Okay, I got it. Draw your simple strokes of grass with the taper brush (if you want it to be this simple). Group the lines. Convert to line shape and then create your brush. Add some randomness and you get some nice cartoon grass. I am not sure if this was how it was done for this illustration(I'm sure it wasn't), but it gets some decent cartoon grass. I can better illustrate if you want. Hope this helps somebody.