It is some kind of moss, obviously. A proper identification is really impossible, since a lot of the traded Bucephalandra are wild-collected or off-cuts from those. Such plants often carry strange things....... different mosses being the most common (and least problematic, compared to ex. vira or nematodes.......).
If the Bucephalandra originates from someones tank, you could ask which mosses are growing in there and google images that look right.