1 is a Cirsium possibly c. arvense.

Could you show the entire plant 2. Coreopsis sp???

Same with 3. Foliage would help. Dill???

4 looks like a tree seedling.

Possibly a Violet

You never said where you were located. Location does matter.

Your 4th pic reminds me of Ailanthus (Tree of Heaven/HELL). Squeeze a leaf, if it smells of peanut, it is said tree.

#1. Could be Cirsium altissimum, the native Tall Thistle. Look at the leaf underside, and it's white it's likely Cirsium altissimum.

Thanks everyone. I'll add clearer pix shortly. And...I'm in NYC zone 6b.

2 is bolted parsley. 4 is Ailanthus altissima 5 is a Viola species

The Viola looks like the Common Blue Violet in your area, but I'm not 100% sure. If the flower color/shape doesnt match, submit it again. The plant in photo#2 looks like something in Apiaceae. Can you photograph it from further away and put something next to it to show scale.

Number 3 isn't identifiable without foliage, all Apiaceae plants have similar looking umbels and the photo is blurry. Tall Thistle wouldn't be prickly at all and the prickles along the leaf margins, should bend and not poke your fingers when you touch them, and again the leaf undersides would be white.

Ailanthus altissima (the tree that grows in Brooklyn) is definitely an invasive, and a host plant for the spotted lanternfly. So, a weed in my book!

Nos two and three are the same plant, ie bolted parsley, which is Apiaceae.

41North said (and others here also confirmed): "Your 4th pic reminds me of Ailanthus (Tree of Heaven/HELL). Squeeze a leaf, if it smells of peanut, it is said tree."

Bingo! Indeed smells like peanut. ;-) So that seedling has since been pulled up! Thanks.

As for # 5 being a viola species, now that I think about it, that sounds right. For me, it's a keeper then. (I don't have to worry so much about invasiveness, as all my plants are in pots ;-)

Not all Violas are created equal. Viola comprises both pansies and violets. Some people don't like wild violets in their gardens as they spread vigorously, while others tolerate them.

...So the only one that's still not clear is photo #1. Some thought it might be "Cirsium altissimum, the native Tall Thistle"....however, the underside is NOT white...and as mentioned, it DOES have sharp prickles all along the leaf edges (they don't 'bend'...they are hard and sharp...)

I've included a photo of the underside...

Still hoping someone can ID this last plant? Thanks!

I had suggested Cirsium arvense.

Ah thanks peren.all.... maybe I missed that, as many other folks suggested it might be Cirsium altissimum (which it apparently is NOT, as the leaf undersides are not white). So yeah, you very well may be correct! ;-)

I see some things online that suggest it's from Canada, but other sites that say it's also common in the US....that it's invasive... I wonder, so long as I keep it in a POT, should it be ok, or might it self-sow (and then spread elsewhere, potentially causing a problem for other gardens in my immediate area)? I know that invasive, non-native species are bad....

The thistle could be Bull Thistle, Cirsium vulgare. Bull Thistle and Canada Thistle are from Europe.

Thanks Carolb... we have since figured out here, all the other plants. ;-)

The last plant is definitely a Viola species. Bull thistles can grow to the size of automobiles, and their thorns are wicked.

As long as you do not let it go to seed it should be fine. It probably won't flower as it is restricted by the pot and very young. I dig them out but it makes me a little sad because the finches love the seeds.