What happens to the fern prothallus after a new sporophyte forms?

After a new sporophyte is formed through fertilization, the prothallium (or gametophyte) serves as a temporary source of nourishment for the developing embryo. The young sporophyte remains attached to the prothallium, absorbing nutrients via a specialized organ called a foot.123

Once the sporophyte develops sufficiently to establish an independent existence—specifically when its root has penetrated the soil and it can sustain itself—the prothallium is no longer needed. In the majority of fern species, the prothallium then shrivels, withers, and dies.23