It's gooseneck loosestrife.
This is mixed news.
On the one hand, gooseneck loosestrife doesn't have anything like the horrors of its purple cousin. It's an ornamental, people plant it deliberately. My patch was certainly planted deliberately, in this awful section of drainage bed where nothing wants to grow. It grows like iron in the horrible clay soil we've got here, it'll survive shade and wet and abuse, and it has neat flowers, which bees mostly like.
On the other hand, it spreads. Not like death and plague and wildfire, like the purple loosestrife, but it's definitely invasive. I have read anecdotes of it battling mint and winning. Everything I've read says that it must be controlled with an iron fist. On the other hand, it is reported to live happily with Joe Pye weed and daylilies, which ironically is what it's living with right now.
The upshot of all of it is that I'm leaving it in the bed where it is now, because A) not much grows there and B) I wouldn't be able to get rid of it anyway. The advice for getting rid of the stuff all seems to end with "...and then get a priest and sow the fields with salt." However, I must exercise diligence. If it creeps and crawls and lounges out of the bed, it must be ripped up and excised and eradicated. Fortunately, it pulls easy. Unfortunately, if there is a molecule of root stock remaining, it'll come back.
My desire to plant it in among the English Ivy in hopes that it will destroy the ivyish foe is unworthy, and probably unrealistic. But I do so hate English Ivy, and we're so over-run in much of the wooded area that it'd take a flamethrower and a bulldozer to get it all out. If only we had a powerfully invasive native plant that could meet the ivy on its own terms...
Also, there's a tiny blue morning glory blooming in my bed. It's very cute. I didn't plant it, and it's barely knee-high to a grasshopper. I quite like morning glory, but I like it under control, and I know wild morning glory is writhing and vicious weed, so it's on notice. Stay cute and contained, and it may live. Cross me, and it's war.
All my dreams of the peaceful, Zen, one-with-natureness of gardening have largely been shattered by now. Instead, I find that gardening is like being El Presidente of a sulky and dissatisfied nation made up of thousands of seperate ethnic groups, many of whom are mortal enemies. No peaceful coexistance for plants. I find myself crowding them into terra cotta prisons, setting up botanical reservations, savagely beating anybody who slinks out of line. "Tear down this railroad tie!" cry the plants, crowding at the edge of their bed. Instead, I send in the army. (Okay, James.) There are beheadings. The weed whacker is used with a cruel and indiscriminate hand. The injured plants crowd back in the bed, lick their wounds, gaze at me with intense dislike. "The butterfly weed isn't even USING this space!" the ground ivy grumbles, as I rip it out. "Why can't I?" "It's not yours," says El Presidente. "To the gulag with you!" "Jerk," say the plants.
"We've been here for generations!" they cry, as I tear out swaths of plants and shove in natives I think ought to live there, recreating a sort of vegetative Palestinian/Israeli conflict in the bed. The parallels are undeniable. Suddenly I find myself thinking of the British settlement of Israel, not just as an interesting idea done badly, with no long-term planning, but as an exercise in gardening guilt. There is nothing I could have done to stop trillium from becoming endangered, I wasn't even born yet, and yet I will rip out ivy that's existed in this spot for fifty years to try and restore the abused trillium, and run roughshod over the ivy that tries to intrude. Does the ivy resent my interference? It has every right to. But what else can you do?
Gardening and politics take place in an imperfect world, and we do both badly. I cannot blame the ivy for being resentful, or the trillium for wanting to live, but now I can't even blame the gardener for making the whole mess in the first place. The garden has pretty much eradicated my ability to blame anybody. We're living in a muddled world. Planting loosestrife probably seemed like a great idea at the time. Maybe it still will be. I don't know.
El Presidente wishes the plants would live together in peace, but they probably won't. But eh, we muddle through.