The most common milkweed, Asclepias Syriaca. It's food for monarchs -- I always let them alone & even transplant a couple to around the house. Ones near the house I pinch the very top off so they don't get so tall/leggy and get blown over (they'll sprout new shoots from the leaf-bases). The flowers have a faint but pleasant odor.

https://en.wikipedia.org/wiki/Asclepias_syriaca

Edit: Below is one out my door that the top has been pinched off -- note the leaf-base sprouts coming out. You get more flower heads that way too.

I'll have to think about keeping them. They are in my tulip bed so not really welcome there. I may consider transplanting them. Thank you both.

Tulips are very temporary. A 'tulip bed' is only a tulip bed for a few weeks a year. If there's nothing else in the bed it'll look empty. Even if you remove the milkweed, you'll need something else there.

My tulip bed is not empty. It contains lots of poppies (no roots to compete), ladies mantle in front (hides dying tulip foliage), Huskers Red, and tall plumes of New England asters which bloom later in the fall so I think I am OK in that regard. I just wonder about their root systems, and whether they are invasive. I'll do some research before taking action, but I am taking care of a few health problems at the moment. Thanks for your input.

A. syriaca (and incarnata) are native in Canada. (If your user name is indicating you're in Ontaio.)

A. s. is very difficult to remove. It has a deep and running root system. I have always left plenty but the monarch cats ignore it now, preferring A. tuberosa and especially A. incarnata.