Do they bloom with a yellow head? Sorta look like goldenrod.

Subspecies in development or conditions, perhaps. One of the stinging nettle patches I have is rather narrow leafed like this. It is a moist and rather shady locale. Judging from the top picture, I'm going to guess that location is part sun/part shade? FataMorgana

obviously you need to stop them from setting seeds now, so use your scythe with abandon. Next year consider covering the beds fairly late, after most weeds have sprouted, and plant only transplants in holes through the mulch. I prefer wood chips, because they give you two years of no weeds, and they make a layer of seed-free soil eventually, but black plastic and cardboard will do too. Basically, you will be unable to seed directly for a couple of years or more until weeds can be controlled. This can always be done with relatively little work, so long as you mulch and plant late. I am also in SE MI, and a good time to do this is around June 15. Perennial weeds, you will have to pull by hand.

The leaves on my plant seem to be narrower than on images I see for burnweed on the internet. Also the leaves are soft almost velvety and the stems are whitish covered with soft white fuzz.