Sphagnum Hitchhiker

[Tschimm]

Some months ago I had some Chilean Sphagnum left from a repotting and put it in a little pot to use it later.
Someday a little plant begun to grow and grow and grow.
Today, the terete leafs are more than a foot long and the pot is full of roots.
Leafs are hollow like chives.
The seeds must have been in the moss. It's very unlikely that the seeds came from anywhere else.
Does anybody has an idea what it could be ?