Hi --
Your seedlings look like the ones from my Money plant (Lunaria biennis). It blooms in the spring with the tulips, with a purple/magenta stalk of flowers.
Then the flowers very reliably turn into flat green seedpods that have the brown papery exterior and the seeds and the shiny section inside. The plant is called "lunaria" because the shiny parts resemble the moon ("luna" in Latin).
If well-spaced out and in the sun where they can grow straight and tall, your stems with the seed pods can be harvested in the Fall and make lovely arrangements. If they, like mine, are a bit crowded, and I don't get to harvesting them in time, the stems get brittle and break, and the plant reseeds profusely, Mine has gotten a bit out of hand, but it is not hard to weed them out...
They are a biennial, so you should have nicely established small plants from your seedlings this year that will bloom next spring ( with the late daffodils)... Then they will die off and you need to allow it to seed each year if you want it to keep being there... That hasn't been a problem for me :-) ...
I like it because it is a herbaceous plant that blooms in the early spring with the bulbs. I have some white narcissus and pink tulips near mine and they looked nice together this year.
I haven't tried sending a photo before, but I am sending one to show you the seedlings as they come up "volunteer" in my garden -- below the yellow daffodils are small seedlings -- they are from the previous Fall's seed... To the right of of the daffodils, in front of that piece of wood, are a couple pyramidal-shaped plants -- those are the 1-year old lunaria seedlings that were already setting flower buds at that time. They were blooming by the time the late narcissus and the midseason tulips were blooming...
