These are growing in a quart jar terrarium on a spongy mass that appears to have once been wood or bark. I'm uncertain where that material came from but the jar did once host moss taken from a coastal forest in northern CA. I started this particular jar approximately five years ago with substrate taken from a hill and riverbed in southern CA. Following a period of neglect (very little, if any light) I added a small patch of what appears to be a club moss and a leaf (taken from my backyard in southeast NE) and, of course, mail-ordered springtails.
I have additional specimens in a larger jar with a similar history, although in that case they are growing directly on the substrate, which is store-bought soil for acid-loving plants.
The plants appear to be new since the latest additions, but the wood seems rotted enough to have been in the jar since the beginning.
My apologies for the blurry photo. I included it for a better view of the root-like structures, which have a yellow-ish color (something that doesn't come across well in the pictures).