My daughter and I are working on a layout and she wants to create a pond with cattails. I had no idea how to make them, but thanks to the internet, I was able to find some people who do and luckily, shared how they did it!
I tried this one and it worked pretty well. Unfortunately, I can't find my "proof of concept" cattail, so I can't show a picture to you. It uses small gauge electrical wire with the insulation stripped except for the top. This creates the bulge that is the characteristic feature on a cattail. Read the top post at the following link and you'll see what I mean: http://cs.trains.com/mrr/f/88/t/209737.aspx
I also found this great video by Kathy Millatt that demonstrates a slightly different method. She uses small gauge electrical wire as well and then applies several layers of white glue to the top to create the bulge. You can check it out on this video: https://youtu.be/P0L7qItLPHk.