Taxonomically, ferns are considered vascular plants but they don’t reproduce like seed-bearing plants. The orange clusters are composed of sori (singular sorus). They contain the sporangium, the reproductive structures of ferns, and are usually found on the underside of the fern leaf. Sori are an important visual clue to fern identification. They can be circular, like Polypodium virginianum (Rock polypody, seen here), or comma shaped. The protective covering of sori, the indusium, is absent in Polypodium. Arrangement along the leaf also matters; rows in this case. In our area, Polypodium grow in places with little or no soil such as rocks, cliffs and outcrops. I found this example on a big rock.