Papaver somniferum. A garden escape

It's not native in N. America.

Opium poppy? How interesting. Well, no one is going to get arrested for growing this, as it is out in a wild riparian area. Precisely ONE PLANT. Wonder how it got there. Garden escape? Some neighbor is growing it?? It happens to be in the creek bed below the house of a guy who, when in high school decades ago, was known as the local pot guy. Indeed, it's evidently not native in North America, but is widely distributed here, produces lots of seeds, and can be considered invasive. Maybe we'll see more of them next year.

You'd need to be growing acres of this plant to be of concern to the DEA or other "plant police"! A single poppy is not going to pose any issues :-) These are popular and fast growing ornamental annuals and can be found in gardens and p-patches (PNW equivalent of allotments) all over my area. The seeds are easily come by from any number of seed vendors.

I'd be surprised if it were genuinely invasive, rather than simply naturalised. It will seed around in disturbed soil but I doubt it would oust any native species. At least no more than the human activity which produced the growing conditions it prefers.

As I said, no one is going to be arrested for one poppy in a wild area, but it would be interesting to rummage around in this neighbor's yard, and look for a whole bed of them. In the U.S., under the Controlled Substances Act of 1970, Papaver somniferum is considered a Schedule II substance—putting it into the same category as methadone and fentanyl. The Opium Poppy Control Act of 1942 was repealed in 1970. But if you're growing lots of them to make narcotics, yes, that's still illegal.

The seed came from somewhere. That being the case, such poppy seeds are good food sources for birds, so it could have been carried in from a long ways away. Now, poppies are acknowledged in Texas as being slightly invasive.

Commercial opium is collected from cultivars with far larger, more productive pods and white or pale mauve flowers. These old fashioned cottage garden poppies aren't likely to be a problem. You could call them bread seed poppies if you prefer.

around here (Germany, Switzerland) the Papaver somniferum seems to be forbidden to be traded commercially, so

some creative seed company labeled them something like "handicryft" or "arrangement Poppies"

in our allotment they tend to pop up after you moved or disturbed/ digged the soil