in the milkweed family?

My guess would be you could tear a leave and if it has white substance this would be a milkweed.

But, is this a good scientific way of determining a plant is milkweed.

Maybe not all milkweed have the white substance?

Thanks,

[Mona Miller]

http://www.monarchwatch.org/milkweed/index.htm
Monarch Watch -- Milkweed
http://www.monarchwatch.org/milkweed/guide/index.htm
Photos of Milkweed from Monarch Watch

http://countrynaturals.com/Butterfly-Moth/milkweed3.htm
There are more plants that have the white sap, including dogbane.

http://asclepias.homestead.com/
Some photos of Texas milkweeds

viewtopic.php?f=7&t=1483#p6955
Growing and Identifying milkweed.