I don't think Blyxa japonica will grow emersed. Mine don't propagate with runners, they kinda just grow another plant connected at the base and you pull it loose and plant it. If you look real close at the base, do the leaves all originate from a crown, or do they all appear to grown off of a short stem? With the blyxa, they will all grow out from a short stem. I believe it is actually classified as a stem plant also.