Ferns are among the oldest plants on land, and they still cover the shaded floor of many forests. They have stems, roots and leaves that carry water. But they never make flowers, and they never make seeds.
Instead, ferns reproduce with spores. Their life cycle uses two separate plants, and one of them is so small that most people never notice it. This guide explains what a fern is, how it lives, and why it matters.
What a Fern Is
Vascular, but Seedless
A fern is a vascular plant. It has tubes that carry water and sugars, the same kind of plumbing that trees and flowers use. That plumbing is what let plants grow tall on dry land.
But a fern is seedless. It has no flowers and no seeds, and it reproduces with spores. Spores are single cells rather than packaged embryos. Ferns belong to a group of seedless vascular plants called the pteridophytes.
Not a Moss, Not a Horsetail
Ferns are easy to confuse with other plants. Mosses are not ferns, because mosses have no water-carrying tubes at all. Horsetails and club mosses do have tubes, but they are separate lineages. They are not ferns either.
| Feature | Fern | Moss | Seed plant |
| Water-carrying tubes | Yes | No | Yes |
| Reproduces by | Spores | Spores | Seeds |
| Flowers | No | No | Usually |
The Parts of a Frond
Fronds, Pinnae and Rachis
A fern leaf is called a frond. Many fronds are divided into smaller leaflets. A major leaflet is a pinna, and a pinna can split again into pinnules. The central stalk that holds the blade is the rachis.
Fronds grow from a rhizome. A rhizome is a stem, often creeping along or under the ground. Roots grow from it too, and they anchor the plant and take in water and minerals.
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| A frond is divided into pinnae, and each pinna can split again. Image: Kingfiser, CC BY-SA 4.0, via Wikimedia Commons |
Sori: The Spore Factories
Look at the underside of a mature frond and you may see rows of small brown dots. These are sori. A sorus is a cluster of sporangia, and each sporangium makes spores.
Some ferns cover each sorus with a small flap called an indusium. Others leave it bare. Either way, sori are a normal part of the plant. They are not a fungus, an infection or a disease, even though they are often mistaken for one.
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| Sori are clusters of sporangia, the structures that make spores. Image: Forest and Kim Starr, CC BY 3.0 US, via Wikimedia Commons |
A Life Cycle in Two Stages
Ferns have a life cycle with two different plants. One makes spores, and the other makes eggs and sperm. The two stages take turns, and they look nothing alike.
The Sporophyte You See
The plant you recognize as a fern is the sporophyte. It carries two sets of chromosomes, so it is diploid. Its sporangia make spores by meiosis, and each spore carries just one set of chromosomes.
The Tiny Gametophyte
A spore can grow into a gametophyte. This stage is small, flat and often heart-shaped. It is called a prothallus, and it carries one set of chromosomes, so it is haploid.
The prothallus makes eggs and sperm. The sperm must swim to an egg through a film of water. That need is why ferns do best in damp places. After fertilization, the zygote grows into a new sporophyte, and the cycle begins again.
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| The gametophyte is a tiny flat plant that makes eggs and sperm. Image: Ilse Anahi Carrasco, CC BY 4.0, via Wikimedia Commons |
Where Ferns Grow
Shade, Moisture and Epiphytes
Most ferns grow in moist, shaded places such as forest floors and ravines. Others grow as epiphytes, perched on tree trunks and branches where they catch rain and fallen leaves. A few ferns even live in water.
Tree Ferns and Aquatic Ferns
Ferns cover a huge range of sizes. Some aquatic ferns have leaves only a few centimeters long. At the other end, tree ferns can reach about 24 meters, close to 80 feet.
Ferns have been on land for a very long time. They appear in the fossil record by the Devonian period, about 420 million years ago. Today there are roughly 10,500 to 12,000 living species.
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| Tree ferns show how tall a seedless vascular plant can grow. Image: P. Hughes, CC BY-SA 4.0, via Wikimedia Commons |
Why Ferns Matter
Ferns do useful work where they grow. Their dense fronds and roots cover soil and shelter small animals in the understory. Some grow high in the canopy as epiphytes.
Ferns also have a deep history. They were among the plants of the ancient swamp forests of the Carboniferous period. Those forests helped form coal, along with other plants such as tree-sized club mosses.
People grow ferns as garden and house plants. A few kinds are eaten, but care matters. Ostrich fern fiddleheads should be identified carefully and boiled well. Bracken, or Pteridium aquilinum, contains toxic compounds and is not a safe food.
One small fern helps farmers. Azolla floats on water and lives with a nitrogen-fixing bacterium. The pair adds nitrogen to rice paddies, so Azolla is used as a natural fertilizer.
Key Terms in Plain English
| Term | What it means here |
| Vascular plant | A plant with tubes that carry water and sugars through the body. |
| Pteridophyte | A seedless vascular plant, such as a fern or a club moss. |
| Spore | A single reproductive cell that can grow into a gametophyte; not a seed. |
| Sporophyte | The diploid stage that makes spores; in ferns, the leafy plant you see. |
| Gametophyte | The haploid stage that makes eggs and sperm. |
| Prothallus | The small, flat gametophyte of a fern. |
| Frond | The leaf of a fern. |
| Rachis | The central stalk of a frond blade. |
| Pinna | A major leaflet of a divided frond. |
| Rhizome | A stem, often underground, from which fronds and roots grow. |
| Sorus | A cluster of sporangia, often seen as a dot under a frond. |
| Indusium | A small flap that covers some sori. |
| Sporangium | The structure that makes spores. |
| Epiphyte | A plant that grows on another plant without harming it. |
Key Takeaways
- A fern is a vascular plant that reproduces by spores, with no flowers or seeds.
- The leafy fern you see is the diploid sporophyte stage.
- Spores grow into a small, haploid gametophyte called a prothallus.
- Sperm must swim in water to reach an egg, so ferns need damp conditions.
- Sori are clusters of spore-making sporangia, not a disease.
- Ferns range from tiny aquatic plants to tree ferns about 24 meters tall.
- Ferns date back about 420 million years and number roughly 10,500 to 12,000 species.
Frequently Asked Questions
Do ferns have seeds?
No. Ferns reproduce by spores. A spore grows into a tiny gametophyte, and that stage makes the eggs and sperm. The fertilized egg then grows into the leafy plant.
What are the brown dots under a fern leaf?
They are sori, clusters of sporangia that make spores. They are a normal part of a healthy fern, not a fungus or a disease.
Are ferns mosses?
No. Mosses are nonvascular, so they have no tubes for water and sugars. Ferns are vascular plants, which is one reason they can grow much larger.
Why do ferns grow in damp, shady places?
Their sperm must swim to the egg through a film of water, and the gametophyte dries out easily. Damp shade gives both stages the water they need.
Key references
• OpenStax Biology 2e: Seedless vascular plants
• USDA Forest Service: Fern structure
• American Fern Society: About ferns
• New York Botanical Garden: Ferns
• University of Maine Extension: Ostrich fern fiddleheads
• PMC: Response of nitrogen-fixing water fern Azolla to rice crop (2015)
Images: Wikimedia Commons, with the author and license named in each caption. This article is general science education.
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