Because we live in the desert of southeast Arizona we have many varieties of cactus plants. The one that is my favorite from a painter's point of view is the Prickly Pear cactus. I like it because of its shapes...roundish paddles that grow in different directions...and colors...everything from green to turquoise to pinks and purples. Here are a couple of pictures ( below) of them at various stages.
The painting itself is done on a surface called Multimedia Artboard. I hadn't used it before this project, and it makes an interesting ground for pastel. It's made from paper and resin and comes in white and black. I used black for mine. It accepts pastel well and leaves an interesting texture which is perfect for THIS subject matter. I did have a hard time making fine detailed marks, but again, for this subject I felt it was alright. This surface is also advertised for oils and acrylics. The website that makes this paper is http://multimediaartboard.com/Home_Page.php You might be interested in experimenting with it sometime.