the grassy part near the tip of the limb is from moss growing on the tip with algae. the rest of the green on the limb is a grassy looking green algae. the big stump on the right side the whole top is completely covered in moss and looks great.
i initially just stuck pieces of moss inbetween cracks and tied it to any pieces using fishing line. Make sure you trim the moss as it grows because it can spread very quickly and vacuum it because it collects alot of small particles of waste etc.
i'll try to a post an updated version on the forum in a day or two. I've since removed the white sucker (went into the pond because it was too big) and i also got rid of the big stump for more swimming room.