How does a spore develop into a fern gametophyte?

The development of a fern gametophyte begins when a spore lands in a suitable, moist environment and its wall cracks, initiating germination.123

Upon germination, two structures emerge from the spore:
* A nongreen rhizoid, which anchors the developing plant to its substrate.23
* A green mother cell, which serves as the foundation for the rest of the gametophyte.2

Initially, the gametophyte typically grows as a single filament of cells. Under optimal lighting, this structure expands into a two-dimensional, heart-shaped sheet of cells known as a prothallium, which is generally one cell layer thick except at its center. Growth is driven by an apical cell that is eventually replaced by a meristem located in an apical notch.243

Once mature, the prothallium produces male and female sex organs to facilitate fertilization, after which the gametophyte typically withers as the new sporophyte becomes independent.143