Roots and Their Types in Flowering Plants: A Complete Guide

A flowering plant is usually judged by what grows above the ground. The roots below it do most of the quiet work, and they are just as varied as the shoots they feed.

This guide covers what roots do and the two main root systems. It also looks at the parts of a young root, the shapes roots take in special cases, and the microbes that share the soil with them.

What Roots Do for a Plant

Four Jobs Every Root System Shares

A root system anchors the plant in the soil. It also absorbs water and dissolved minerals, and it passes both upward to the shoot through the xylem. Many roots go further and store food for later use.

Some roots take on extra work. Prop roots and buttress roots steady a large tree, and climbing roots let a vine grip a wall or a trunk.

Where Water and Minerals Really Enter

It is tempting to picture the whole root soaking up water like a sponge. Most absorption happens instead in the young regions that carry root hairs, which sit in the zone of maturation near the tip.

Water crosses into the root by osmosis, moving down its concentration gradient across selectively permeable membranes. Mineral ions are a mixed case: some slip in passively, while others must be pulled in against their gradient, and that step costs energy.

Taproots and Fibrous Roots

The Taproot System

A taproot system is built around one dominant primary root that grows straight down. Smaller lateral roots branch from it, and they are often called secondary roots.

This is the common pattern in eudicots, the group older textbooks call dicots. Familiar taproots include carrot, beet and dandelion, and the seedlings of many oaks start with one too.

The Fibrous Root System

A fibrous root system has many roots of similar size and no dominant main root. Most of them arise from the base of the stem rather than from a single primary root.

Grasses show this best, and wheat, rice and corn are the standard examples. Fibrous roots spread widely near the surface, which suits plants that need to catch rain quickly.

A Trend, Not a Rule

It is useful to link fibrous roots with monocots and taproots with eudicots. Treat that link as a general pattern rather than a test, because root shape can change as a plant ages or as the soil changes around it.

Two root systems side by side. A taproot has one dominant root with lateral branches; a fibrous system has many roots of similar size. Image: KaitlinLiu, CC BY-SA 4.0, via Wikimedia Commons

Inside a Young Root

Four Zones from the Tip Upward

At the very tip sits the root cap, a loose protective cap that eases the root through the soil. Just behind it is the zone of cell division, which holds the apical meristem.

Above that is the zone of elongation, where new cells stretch and push the tip deeper. The zone of maturation follows, and this is where root hairs appear and where most absorption takes place.

Root Hairs Are Not Tiny Roots

A root hair is a thin extension of a single epidermal cell. It is not a small branch, and it does not last long, but a dense fringe of them adds a great deal of absorbing surface.

A Cross Section: Epidermis to Stele

In a cross section, the outer layer is the epidermis and the broad tissue inside it is the cortex. The endodermis seals the inner edge of the cortex, and its waxy Casparian strip forces water and minerals to pass through cells rather than between them.

Just inside the endodermis lies the pericycle, which can start a lateral root. The central stele holds the xylem and phloem, the pipeline that carries water up and food down.

A root tip under the microscope. The root cap protects the growing point, and the zones behind it lengthen and mature as the root grows. Image: SuperManu, CC BY-SA 2.5, via Wikimedia Commons

Roots That Have Changed Shape

Storage Roots

A storage root is a root that has swollen with food. Carrot, turnip and beet store theirs in a taproot, and all three are roots rather than underground stems.

The sweet potato is also a storage root. A potato is not, since it is a modified stem with buds that can sprout, which a true root cannot do.

A wild carrot lifted from the soil. The single fleshy root is a taproot, the same form that farmed carrots have been bred to exaggerate. Image: Forest and Kim Starr, CC BY 3.0 US, via Wikimedia Commons

Prop Roots and Brace Roots

Prop roots grow out of the stem or a branch and reach the ground, then act like extra pillars. The banyan tree shows the effect at its most dramatic, because its prop roots thicken into trunk-like columns.

Maize grows brace roots from the lower stem just above the soil. They are adventitious roots that steady a tall, top-heavy plant, and they are often called prop roots as well.

Inside the crown of a great banyan. Roots that drop from the branches take hold in the soil and thicken into supporting columns. Image: Abhijit Kar Gupta, CC BY 2.0, via Wikimedia Commons

Stilt Roots and Breathing Roots

Some mangroves hold themselves up with stilt roots, which arch from the stem down into the mud. Other mangroves send up pneumatophores, roots that grow upward out of waterlogged soil to take in air.

It is worth keeping those two apart. A stilt root is about support, while a pneumatophore is the breathing root, so not every aboveground mangrove root is a breathing root.

Climbing and Aerial Roots

Climbing roots let a plant scale a surface. The juvenile English ivy grows adventitious roots along its stems that cling to bark and stone.

Aerial roots belong to epiphytes such as many orchids, which live on other plants without robbing them. Their exposed roots can take in moisture from the damp air around them.

Roots and Their Partners

Mycorrhizae: Roots Plus Fungi

A mycorrhiza forms when a fungus and a root grow together. In an ectomycorrhiza the fungal threads wrap the root and weave between its outer cells, while in an arbuscular mycorrhiza they enter the root cells and branch inside them.

Either way the partnership is a trade. The fungus reaches water and minerals, especially phosphorus, that the root would miss on its own, and the plant supplies the fungus with sugars made in its leaves.

Nitrogen-Fixing Nodules

Legumes such as beans, peas and peanuts take the idea further. Soil bacteria called rhizobia enter their roots, which respond by building small nodules.

Inside a nodule the bacteria convert nitrogen gas from the air into a form the plant can use. That ability is not a general property of roots, and a few plants outside the legumes form such nodules as well.

Pink nodules on clover roots. The pink color comes from the same oxygen-binding pigment that lets the bacteria fix nitrogen without being poisoned by oxygen. Image: Bwiltz, CC BY-SA 4.0, via Wikimedia Commons

Key Terms in Plain English

Term	What it means here
Taproot	One dominant primary root with smaller lateral roots branching off it.
Fibrous root	A system of many roots of similar size with no dominant main root.
Primary root	The first root of the plant, which grows out of the embryo's radicle.
Lateral root	A branch root that starts from an existing root.
Adventitious root	A root that starts from stem or leaf tissue instead of another root.
Root cap	The loose protective tissue covering the growing tip of a root.
Apical meristem	The zone of dividing cells that lengthens the root.
Root hair	A thin extension of one epidermal cell that absorbs water and minerals.
Epidermis	The outer cell layer of the root.
Cortex	The tissue between the epidermis and the endodermis.
Endodermis	The inner boundary of the cortex, which controls what enters the stele.
Casparian strip	A waxy band in the endodermis that blocks flow between cells.
Pericycle	The layer inside the endodermis that can begin a lateral root.
Stele	The central cylinder of the root, containing xylem and phloem.
Prop root	A root from a stem or branch that reaches the ground and supports the plant.
Pneumatophore	An upward-growing root that takes in air in waterlogged soil.
Mycorrhiza	A partnership between a root and a fungus.
Nodule	A small root swelling where nitrogen-fixing bacteria live.

Key Takeaways

• Roots anchor the plant, absorb water and minerals, carry them to the shoot, and often store food.
• A taproot system has one dominant root; a fibrous system has many roots of similar size.
• The monocot and eudicot pattern is a tendency, not a rule that names every plant.
• A young root has a cap, a dividing zone, an elongating zone and a maturing zone with root hairs.
• Modified roots support, store food, breathe or climb, and each shape has a name.
• Mycorrhizae and rhizobial nodules let roots trade with fungi and bacteria.

Frequently Asked Questions

What is the difference between a taproot and a fibrous root?

A taproot system has one main root that outgrows the rest, with lateral roots branching from it. A fibrous system has many roots of about the same size and no single dominant root.

Do all monocots have fibrous roots?

Fibrous and adventitious roots are typical of monocots, and taproots are typical of eudicots. It is a strong general trend, but root form can shift with age and soil, so it does not identify every plant on its own.

Is a root hair the same as a lateral root?

No. A root hair is a thin extension of a single surface cell and lives briefly. A lateral root is a new root that starts inside the parent root and grows out through the cortex.

Is a sweet potato a root or a stem?

A sweet potato is a storage root. A potato is a modified stem, which is why it has buds that can sprout, while a true root carries no buds.

Key references
• OpenStax Biology 2e: Roots
• OpenStax Biology 2e: The Plant Body
• NC State Extension: Extension Gardener Handbook, Botany
• University of Minnesota: Horticulture, Roots
• UC Davis botany text: Root Modifications
• Steffens and Rasmussen: The Physiology of Adventitious Roots
• New Mexico State University Extension: Nitrogen Fixation by Legumes
• University of Wisconsin Extension: Mycorrhizae

Images: Wikimedia Commons, with the author and license named in each caption. Root form can change with age and growing conditions, so the categories here describe the usual pattern rather than a fixed rule.