Reminds me of balsam...

Thanks...I just looked up balsam, but all the images I'm seeing seem to show serrated edges on the leaves, which my plant does not have...

What is the geographic location? Did this plant volunteer in the pot, or did you plant seeds for something in it?

It's on an NYC rooftop...I think we are Zone 6B. It's possible that at one point I'd planted something and then didn't make note of it, because (at the time) it seemed it didn't 'take'. I think at one time over the past few months, I'd tried Black-Eyed Susan, and Milkweed. But I'm guessing it's some type of a volunteer...

Leaf arrangement seems opposite? Is it? If this is a milkweed, it will bleed white latex if you tear a leaf.

I’m seeing alternate. The plant behind is opposite.

Perhaps Oenothera biennis? Can't think of anything else.

Oh my goodness... while I'd not torn a leaf yet (as was suggested by someone, above), to see if it bleeds white (possibly milkweed...), today I was looking at the plant again and...I'm seeing the beginning of flower buds....and then I thought, 'Wait a MINUTE!...it couldn't be...COULD it??' The beginning, very pale green buds look VERY similar to my Great Blue Lobelia buds (on my balcony, a floor below the rooftop). And so I tore off on of the leaves and compared it to my lobelia, and yup, the leaves seems similar.

The growth pattern of the leaves up and down the stem also mimic my Great Blue Lobelia...it's just that...the plant up on my rooftop appears to be about 6 weeks or so (development wise) behind the GBL plant on my balcony (and only has one stalk, vs my established balcony plant, that has a few dozen stalks).

COULD this be it? Does GBL self-sow...or maybe a bee or bird helped facilitate this? ;-)

Yes, Lobelia siphilitica self seeds freely. They can bloom in the first year too. They aren't long lived, so I allow seedlings, so I always have some in the garden. I think the curled leaves threw everyone off. Good thing that you waited.

These are all self seeded.

Hooray. Thanks for the confirmation! I'm thrilled that I'll have another pollinator on my rooftop. A friend also recently gave me some zinnia seeds....I'd never grown zinnia before....but I now understand they are pretty hardy and easy to grow. And indeed, I didn't have to do much...I just pressed the seeds into the soil...kept the soil watered and...within about 3-4 weeks I had very strong plants. I think every single seed germinated.... and I can now see the beginnings of one flower...I suspect it will be fully open within the week. ;-)

Lynn Nevins. Zinnia can handle some cool weather, but they are annuals. Here in Illinois if I want more of them for next year, I collect the seeds and plant them in the spring, otherwise, they don't have a bunch of seedlings if Iet them drop their seeds. Perhaps the freezing winter kills the seeds. Other annuals will self seed prolifically on their own, like Verbena bonariensis, and Salvia coccinea.

There is also a white version of Lobelia siphilitica. Alba. Bees and other pollinators will flock to the white flowered variety also.

Thanks. Yes, I did see that Zinnia are annuals, but I also seem to recall reading that because they self-sow quite well, that they end up resurfacing every year... so sorta a perennial? ;-)