You don't mention where you live, so that makes an answer more difficult. You're sure it isn't Cannabis? I lived in Minnesota for years and "Minnesota Green" was fairly common. Even though it had very little THC the state considered it a noxious weed and land owners were required to eradicate it.

You also mentioned Hibiscus, which would have been my second guess, but you apparently don't believe it's this either. (I have a swamp Hibiscus which leaves very much resemble Cannabis).

Horse Chestnut seedlings? False Aralia? A photo would be very helpful...

Mike

Cleome aka Spider Flower has foliage that smells and looks strikingly like like marijuana. It is a self-seeding annual.

jenny

Could it be Lupine?

See here:

http://www.desertusa.com/mag99/mar/papr/deslupine.html

There are different types of Lupine and one very pretty version is sold at chain nursuries. They do self seed. Are you getting these in your lawn or are they coming up in your garden only?

My neighbors are always joking about my Lupine really being 'something else'.

Do a search on "lupine" and you will find pics of the vairous types. I bet that is what it is.

I for got to mention that Lupine does not bloom flowers the first year so all you will see are the marijuana looking leaves. You may not be able to ID it by the flowers because there won't be any.

Here is a link with a better pic of the leaves close up and shows how pretty the flowers are:

http://www.wiseacre-gardens.com/plants/perennial/lupine.html

I have not found it to be invasive (Z5) and it is easy to pull out if it pops up where you don't want it. Once it becomes 'established' it is harder to get rid of.