Bracken Ferns are some of the most widespread plants on the planet and have been around for at least 55 million years. They are found on every continent except Antarctica. In some places they are used for food but may contain carcinogens. The brown clusters at the underside edges of this frond, known as sori, are sporangia that produce and contain the fern's reproductive spores. On other ferns in Glacier the sori are frequently grouped in circles rather than around the edges like this.