Fern Life Cycle Labeled – Spore to Prothallus to Fern

All 15 stages and parts on the diagram

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Spore to prothallus 8

Fern (sporophyte) The leafy plant you see. It makes the spores.
Sorus A cluster of spore cases under a leaf.
Sporangium A stalked case in which the spores form.
Annulus A row of thick-walled cells on the spore case.
Meiosis The cell division that makes the spores.
Spores Tiny single cells that drift away. Each can grow into a prothallus.
Germinating spore A spore that has started to grow.
Prothallus (gametophyte) The small heart-shaped plant. It makes the sperm and the eggs.

Sperm and egg 7

Antheridium The male organ of the prothallus. It makes the sperm.
Sperm The male cells of the fern. They swim through water to the egg.
Archegonium The female organ of the prothallus. It holds one egg.
Egg The female cell, in the base of the archegonium.
Fertilization A sperm joins the egg. The result is the zygote.
Zygote The fertilized egg, a single cell. It grows into the new fern.
Young fern (new sporophyte) The new plant, the next sporophyte. It grows out of the prothallus.

How this list was compiled: Every name was checked on 2026-10-03 against sources read that day; a name is kept only when two of them use it. (1) C. Stuart Gager, Fundamentals of Botany, 1916 (public domain), the life history of a fern, https://archive.org/details/fundamentalsofbo00gagerich : the spore-case with a clearly differentiated region, the annulus, of thick-walled cells; the spore puts out a germ-tube and a first rhizoid, and this is germination; a tiny flat green body, often heart-shaped, the prothallus; archegonia near the notch and antheridia among the rhizoids; the neck of the archegonium projects and the venter with the egg is sunk in the tissue; the fusion of sperm and egg is fertilization, and free water is required for the sperms to reach the egg; the fertilized egg is diploid; the young embryo. (2) National Council of Educational Research and Training (India), Biology, textbook for class 11, chapter 3, Plant Kingdom, section 3.3, read on archive.org, https://archive.org/details/kebo103 : the main plant body is a sporophyte; the sporangia produce spores by meiosis; the spores germinate to give gametophytes called prothallus; antheridia and archegonia; water is required for the male gametes to reach the archegonium; fusion with the egg forms the zygote, which produces the sporophyte. (3) U.S. Forest Service, Fern Reproduction, https://www.fs.usda.gov/wildflowers/beauty/ferns/reproduction.shtml : a diploid sporophyte generation and a haploid gametophyte generation; the plants we see as ferns are the sporophyte; the mature gametophyte looks like a little flat green heart; sperm swim through a film of water to fertilize the egg; the first tiny leaf of the sporophyte emerges from the gametophyte. (4) American Fern Society, About Ferns, https://www.amerfernsoc.org/about-ferns : a mature sporophyte makes haploid spores by meiosis; they germinate into gametophytes; antheridia and archegonia; the sperm are motile; sporangia in clusters called sori. (5) Wikipedia, Fern, Sorus, Annulus (botany), Prothallus and Alternation of generations, https://en.wikipedia.org/wiki/Fern : a sorus is a cluster of sporangia; the annulus is an arc or ring of specialized cells on the sporangium; the prothallus is anchored by rhizoids; the zygote develops into a diploid sporophyte. Licence: own work

The drawing: Drawn for this site on 2026-10-03 from plain curves; own work, nothing traced. Licence: own work

How it works

A fern life cycle diagram labeled in two steps. First the fern sheds spores, and one grows into a small heart-shaped prothallus. Then a sperm reaches an egg on the prothallus, and a new fern grows from it.

Read the full guide

Two plants take turns

The fern you see is the sporophyte. Under its leaves, sori hold the sporangia, where meiosis makes haploid spores. A spore grows into the prothallus, a separate little plant that is the gametophyte.

Sperm, egg and a new fern

The prothallus carries antheridia and archegonia. Sperm swim through a film of water to an egg. Fertilization gives a diploid zygote, and the zygote grows into a young fern.

A fern makes no flowers and no seeds. It spreads by spores.

Questions and answers

What are the stages of the fern life cycle?

The fern plant, its sori and sporangia, the spores, the prothallus, sperm and egg, the zygote, the young fern, and the grown fern again. The fern is the sporophyte and the prothallus is the gametophyte.

What is a prothallus?

The gametophyte of a fern: a tiny, flat, green plant, often heart-shaped, that grows from a spore. It lives on its own, held down by rhizoids, and carries the antheridia and the archegonia.

Where does meiosis happen in a fern?

In the sporangia, the small spore cases that sit in clusters called sori on the underside of the leaves. Meiosis there makes the haploid spores.

Why do ferns need water to reproduce?

The sperm have to swim from an antheridium to the egg in an archegonium. Fertilization can happen only when a film of water covers the prothallus.

Is the fern plant a sporophyte or a gametophyte?

A sporophyte. The plant with fronds is the diploid generation, and it makes the spores. The gametophyte is the small prothallus, which is easy to miss.