Ferns, horsetails and club mosses belong to a group of plants called pteridophytes. They carry water through their stems and leaves, and some of their extinct relatives grew as tall as trees. Yet they never make flowers, and they never make seeds.
That combination is what makes the group worth a close look. Pteridophytes sit between the mosses, which have no water-carrying plumbing, and the seed plants, which wrap their young inside a seed. This guide explains what holds the group together, how its members live, and where they fit in the plant kingdom today.
What Counts as a Pteridophyte
A Grade, Not a Single Branch
A clade is a group that contains one ancestor and all of its descendants. A grade is a looser label. It collects living things that share a level of organization, and it leaves some of the descendants out.
Pteridophytes are a grade. The name gathers every vascular plant that reproduces with spores, so it leaves out the seed plants even though seed plants share the same vascular ancestor. Botanists still use the word because it is handy, but it does not name one branch of the family tree.
The Four Living Groups
Four groups of spore-bearing vascular plants survive today. Ferns, horsetails and whisk ferns form one large lineage, the monilophytes. Club mosses, spike mosses and quillworts form the other lineage, the lycophytes.
| Group | Everyday name | Leaf type | Living species |
| Polypodiopsida | Ferns | Megaphylls, with branched veins | About 10,500 to 12,000 |
| Equisetopsida | Horsetails | Greatly reduced megaphylls | About 15 to 20 |
| Ophioglossopsida | Whisk ferns | Reduced or absent | About a dozen |
| Lycopodiopsida | Club mosses, spike mosses, quillworts | Microphylls, with one vein | About 1,200 to 1,350 |
Horsetails and whisk ferns are a small slice of the total. Add the groups together and the grade holds roughly 12,000 to 13,000 living species.
The exact totals differ from one source to the next. New species are still being described, and botanists do not all draw the group boundaries in the same place, so treat every count here as an estimate.
Vascular Tissue: The Feature That Set Them Apart
Xylem, Phloem and Tracheids
Vascular tissue is a set of tubes. Xylem carries water and dissolved minerals up from the roots. Phloem carries sugars and other substances around the plant. Together they form a internal transport network.
The water-carrying cells in most pteridophytes are tracheids. A tracheid is a long cell with a stiff wall and small pits that let water slip sideways into the next cell. The stiffness comes from lignin, a material that also helps hold the plant upright.
Transport plus support is what allowed these plants to grow tall. A moss can only move water by soaking it up and passing it from cell to cell, which keeps mosses low and close to wet ground.
Microphylls and Megaphylls
Lycophyte leaves are microphylls. They are usually small and carry a single unbranched vein. Ferns and horsetails have megaphylls, leaves with branched or multiple veins. A fern frond is a clear megaphyll.
True roots, stems and leaves are organs of the plant body, not just surfaces that look similar. Whisk ferns are the exception that proves the rule: their roots and leaves have been reduced so far that the stems do most of the work.
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| A stained cross-section through a bracken fern stem. The dark clusters are the vascular bundles that carry water and sugars. Image: Anatoly Mikhaltsov, CC BY-SA 4.0, via Wikimedia Commons |
A Life Cycle With Two Very Different Plants
The Sporophyte Is the Plant You See
The fern or horsetail you notice is the sporophyte. It is diploid, which means each of its cells holds two sets of chromosomes. It grows by ordinary cell division and can live for many years.
When it is ready to reproduce, the sporophyte makes spores by another kind of division. Each spore has a single set of chromosomes, so it is haploid.
The Gametophyte Is Small and Mostly Independent
A spore that lands in a damp spot grows into a gametophyte. That stage is haploid too. In most pteridophytes it is small, green and free-living, and it makes the eggs and sperm on its own.
Not every gametophyte works that way. The gametophytes of whisk ferns and of some club mosses grow underground and take their food from fungi instead of from sunlight.
Why Fertilization Still Needs Water
The sperm have tails and must swim to reach an egg. They can only travel through a thin film of water. Without rain, dew or wet soil, fertilization fails, no matter how healthy the plant looks.
That single requirement explains a lot. It is the main reason so many pteridophytes live in damp, shaded places, and it is the weakness that seed plants later overcame.
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| Rough horsetail (Equisetum hyemale). Horsetails carry water through jointed, silica-rich stems. Image: Diego Delso, CC BY-SA 4.0, via Wikimedia Commons |
How Pteridophytes Make Spores
Sporangia, Sori and the Indusium
A sporangium is the case in which spores form. Many ferns pack their sporangia into clusters called sori, usually on the underside of a frond. Some ferns shield each sorus with a small flap of tissue called an indusium; others have none.
Sporangia develop in two ways. Eusporangiate sporangia start from several initial cells and end up with thick walls. Leptosporangiate sporangia start from a single cell and have thin walls. Most fern species are leptosporangiate.
Strobili: Cones on Club Mosses and Horsetails
Club mosses, spike mosses and horsetails gather their sporangia on cone-like structures called strobili. Each strobilus is a tight cluster of small leaves that carry the sporangia.
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| A microscope view of a Selaginella strobilus. The rounded sacs are microsporangia, which hold the smaller of the two spore types. Image: ShoroborShukanta, CC BY 4.0, via Wikimedia Commons |
One Kind of Spore or Two?
Most ferns are homosporous: they make a single kind of spore, and the gametophyte it grows into can produce both eggs and sperm.
Some pteridophytes are heterosporous. They make small microspores and larger megaspores. Selaginella is a heterosporous club moss. Its gametophytes develop inside the spore wall, one sex per spore.
From Coal Forests to Today
Scale Trees and Calamites
During the Carboniferous Period, about 359 to 299 million years ago, giant relatives of today's club mosses grew in swampy forests. Lepidodendron is the best known. This scale tree could reach about 30 meters, and its trunk was covered in a pattern of leaf scars that looks like reptile skin.
Calamites were horsetail relatives from the same forests. Some grew tree-sized. Published height estimates disagree, so treat any exact figure as rough.
What Actually Made the Coal
Coal forms when plant material piles up in waterlogged, oxygen-poor ground, escapes complete decay, and is later buried and compressed. Scale trees were major contributors to Carboniferous coal, but they were not the only ones.
Coal-swamp communities also held ferns, horsetail relatives and early seed plants. The plants nicknamed seed ferns belonged to that last group, so despite the name they were seed plants rather than true ferns.
Why Seed Plants Won Most Habitats
Seeds and pollen changed the rules. Pollen carries sperm cells through the air, so fertilization no longer needs a film of water. A seed protects the young plant, feeds it, and can wait for better conditions before it grows.
It is too simple to say seed plants wiped pteridophytes out. Seed plants spread into drier habitats, and flowering plants later added flowers and fruits. Pteridophytes simply kept the wet, shaded ground.
Where Pteridophytes Thrive Now
Ferns fill moist understory layers, and some grow on tree trunks and rocks. Horsetails favor wet ground, stream edges and disturbed sites. Bracken can regrow within weeks of a fire, because its underground stems survive the heat.
A global assessment estimated that about 16 percent of pteridophytes are threatened with extinction. That number comes from a sample of species, so read it as an estimate rather than a complete census.
One last oddity: horsetail stems take up silica from the soil, which makes them abrasive. That is why Equisetum was once used to scour pots and polish metal.
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| A reconstruction of Lepidodendron, a scale tree of the Carboniferous coal forests. Image: Falconaumanni, CC BY-SA 3.0, via Wikimedia Commons |
Key Terms in Plain English
| Term | What it means here |
| Pteridophyte | A vascular plant that reproduces with spores instead of seeds. |
| Vascular tissue | Tubes that move water, minerals and sugars through a plant. |
| Xylem | The vascular tissue that carries water and minerals upward. |
| Phloem | The vascular tissue that carries sugars around the plant. |
| Tracheid | A long, lignified water-carrying cell in the xylem. |
| Lignin | A stiff material in cell walls that helps support the plant. |
| Microphyll | A small leaf with a single unbranched vein. |
| Megaphyll | A leaf with branched or multiple veins. |
| Sporophyte | The diploid stage that makes spores, and the plant you see. |
| Gametophyte | The haploid stage that makes eggs and sperm. |
| Sporangium | The case in which spores are made. |
| Sorus | A cluster of sporangia, often on the underside of a frond. |
| Indusium | A flap of tissue that covers a sorus in some ferns. |
| Strobilus | A cone-like cluster of leaves that carry sporangia. |
| Homosporous | Making one kind of spore. |
| Heterosporous | Making two kinds of spore, microspores and megaspores. |
Key Takeaways
- Pteridophytes are vascular plants that reproduce with spores, not seeds.
- The name is a grade, not a single branch: it covers lycophytes and monilophytes.
- Xylem and phloem let these plants move water and grow tall, unlike mosses.
- The sporophyte is diploid and dominant; the gametophyte is haploid and usually small.
- Sperm must swim through water, so fertilization still needs damp conditions.
- Carboniferous scale trees were major, but not the only, source of coal.
Frequently Asked Questions
Are pteridophytes the same as ferns?
No. Ferns are the largest group inside the grade, but club mosses, spike mosses, quillworts, horsetails and whisk ferns are pteridophytes too.
Do club mosses count as mosses?
No. Club mosses are vascular lycophytes with true leaves called microphylls. True mosses are bryophytes, with no true xylem or phloem.
Why do pteridophytes need water to reproduce?
Their sperm have tails and must swim to an egg. A film of water is the only road between them, which is why damp habitats suit these plants so well.
Are pteridophytes primitive plants?
They are not unfinished versions of seed plants. They are living, diverse lineages with their own working solutions, and many of them are thriving today.
Key references
• OpenStax Biology 2e: Seedless vascular plants
• OpenStax Biology 2e: Early plant life
• PPG I: A community-derived classification for extant lycophytes and ferns (2016)
• American Fern Society: About ferns
• UC Museum of Paleontology: Carboniferous Period
• Natural History Museum: Pteridophyte conservation assessment
Images: Wikimedia Commons, with the author and license named in each caption. This article is general science education.
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