Weeds in Italy versus weeds in Maryland. The ones with little white flowers look the same to me. (4/18/10: Hairy Bittercress)

Cardamine hirsuta.

Still a mystery. Looks like its name should have "cress" in it.

I think this is the same plant that I noticed last spring. Right here.
[4/19/10: Hairy bittercress (Cardamine hirsuta)]

??? It's kind of viney.

Yarrow? Yes, says Michelle. Achillea millefolium.

Could be lady's thumb, or Pennsylvania smartweed, or tufted knotweed. Anyone know for sure?

???

4/12/11: Turkish speedwell (thanks andrea, see comments). A delicate and hardy little groundcover.

Veronica liwanenis

See also September 23. Looks like, but isn't, rosemary. Even has the same tiny flowers. Has great fall color. [8-13: might be bog-rosemary per Andrea]

Jerusalem artichoke?

Most people, including me, wouldn't call these weeds. But they come up every year in the park next door and I've never been sure what they are. Deer don't eat them so I'd like to borrow a few plants for my yard in the hope they'll spread.

???

Spotted in my friend Shannon's front yard.

Yes, nutsedge. Specifically yellow nutsedge.

Cyperus esculentus.

It looks like wild rosemary but is there such a plant? [8-13: Andrea says Andromeda polifolia or bog-rosemary so we're going with that for now.]

??? Shepherd's purse maybe?

??? (10/6: could this be nutsedge???)

12/26/09 update: Aporn says this is an obedient plant.

Physostegia virginiana.

Sowthistle (Sonchus arvensis). [5/24/10 update]

???

???? Boneset maybe?

And this is ...?? (9/18: Possibly white wood aster.)

Eurybia divaricata.
This is what I'm calling it until someone corrects me.

Now that this weed has finally bloomed I should be able to identify it. (Clammy Ground Cherry, 9/23.)

Physalis heterophylla. (Yes, Michelle, it is a nightshade.)

What IS this stuff? St. John's Wort, I do believe.

Hypericum perforatum.

???

Spotted spurge (Euphorbia maculata).

Some call this a weed. I call it salad. Purslane.

Portulaca oleracea.

A big climbing weed called, some say, Trumpet Vine. It likes to climb up the downspout and onto the roof. But it's never bloomed...

Campsis radicans is the Latin name for trumpet vine. I'm not totally sure that this is the correct ID. More research is called for.

This stuff is everywhere. It's called dock, says gaiagardener. Rumex obtusifolius.

Is this what everyone calls crabgrass? I'm guessing that Lori KP (see comments) is right: it's goosegrass (Eleusine indica).

This plant is close to 4 ft tall. No sign of a flower. I so want to hack it down. But I want to see if it blooms. (7/8: Dug it up. I'll never know.)

(9/26/09 update: Eastern redbud seedling)

I still have no idea what this is. It's not a tomato. Looks like a gigantic marigold without the flowers.