These are propagules of Titanotrichum oldhamii, a rhizomatous gesneriad that is hardy in the Washington, DC area. These propagules can form on the flower spikes: although they are not seed, they can be sown like seed. T. oldhamii can also be propagated from cuttings or rhizomes.
This is what the flower looks like:
And it can be seen here in DCTropic's garden next to (and slightly above) the hosta:
(The pots on the steps are Seemannia.) T. oldhamii is hardy in the Washington, DC area, and does well in moist shade in the ground.
