Compass Plant, perhaps. Silphium laciniatum.

tj

Lactuca serriola

Lactuca and Convolvulus. Just pull them: it won’t take half an hour.

It could be Calystegia sepium, and not Convolvulus arvensis.

That looks similar to what grows all over my lot, getting 10 ft high or more end of season. It has watery, hollow stems, milky sap & smells like lettuce. I also have Lactuca serriola which is kinda similar but not IMO what the OP is showing.

Ok, floral, you’re right. The Convolvulus/Calystegia will take quite a bit more effort to eradicate than the Lactuca. A first round assault will help.

Ben, I ran through all possible species of Lactuca, and serriola look the closest. What species do you think it is?

I do know about the convolvulus, unfortunately! Not sure about the weed with the small white sort-of-daisy-ish flowers, which I've seen in fields all my life but don't know what it is.

I think I will have to get back over there and take a closer look at the main stems to know if it is Lactuca serriola or Silphium laciniatum, will I not? They seem to be very similar as far as the leaves. Unless one of you can see the stem well enough to tell? Aren't silphium stems very hairy, while Lactuca are not?

It is not Silphium lacinatum. I’ve grown that and it starts life with a huge basal rossete of lacinate foliage that yours is missing. in addition, Silphium stems are solide and Lactuca are hollow.

Silphium laciniatum leaves don't have spines running down the midvein of the adaxial surface. Their leaves usually never grow more than 3 feet high, before they send up a flower stalk. Silphium leaves are thick and leathery, and would never wilt and look limp like yours. Silphium leaves don't bleed white sap. It's definitely a question of which Lactuca species it is, so we have to wait. A photo of your Lactuca would be nice Ben.

Too bad it isn't Silphium, since it is critically endangered here - although it sounds impossible to transplant, and I really couldn't leave it to grow.

Lactuca serriola, absolutely, cannot be anything but. Ben, perhaps your 'serriola' is another species?

Yeah, Silphium have huge taproots that are some of the deepest in the meadow ecosystem, if I recall. They're easy enough from see tho.

Ben, your Lactuca looks pretty close to the OP's plant. Check and see if it has pickles running along the midvein on the underside of the leaf. There is a lot of variation in serriola leaves. Sometimes they aren't lobed at all, and sometimes they are heavily lobed. The lobes of Lactuca serriola stick out straight or point down, whereas the lobes of Silphium laciniata point up.

Jay, the example in the pic I show above does NOT have prickles. The typical serriola that also grow all around does have the prickles, tho they're not hard & won't really stab you. Also, the serriola get only 3 -4 ft tall, where what I showed above grows WAY taller. Typical serriola below w/reddish stems.

Now, pic on the fly that's not the best, but another (small) ex of what I showed originally. Hollow, watery green stem.

Just for fun, here's a 6 ft tall jewelweed beside my house from last summer. There's a spouting there that watered it well.

I agree on Calystegia. I was using ”convolvulus” carelessly. I’ve fought it for 30 years.

Floral, all the Calystegia species have been moved to Convolvulus, so you were correct. I knew about a couple of them, but had no idea they all were reassigned.

Ben, I'm not very good at identifying Lactuca species because they all look so similar. A couple candidates are L. canadensis and L. floridana which both have hollow stems, but it can possibly be a different species. Let us know what color the flower is, either blue or yellow. It night help narrow it down. Thank you for supplying the photos!

Jay, I'm certainly not good at IDing these various lettuces. A search shows canadensis and floridana both have reddish young stems like serriola, so not them. I do know that the first pic I showed originally gets the little yellow flowers and then the wind-blown seeds, which seed like crazy. L. serriola also has the tiny yellow flowers.