Ask Mr. Smarty Plants

Last question first: A weed is a plant that is not where you want it to be. We can probably all agree on some plants, like poison ivy, being a weed. No one wants it anywhere. If milkweed is in a pasture and the farmer doesn't want his stock grazing on it, he sees it as a weed. But you, obviously concerned about the well-being of the Monarch, do not.

When we searched our Native Plant Database on "milkweed;" there were 46 hits, of which 6 of them were plants having "milkweed" in their common names, but were not members of the genus Asclepias, family Asclepiadaceae. One, Asclepias syriaca (common milkweed), was the only one with "common" in its name. However, we are assuming you are referring to the genus Asclepias as a group, all of which do, indeed, support the Monarch butterfly, and allow that butterfly to pass some of the toxins from the milkweed on to its offspring as protection against predators.  There are no doubt some milkweeds that are perhaps not as widespread, and might be considered rare, but by and large, the Monarchs would seem not to be in imminent danger of extinction because of their food source.

However, let's talk a little bit more about what makes a plant considered endangered, rare, threatened, etc.We went to a USDA website for Threatened and Endangered Plants and got a listing of the members of the genus Asclepias that are protected in various states; two are on the Federal threatened list.  

From a U.S Fish and Wildlife Service website Endangered Species Program. we extracted this quotation:

'An “endangered” species is one that is in danger of extinction throughout all or a significant portion of its range. A “threatened” species is one that is likely to become endangered in the foreseeable future.'

The site goes on to tell you far more than you probably ever want to know about getting a plant or animal declared endangered, with many links to other sites for more information. Since you are from Massachusetts, we did a search on our Native Plant Database on the Asclepias genus. From this, we found 10 species of milkweed native to your state and extending west, north and south.

Asclepias native to Massachusetts and their natural range:

Asclepias amplexicaulis (clasping milkweed) - as far west as Kansas and Texas

Asclepias exaltata (poke milkweed) - as far west as Minnesota

Asclepias incarnata (swamp milkweed) - all but West Coast states and Mississippi, plus Manitoba, Ontario and Quebec

Asclepias incarnata ssp. incarnata (swamp milkweed) - all but West Coast states and Arizona, plus Manitoba, Ontario and Quebec

Asclepias purpurascens (purple milkweed) - 31 states and Ontario

Asclepias quadrifolia (fourleaf milkweed) - approx. 27 states and Ontario

Asclepias syriaca (common milkweed) - 40 states and large portion of Canada

Asclepias tuberosa (butterfly milkweed) 43 states and Eastern and Central Canada

Asclepias verticillata (whorled milkweed) - all states as far west as Montana and Arizona, midsection of Canada

If you assess all this information, we believe you'll agree that there is little chance the Asclepias will need to be declared endangered. 

From our Native Plant Image Gallery:

Asclepias amplexicaulis

Asclepias exaltata

Asclepias incarnata

Asclepias purpurascens

Asclepias quadrifolia

Asclepias syriaca

Asclepias tuberosa

Asclepias verticillata