Rough bedstraw

This mysterious-looking shadowy plant is rough bedstraw.  Its leaves grow radially at regular intervals along the branch, and in rough bedstraw each bunch has more or less six leaves in it - this plant has relatives which look very similar, but have fewer or more leaves per bunch.  It also has a relative called fragrant bedstraw which is quite similar but doesn't have a hairy/prickly texture.  This guy prickled the strap on my camera so I am pretty sure it's the rough variety.

you can kinda see the prickles

The tiny white four-petaled flowers are currently giving way to a multitude of small spherical burrs.

Growing in a large mat on the higher, west-side path at about 120th street in Morningside Park, Manhattan.

Yellow sweet clover

Yellow sweet clover.  This is a big, beautiful plant with lots of spikes of yellow flowers and little three-part leaves.  It looks like it could be a cultivated flower.

Growing in an empty lot in Harlem.

Shepherd's purse

Shepherd's purse: it has tiny little white flowers which are barely noticeable.  The heart-shaped seed pods are the more prominent part, and at the base of the plant is a little rosette of toothed leaves.  Those leaves are apparently edible. 

Growing by the sidewalk in an empty lot in Harlem.

Field mustard

Field mustard.  This pretty relative of the cultivated mustards is actually edible, too, and is sometimes sold at the greenmarket.

Growing near the 72nd Street entrance on the west side of Central Park.

Trumpet honeysuckle

Trumpet honeysuckle.  These bizarre, almost tropical-looking bunches of flowers grow on a climbing vine.

Growing up a bush near a stone arch in the middle of the Ramble, Central Park.

Canada violet

Canada violet - a white type of violet, with just a few purple streaks on the bottom petal. 

Deep in the woods of the Ramble, Central Park.

Foamflower

Foamflower.  Lots of wildflower names are appropriate, but this one seems especially so.  Up close, it looks more like a weird undersea creature than a flower.

From further away, it looks more like its namesake:

Growing near the north entrance to the Ramble, Central Park.