Image Do I have a weed mixed in with my young fern

The subject is not the young (several weeks old) frond of an interrupted fern on the right which is a bit out of focus, but the in-focus small plant with the half dozen leaves just to the left of center of the picture. The gametophytes are in there as well, all out of focus. I have a dozen peat pots of the ferns going under a dome and a few show growths like the plant left-of-center. I suspect a weed that will compete with the fern. Is it likely to be from the potting soil I used? Any knowledge will be appreciated.