Stem and Types of Stem

A stem is one of the two main structural axes of a vascular plant. The other is the root. The stem holds up the leaves, flowers and fruits. It also carries water and dissolved minerals up from the roots, and sugars down from the leaves to the parts of the plant that need them. Depending on the plant, a stem can also store food, photosynthesise, and make new plants.

A stem is built from nodes and internodes. The nodes are the points where leaves, buds or adventitious roots attach. The internodes are the stretches between them. This node-and-internode pattern is one of the easiest ways to tell a stem from a root, which does not carry leaves or buds at regular points along its length.

Most stems grow above ground, but some plants keep their stems underground, where they store food and help the plant survive from one season to the next. This article takes the stem from its basic structure through its three main types and the special forms some stems take.

The Parts of a Stem

A stem is more than a stalk. Look at it in cross-section and you find a set of tissues, each with a job.

Nodes and Internodes

The node is the joint. Leaves attach here, and buds sit in the axil of each leaf, ready to grow into a branch, a flower or a new shoot. Adventitious roots can also grow from nodes, which is why a stem cutting often roots at the nodes when put into soil or water.

The internode is the stem between two nodes. Its length sets how spread out the leaves are. A short internode gives a compact plant; a long one gives a stretched one. Some houseplants grow very long internodes when they reach for light.

The Vascular Tissues: Xylem and Phloem

Two pipe-like tissues run through every stem. Xylem carries water and dissolved minerals upward from the roots. Phloem carries the sugars made in the leaves to wherever the plant needs them — the roots, a storage organ, a growing shoot or a fruit.

The leaves that make the sugar are the source. The roots, storage organs, flowers and fruits that use or store it are the sink. The direction of phloem flow depends on where the sinks are, which is why phloem can move food up or down as the plant needs.

Between the xylem and the phloem in a dicot stem sits the vascular cambium, a thin sheet of dividing cells. It is the engine of secondary growth, the thickening that turns a young green stem into a woody one. Monocot stems generally do not have this cambium, which is one reason a palm tree thickens very differently from an oak.

A labeled diagram of a typical plant stem in cross-section, showing the epidermis, cortex, vascular bundles, pith and other tissues. Image: Curtis Clark, public domain, via Wikimedia Commons

The Three Main Types of Stem

Stems are often grouped into three broad types by their texture and how long they live: herbaceous, woody, and underground. These are not rigid boxes. A plant can have more than one kind of stem in its life, and some stems sit between categories. But the three-type frame is a good starting point.

Herbaceous Stems

An herbaceous stem is soft, green and flexible, with little or no woody tissue. The word herbaceous does not mean the plant is an herb in the culinary sense; it means the stem lacks the hard secondary xylem that makes a stem woody.

Herbaceous stems are found in non-woody plants such as grasses, ferns, and many flowering plants. A sunflower stalk, a tomato vine, a tulip flower stem and the culms of bamboo are all herbaceous.

Most herbaceous stems live for a single growing season and then die back. Perennial herbs survive from year to year not by keeping their above-ground stems, but by holding alive underground structures — rhizomes, bulbs, corms or roots. New herbaceous stems grow from these each spring. So a perennial herb still has herbaceous stems; it just does not keep them through the winter.

A transverse section of a Helianthus stem, showing the vascular bundles arranged in a ring inside the cortex, with the pith at the center. This ring arrangement is typical of dicot stems. Image: Jon Houseman, CC BY-SA 4.0, via Wikimedia Commons

Woody Stems

A woody stem is hard and rigid, built from secondary xylem — what we call wood. The wood gives the plant the strength to grow tall and live for many years. Woody stems are found in trees and shrubs.

A tree is a plant with a single main woody stem, the trunk, that usually branches high above the ground. A shrub is a woody plant with several stems branching near the soil. Both are built from wood, but they differ in form rather than in the basic stem type.

Woody stems grow in thickness through secondary growth. The vascular cambium, the sheet of dividing cells between the xylem and the phloem, adds new xylem to the inside and new phloem to the outside. The new xylem builds up year after year, and in climates with a winter pause this yearly rhythm shows up as a tree ring.

Not every woody stem comes from a dicot. Conifers — pines, firs, spruces — are gymnosperms, not dicots, but they have a vascular cambium and build wood in much the same way. Palms and bamboos, by contrast, are monocots, and they thicken without a typical vascular cambium, so a palm trunk does not show tree rings the way an oak trunk does.

Annual growth in a woody stem, plotted as the width of each year's ring against the age of the stem: the rings are widest while the plant is young and growth is fast, then narrow as it ages. Measuring that sequence is how dendrochronology dates wood. Image: Ninnel, CC BY-SA 4.0, via Wikimedia Commons

A cross-section of a tree trunk showing the concentric annual rings formed by secondary growth. Image: Arpingstone, public domain, via Wikimedia Commons

A labeled diagram of stem histology, showing the epidermis, cortex, vascular bundles with xylem and phloem, the vascular cambium, and the central pith. Image: SuperManu, public domain, via Wikimedia Commons

Underground Stems

Some stems live underground. An underground stem is a stem, not a root, and the difference matters: a stem carries nodes and buds, and often scale leaves, while a root does not.

Underground stems store food and help the plant survive from one season to the next. They can also start new plants. The main types are bulbs, corms, rhizomes, tubers and runners — and several of them are stems people commonly mistake for roots.

A micrograph showing the cork cambium (phellogen) in a young woody stem. The cork cambium is the lateral meristem that produces the periderm, the bark-like replacement for the epidermis in older stems. Image: Kje4532, CC BY-SA 4.0, via Wikimedia Commons

Special Forms of Stem

Many stems are modified for storage, for reproduction, or for both. The same three tissues — epidermis, ground tissue and vascular tissue — are still there, but the shape has changed to suit a special job. The forms below are all stems, even when they are called roots in everyday speech.

Bulbs

A bulb is a short, upright underground stem with fleshy storage leaves attached. The stem itself is the small disc at the base, called the basal plate, from which the roots grow downward and the shoot grows upward. The storage leaves are the thick fleshy layers that most people think of as the bulb.

Onions, garlic, daffodils and tulips grow from bulbs. A bulb often splits to form new bulbs, or produces small bulblets, which is why a clump of daffodils gets bigger each year.

A diagram of an onion bulb, the underground bud whose fleshy storage leaves wrap around a short stem. Image: சஞ்சீவி சிவகுமார், CC BY-SA 3.0, via Wikimedia Commons

Corms

A corm is a short, swollen, upright underground stem that stores food in its own tissue rather than in attached leaves. A corm is solid, not layered like a bulb. A thin covering of dry scale leaves protects it.

Crocus, gladiolus and taro grow from corms. Like bulbs, corms can produce new corms beside the old one, which is how the plant multiplies.

A Crocus corm: a short, upright underground stem covered in thin scale leaves and storing food in its own solid tissue. Image: Hüseyin Cahid Doğan, CC BY-SA 4.0, via Wikimedia Commons

Rhizomes

A rhizome is a horizontal underground stem. It grows sideways beneath the soil and throws up new shoots at its nodes, so a plant with rhizomes often spreads into a colony. Rhizomes also store food.

Ginger, bamboo, iris, ferns and turmeric are familiar rhizomes. Ginger and turmeric are harvested for the food stored in the rhizome. Bamboo spreads aggressively through its rhizomes, which is why a bamboo patch can expand so quickly.

A fresh ginger rhizome, a horizontal underground stem that stores food and produces new shoots from its buds. Image: Rasbak, CC BY-SA 3.0, via Wikimedia Commons

Tubers

A tuber is a swollen underground stem adapted for storage. The classic example is the potato. A potato tuber is a stem, not a root. The proof is the eyes: each eye is a bud at a node, and a node is a stem feature, not a root feature.

A tuber forms when the tip of an underground stem, often a stolon, swells with stored food. The buds (eyes) can each grow into a new plant, which is why a seed potato cut into pieces, each with at least one eye, will grow.

The sweet potato is different. It is a storage root, not a stem tuber. It develops from a root, not from a stem, and it does not have the nodes and buds that mark a potato tuber. The two are both harvested underground and both store food, but one is a stem and the other is a root.

A potato tuber that has started to sprout: the buds, or eyes, at the nodes push out shoots. Buds at nodes are what make a potato a stem tuber rather than a storage root. Image: MOs810, CC BY-SA 4.0, via Wikimedia Commons

Runners and Stolons

A runner, or stolon, is a horizontal stem that grows along or just above the ground and roots at its nodes to form new plants. It is a stem used for asexual reproduction, not a root.

Strawberries are the best-known example. A strawberry plant sends out runners that creep across the soil surface; where a runner touches the ground, it roots and starts a new plant. Spider plants do the same thing indoors, which is why a spider plant in a hanging pot often grows baby plants on long stems.

A strawberry plant sending out a runner (stolon), a horizontal above-ground stem that roots at its nodes to form new plants. Image: Françoise Foliot, CC BY-SA 4.0, via Wikimedia Commons

Runners, rhizomes and tubers all help a plant spread and survive. They are the plant’s way of making new people without flowers, pollen or seeds — vegetative reproduction, using a modified stem.

Why the Stem Matters

The stem is the bridge between the roots and the leaves. It holds the leaves up to the light, carries water up and food down, and stores surplus for lean times. Without a working stem, a plant cannot move what it makes to where it is needed.

The three main types — herbaceous, woody and underground — are really three answers to the same question: how should this plant hold itself up and live through the seasons? A soft green stem is cheap to build and good for a single season. A woody stem is expensive but long-lived. An underground stem hides from frost, drought and grazing, and wakes up when the season returns.

And once you know to look for nodes and buds, you can tell a stem from a root in the vegetable patch and in the wild. The potato in the cupboard is a stem. The carrot beside it is a root. That difference is not just botany; it is the difference between a plant part that can sprout into a new plant from its buds and one that cannot.

Key Terms in Plain English

These are the words in this article that would send you to a dictionary. Each one is given here the way it is actually used above.

Term	What it means
Stem	One of the two main structural axes of a vascular plant, the other being the root. It supports leaves, flowers and fruits and transports water and food.
Node	The point on a stem where a leaf, bud or adventitious root attaches.
Internode	The stretch of stem between two nodes.
Bud	An embryonic shoot, usually in the axil of a leaf, that can grow into a branch, a flower or a new shoot.
Xylem	The vascular tissue that carries water and dissolved minerals upward from the roots.
Phloem	The vascular tissue that carries sugars from the leaves to the parts of the plant that need them.
Vascular cambium	A thin sheet of dividing cells between the xylem and phloem in a dicot stem, which adds new xylem inside and new phloem outside, producing secondary growth.
Secondary growth	The increase in stem thickness produced by the vascular cambium and cork cambium, which makes wood in woody plants.
Wood	Secondary xylem, the hard tissue that builds up in the stems of trees and shrubs over many years.
Tree ring	A concentric layer of secondary xylem laid down in one year, visible in a cross-section of a woody stem in climates with a seasonal pause in growth.
Herbaceous	Describing a stem with little or no woody tissue; soft, green and flexible, and usually living for a single growing season.
Woody	Describing a stem with hard secondary xylem, as in trees and shrubs.
Tree	A woody plant with a single main stem, the trunk, that usually branches high above the ground.
Shrub	A woody plant with several stems branching near the soil.
Monocot	One of the two great groups of flowering plants, with scattered vascular bundles in the stem and usually no vascular cambium; grasses and palms are monocots.
Dicot	One of the two great groups of flowering plants, with vascular bundles in a ring in the stem and usually a vascular cambium that produces secondary growth.
Gymnosperm	A seed plant whose seeds are exposed, usually on the scales of a cone; pines, firs and cycads are gymnosperms.
Bulb	A short underground stem with a basal plate and fleshy storage leaves attached, as in onion, garlic and daffodil.
Basal plate	The small disc of stem tissue at the base of a bulb, from which roots grow downward and the shoot grows upward.
Corm	A short, solid, swollen underground stem that stores food in its own tissue, as in crocus and gladiolus.
Rhizome	A horizontal underground stem that grows sideways and throws up new shoots at its nodes, as in ginger, bamboo and iris.
Tuber	A swollen underground stem adapted for storage, with buds (eyes) at its nodes; the potato is a stem tuber.
Storage root	A swollen root that stores food, as in the sweet potato and carrot; a storage root has no nodes or buds, unlike a stem tuber.
Stolon (runner)	A horizontal stem that grows along or just above the ground and roots at its nodes to form new plants, as in strawberry and spider plant.
Vegetative reproduction	Asexual reproduction from a part of the plant such as a stem, rhizome, bulb or tuber, without flowers, pollen or seeds.

Key terms used in this article, defined for quick reference.

Key Takeaways

• A stem is one of the two main axes of a vascular plant, the other being the root; it supports leaves, flowers and fruits and carries water up and food down.
• Stems are built from nodes, where leaves and buds attach, and internodes, the stretches between them.
• The two vascular tissues are xylem, which carries water upward, and phloem, which carries sugars from source to sink.
• The vascular cambium between xylem and phloem produces secondary growth, the thickening that makes wood in woody stems.
• The three main stem types are herbaceous (soft, green, flexible), woody (hard, with secondary xylem), and underground (modified for storage and survival).
• Perennial herbs survive the winter through underground structures such as rhizomes, bulbs and corms; their above-ground stems are still herbaceous.
• A bulb is a short underground stem with fleshy storage leaves and a basal plate; a corm is a solid swollen stem, not layered like a bulb.
• A rhizome is a horizontal underground stem that spreads the plant. A tuber is a swollen underground stem with buds at its nodes. A runner is a horizontal above-ground stem that roots at its nodes.
• A potato is a stem tuber (it has eyes at nodes); a sweet potato is a storage root (it has no nodes or buds).
• Conifers are gymnosperms with a vascular cambium and secondary xylem, so they make wood like dicots; palms and bamboos are monocots and thicken without a typical vascular cambium.

Frequently Asked Questions

What is the main function of a stem?

A stem supports the leaves, flowers and fruits. It transports water and dissolved minerals up from the roots in the xylem, and sugars from the leaves to the rest of the plant in the phloem. Some stems also store food, photosynthesise, and make new plants.

What is the difference between a node and an internode?

A node is the point on a stem where a leaf, bud or adventitious root attaches. An internode is the stretch of stem between two nodes. Nodes are a stem feature; roots do not have them.

What is the difference between xylem and phloem?

Xylem carries water and dissolved minerals upward from the roots. Phloem carries the sugars made in the leaves to wherever the plant needs them — roots, storage organs, flowers and fruits. Xylem flow is always upward; phloem flow moves from source to sink and can go up or down.

What makes a stem woody?

A woody stem has secondary xylem, or wood, laid down year after year by the vascular cambium. The cambium adds new xylem to the inside and new phloem to the outside, and the buildup of xylem is what makes the stem hard and thick. In climates with a winter pause this yearly growth shows as a tree ring.

Is a potato a root or a stem?

A potato is a stem tuber. The eyes are buds at nodes, and nodes and buds are stem features, not root features. A sweet potato, by contrast, is a storage root — it develops from a root and has no nodes or buds.

What is the difference between a bulb and a corm?

A bulb is a short underground stem with fleshy storage leaves attached and a small basal plate at the base; an onion is a bulb. A corm is a solid, swollen underground stem that stores food in its own tissue, not in attached leaves; a crocus is a corm. A bulb is layered; a corm is solid.

Is bamboo a tree?

Bamboo is not a tree. It is a monocot, related to grasses, and its stems are herbaceous in the botanical sense even though some species grow very tall and woody-looking. A bamboo stem thickens without a typical vascular cambium and does not produce tree rings.

What is a runner or stolon?

A runner, or stolon, is a horizontal stem that grows along or just above the ground and roots at its nodes to form new plants. Strawberries and spider plants use runners for vegetative reproduction.

Key references
• Plant stem — functions, structure and specialized forms
• Stems — structure, functions and types (Huntington Library)
• Stems: The Plants’ Highway System (CK-12)
• Types of stems (Botanical-online, Vicente Martínez Centelles)
• Stems — classification and structure (Britannica)
• Dicot and monocot stems compared (Visible Body)
• Stolon / runner (Magnoliophyta glossary)
• Runners — layering (University of Florida IFAS)
• Tubers and root vegetables — the difference (Extension)
• Tuber types (Botanical-online)
• Potato tuber structure (Wikimedia Commons file page)

Sources: the Wikipedia article on plant stems, for the definition of a stem as one of the two main axes, its node-and-internode structure, the functions of stems (support, transport of water and solutes, storage, photosynthesis, production of new tissue), and the specialized forms (bulb, corm, rhizome, tuber, stolon/runner) and their botanical definitions; the Huntington Library page on stems, for the two main functions of support and transport; the CK-12 stem lesson, for the source-to-sink description of phloem transport; the Botanical-online article on types of stems by Vicente Martínez Centelles, for the herbaceous-versus-ligneous classification and the tree / shrub / bush heights; the Britannica article on stems, for corms as short upright underground stems surrounded by thin scale leaves and for bulbs having a greatly reduced stem; the Visible Body page on monocot and dicot stems, for the ring-versus-scattered arrangement of vascular bundles and the presence or absence of a vascular cambium; the Magnoliophyta glossary definition of stolon, for the runner as a horizontal stem rooting at the nodes; the University of Florida IFAS page on runners, for the strawberry runner as a specialized stem growing horizontally from the crown and forming a new plant at the nodes; the Extension FAQ on tubers and root vegetables, for the distinction between a stem tuber (potato) and a root tuber (sweet potato); and the Botanical-online page on tuber types, for the potato eye as a node with buds. Each source was opened and read in full. The node-and-internode structure, the xylem/phloem transport directions, the vascular cambium and secondary growth, the dicot ring versus monocot scattered bundles, the bulb basal plate, the corm as a solid stem, the rhizome as a horizontal stem, the tuber as a stem with buds at nodes, the sweet potato as a storage root, and the runner as an above-ground stem rooting at the nodes all follow these sources. The correction of the V1’s dicot/conifer split inside woody stems — conifers are gymnosperms with a vascular cambium and secondary xylem, so the better contrast is secondary growth present versus absent — follows the Visible Body and Wikipedia comparisons of monocot and dicot stems. Figures are from Wikimedia Commons under the license named in each caption. This article is written for education.