It definitely looks like part of the plant but if it is covered in a jelly like substance I am guessing it is molding for some reason. Is there a way to very gently wipe the substance off the plant part? Or take just a little bit of Hydrogen Peroxide 3% no more than 3ml per 10g of tank water, turn off your filters, the slowly squirt the fungus (which would work even better if you could wipe off some of the stuff), and let it sit 20 minutes before turning the filters back on. Then wait and see if the H2O2 kills the substance.