Try googling "lemna minor". It's a type of duckweed.

Lemna is a plant floating on water surface.
Jiggreen: the seedling are to young to "have passport", this can be anything. Place current pictures, older plant will be easier to recognise.

It's a daunting process, but you could look through the photo gallery in the link below, and see if you can find your plant.

Here is a link that might be useful: TNC Invasive Species

seedlings are kind of hard to identify, but could it be purslane? I can't remember for sure what it looks like when it is small.

jiggreen,

My best guess is that these are seedlings of some kind of smartweed (Polygonum species). If the newest, youngest leaves are very narrow with their two edges rolled under and if the leaves gradually flatten by way of unrolling of the two edges, then the plant is definitely a smartweed (Polygonum species).

Regards,
Rufino

those seedlings are growing up, and beginning their free-for-all on my garden bed. here is what they look like now...

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and i yanked a couple to bring inside to try to get a better shot. sorry for the blur.

{{gwi:1341750}}

one thing i just realized about this weed is that the undersides of the younger leaves are pinkish, which can be seen in the pictures.

these weeds are getting a lot longer and they almost seem vinelike.

still desperate for help.....

jiggreen

p.s. i looked up polygonum and i don't think that's it. i also started scrolling through that list of invasives and i gave up after the first 40 minutes!