Photosynthetic haploid gametophytes evolve from the germinating spore. The gametophyte is generally amorphous to heart-shaped with root-like rhizoids projecting downward to anchor the plant. Also located ventrally are male antheridia within which sperm develop and mature, and female archegonia within which eggs develop and mature.
Rain induces swelling in the antheridia, causing them to burst and release multiflagellated sperm that are transported via water droplets to the egg.
Fertilization results in a diploid zygote that matures into an adult sporophyte consisting of a rosette of leafy fronds. This is the plant one usually recognizes as a fern.
Sori develop on the ventral portion of pinnae (leaflets), and within these sporangia form, completing the alternation of generations.
|This is a fern gametophyte. Notice how small this plant is - barely half a centimeter long. This is the most vulnerable stage in the life cycle of the fern - the gametophytes are prone to dessication, trampling, being eaten, and being out shaded by the surrounding foliage. Additionally, when the young sporophyte emerges, it is essentially a parasite on the gametophyte until it can grow its first leaf. The gametophyte must nurture the young sporophyte until it grows large enough to produce its own food.|