Why can one horsetail gametophyte support more than one young sporophyte?

In the life cycle of horsetails (Equisetum), a single gametophyte can support more than one young sporophyte because it acts as a source of nourishment for the developing embryos.1

After fertilization occurs within the archegonium, the resulting zygote develops into an embryo. This young sporophyte remains attached to and is sustained by the gametophyte until it is capable of developing its own independent shoot and root systems. Because the gametophyte is capable of producing multiple archegonia, it can support the simultaneous development of two or more of these young sporophytes before the gametophyte eventually dies and decays.12