Biology: alternation of generations: ferns

Tutoring biology, life cycles come up. The tutor mentions a fern one.

Ferns are vascular plants. As is typical with plants, they undergo alternation of generations (see my post here). However, how that works can be surprising for some plants.

With ferns, the plant one sees and calls a fern is diploid (2n). It’s called the sporophyte since it will produce spores. Its sporangia are found on the under-surface of its leaves. Within, meiosis happens, producing spores that are haploid (n). The mature spores are released into the environment; the hope for each spore is that it will find a welcoming environment so it can grow into a gametophyte. Fern gametophytes can be less than a centimetre, so not noticeable. They are haploid, but produce both antheridia (whence sperm are produced) and archegonia (each of which produces an egg) on the same individual. When the environment is wet, the sperm swim from the antheridia to the archegonia, and fertilize the eggs.

Each fertilized egg is a zygote which will start mitosis. At first, it’s dependent on the host gametophyte, but eventually develops into a sporophyte, and the cycle is complete.

Source:

upenn.edu