3-Panel figure, photos of fossils preserving branches. Panel 1: Apical branching in Lepidodendron. Panel 2: Non-axillary lateral branching in Asterophyllites. Panel 3: Axillary lateral branching in dawn redwood (Metasequoia)

Branching


Feature image: Fossil plants showing different types of branching. Left: Stem of a scale tree (Lepidodendron, a lycophyte, Carboniferous, Ohio, U.S.A.) showing a dichotomy, the result of apical branching. Center: Asterophyllites (an extinct relative of horsetails, Pennsylvanian, Pennsylvania, U.S.A.) branches with whorls of leaves; branching is lateral but not axillary. Right: Branchlets of an extinct dawn redwood (Metasequoia occidentalis, a conifer, Eocene, Washington, U.S.A.); branching is lateral and axillary, as in many seed plants. Credits: Lepidodendron YPM PB 054238 (by Fiona O'Brien); Asterophyllites YPM PB 000699 (by Robert Swerling); Metasequoia occidentalis YPM PB 005960 (by Linda S. Klise). All images from Yale Peabody Museum of Natural History (via GBIF, CC0 1.0/Public Domain Dedication).

Introduction

The sporophytes of most vascular plants branch within the normal course of their growth and development. Branching occurs when one axis (root or stem) divides, or when a smaller axis develops on a larger, more dominant axis. Branching of axes can occur apically (at the apex or tip of an axis) or laterally (on the side of an axis). Apical branching is the more ancient type of branching in both stems and roots; it is also structurally similar in stems and roots. True lateral branching developed in the euphyllophytes (the group including horsetails, ferns, and seed plants, as well as their extinct ancestors and relatives) and takes places via different processes in shoot and root. In shoots, lateral branches develop from buds on the surface of the stem; lateral roots originate within the root from which they branch.

The first sections of this page will cover branching in shoots. Topics include apical branching, lateral branching, and adventitious branching. Next, monopodial and sympodial growth in laterally branching plants will be explained. Finally, root branching is briefly discussed at the end of this page.

Apical branching (dichotomous branching)

Apical branching is a type of branching in which the shoot apex divides, usually bifurcating to produce two branches. In the simplest type of apical branching, the apex divides to produce two equal branches. This type of apical branching is often simply called dichotomous, but is sometimes called isotomous (Greek isos = equal). Dichotomous branching was the earliest type of branching and is seen in some ancient plant sporophytes, like the Silurian to Devonian plant Cooksonia (typically considered an early vascular plant) and the Devonian plant Aglaophyton (a protracheophyte, a branching plant lacking true vascular tissue, shown below). Dichotomous branching is also seen in some modern plants like the firmosses (Huperzia, an example is shown below) and whisk ferns (Psilotum).

Sometimes, apical branching produces branches of unequal size. This type of branching is known as anisotomous (Greek anisos = unequal). If apical branching is extremely unequal, it may be called pseudomonopodial (Greek pseudēs = fake/false). A plant with pseudomonopodial branching or pseudomonopodial growth mimics the form of a plant with monopodial growth (discussed below). In other words, pseudomonopodial branching results in a plant that looks like it has a dominant ("main") stem and lateral (side) branches, even though branching is really apical. Unequal apical branching occurs in lycophytes and some extinct groups, like trimerophytes (the stem group to euphyllophytes, the group that includes ferns, horsetails, and seed plants).

Terminology note: "Dichotomous branching" is often used as a synonym for apical branching, encompassing both isotomous (equal) and anisotomous (unequal) types. In this case, a modifier (like "isotomous" or "equal") may be used to indicate the relative size of the branches.


Two diagrams showing apical branching. Diagram 1: A single stem bifurcates to form to equal stems. Diagram 2. A single stem bifurcates, but one branch becomes larger and dominates the other.
Apical branching. The diagrams above show variations in apical branching. In dichotomous branching, a stem apex bifurcates to form two equal branches. In pseudomonopodial branching, a stem apex divides and forms unequal branches, with one becoming dominant over the other. Credit: E.J. Hermsen (DEAL), after fig. 9.5 in Simpson (2010).

2-Panel photo figure. Panel 1: Shining firmoss showing a single dichotomy with two equal branches. Panel 2: Clubmoss that appears to have a central stem with lateral branching units.
Apical branching in extant lycophytes. These lycophyte growth forms result from different types of apical branching. Left: Shining firmoss (Huperzia lucidula) showing dichotomous branching; the branches are equal in size. Right: Clubmoss (Dendrolycopodium) showing pseudomonopodial branching, in which the plant appears to have a main stem and lateral branches; note also the dichotomizing branching pattern of the lateral branching units. (The structure at the tip of the central stem is a spore-producing cone.) Credit: E.J. Hermsen (DEAL).

2-Panel figure. Panel 1: Drawing showing a reconstructions of Aglaophyton major, a dichotomizing plant. Panel 2: Drawing showing a reconstruction of Psilophyton dawsonii, a plant with a mix of dichotomous and pseudomonopodial branching.
Apical branching in fossil plants. Reconstructions of Early Devonian plants that had apical branching. Left: Aglaophyton major, a protracheophyte from the Rhynie Chert of Scotland, had dichotomously branching axes; some of the axes ended in apical sporangia (spore-producing structures), and horizontal axes had rhizoids (thread-like anchoring structures). Right: Portion of Psilophyton dawsonii, a trimerophyte from Canada. This plant had large dichotomizing axes. Pseudomonopodial branching produced smaller, lateral axes; the lateral axes dichotomized to produce branching systems, some of which ended in sporangia. Note: Scale bar applies only to Aglaophyton. Credits: Aglaophyton major (Falconaumanni, via Wikimedia Commons, CC BY-SA 3.0); Psilophyton dawsonii (reconstruction by Elfriede Abbe, text-fig. 13 from Banks et al. 1975, via the Internet Archive, CC BY-NC-SA 3.0). Images modified from originals.

Lateral branching

In plants with lateral branching, a main stem grows from an apical bud or terminal bud (a region of the shoot tip that includes the apical meristem), and lateral (side) branches are produced from lateral buds, each with its own apical meristem. Thus, branching is not caused by division of the shoot apex.

Types of lateral branching
Axillary branching

In axillary branching, lateral branches grow from axillary buds, or buds the develop in the leaf axils. An axil is the angle formed between the the upper (adaxial) side of the leaf and the stem to which it is attached; the word axil comes from the Latin word axilla, meaning "armpit" (just remember: the axil is the armpit of the leaf!). Axillary buds—also called lateral buds—are just immature branches. An axillary bud may elongate to form a vegetative (sterile) branch, but it may also develop to form a fertile branch. A fertile branch is a reproductive structure like a cone or a flower. Axillary branching is found in many seed plants, including ginkgoes (Ginkgo), conifers, and angiosperms (flowering plants); axillary branching is absent in cycads.

Terminology note: Often, the term "axillary bud" is used when leaves are present, as "axillary" describes the position of the bud in the upper angle between leaf and stem. The term "lateral" may be preferred when leaves are shed (lost), because the position of the bud is no longer obviously axillary (without a leaf, there is no axil).


2-part figure showing diagrams illustrating axillary branching. Part 1: Portion of stem with a leaf and an axillary bud. Part 2. Portion of the same stem in which the axillary bud has elongated for form a branch.
Axillary branching. The diagrams above show axillary branching. The diagram on the left shows a portion of a stem with a single leaf. In the axil of the leaf is a bud. In the diagram on the right, the bud has elongated into a lateral branch. At this point, the leaf subtending (below) the bud may have been shed from the plant, so the axillary position of the branch may no longer be obvious. Notice also that the branch formed by the bud bears leaves, each of which has its own axillary bud that could elongate into a branch. The terminal bud, or shoot apex, is the growing point that contributes to elongation of the main branch. Credit: E.J. Hermsen (DEAL).

2-Panel photo figure. Panel 1: Branch of shellbark hickory with buds in the axils of the leaves. Panel 2. Branch of willow karee with a single axillary bud beginning to grow into a branch.
Axillary buds. Left: Portion of a shellbark hickory (Carya lacinosa, an angiosperm) branch showing axillary buds; these buds occur where the base of each leaf petiole (leaf stalk) attaches to the stem. Right: Portion of willow karee (Rhus angustifolia, an angiosperm) stem showing an axillary bud that is beginning to grow into a branch. Credits: Carya lacinosa (Plant Image Library, via Wikimedia Commons, CC BY-SA 2.0); Searsia angustifolia (Rhus angustifolia) (JonRichfield, via Wikimedia Commons, CC BY-SA 3.0). Images modified from originals.

Axillary bud primordia (bumps of tissue that will become buds) first appear near the apical meristem, developing soon after their associated leaves. Often, one axillary bud occurs per leaf axil. It should be noted, however, that some leaves may lack an axillary bud. Furthermore, in some plants more than one bud may occur in a single leaf axil; extra buds in addition to the typical axillary bud are called accessory buds.

Photo of a longitudinal section of a Coleus shoot apex with leaves, a bud, and a stem labelled.
Axillary bud development. Longitudinal section of the shoot apex of coleus (Coleus, an angiosperm) showing the development of leaves and their associated axillary buds. The first pair of leaf primordia (developing leaves) look like two horns on either side of the rounded shoot apex. These leaf primordia lack axillary buds. The next visible pair of leaves have bud primordia (developing axillary buds) in their axils; at this stage, the developing buds look like small bumps or swellings. Credit: Coleus shoot tip (BlueRidgeKitties, via flickr, CC BY-NC-SA 2.0). Image modified from original.

In some plants, axillary buds elongate right away to form branches. In other plants, axillary buds do not elongate to form branches immediately, but may remain inactive for a period of time. In woody plants, a bud will often elongate to form a branch after its associated leaf has been shed. In this case, a leaf scar will remain on the bark below the bud, marking the former position of the leaf.

2-Panel photo figure. Panel 1: Heart-shaped leaf scar in face view with bud above it. Panel 2. Leaf scar in later view with swollen bud above it.
Lateral buds. Two views of branches of tree-of-heaven (Ailanthus altissima, an angiosperm), showing lateral buds. Note that each bud sits above a heart-shaped leaf scar, the scar left on the bark when a leaf is shed. The marks inside the leaf scar are the positions of the vascular bundles that fed the leaf. The dots on the bark are lenticels (areas for gas exchange). Credits: Ailanthus altissima (AnRo0002, via Wikimedia Commons, CC0 1.0/Public Domain Dedication); Ailanthus altissima (Stefan.Iefnaer, via Wikimedia Commons, CC BY-SA 4.0). Images modified from originals.

Non-axillary lateral branching in pteridophytes

While branching in seed plants is typically axillary, lateral branches can also arise from non-axillary positions on a stem. In ferns, lateral branches can arise from a variety of positions on the stem. In horsetails (Equisetum), lateral branches originate from positions between the leaves. Because the tiny leaves in horsetails are fused into a sheath around the stem, the branches break through the leaf sheath during growth.


2-Panel photo figure. Panel 1: Marsh horsetail showing two whorls of developing branches, a leaf sheath, and a portion of the stem. Panel 2: Branched horsetail, detail of the bases of the branches in a whorl of branches.
Branching in horsetails (Equisteum). In horsetails (Equisetum), lateral branches alternate with the leaves, which are fused around the stem in a sheath. The tips of individual leaves can usually be observed as teeth (triangular points) on the sheath. Left: Marsh horsetail (Equisetum palustre), showing whorls of elongating branches around the stem; one leaf sheath can be observed, with dark teeth (leaf tips). Right: Detail of a whorl of branches on branched horsetail (Equisetum ramosissimum). Credits: Equisetum palustre (AnRo0002, via Wikimedia Commons, CC0 1.0/Public Domain Dedication); Equisetum ramosissimum (Stefan.Iefnaer, via Wikimedia Commons, CC-BY-SA 4.0).

Adventitious branching

Adventitious branching is branching that does not occur via the normal process of branching for a given plant. In general terms, adventitious structures are structures that develop in unexpected places. Note that "unexpected" means unexpected from the perspective of the organization of the plant embryo and standard plant body plan. Adventitious structures are rather common in plants, and, in fact, can be an essential part of the development of some types of plants. For example, adventitious roots (stem-borne roots) replace the primary root (the root the develops from the embryonic root) in many pteridophytes and monocots as the plants transition from embryo to mature forms.

For an apically branching plant, adventitious branches are branches that do not develop by division of the shoot apex, but arise elsewhere. For plants with axillary branching, adventitious branches grow from buds that develop in a region away from the leaf axil (or former leaf axil, if the leaf has been shed). Cycads, which typically branch apically, can form adventitious lateral branches. In this case, suckers (also called bulbils, offsets, or pups) may form on the sides of stems, from tissue in the leaf bases.


2-Panel photo figure. Panel 2. Pups (small buds with pinnately compound leaves) on the side of a sago palm trunk. Panel 2: Pup (large bud with leaf petioles and catatphylls) at the base of a queen sago trunk.
Cycad pups. Cycad pups are suckers (adventitious shoots) that develop on the bases or sides of cycads stems. If allowed to grow, they may develop into branches. Left: Pups on the side of a stem of a large sago palm (Cycas revoluta); the white arrow indicates one of the pups. Right. Pup on the base of a queen sago (Cycas circinalis) stem. Credit: E.J. Hermsen (DEAL).

Monopodial & sympodial growth

Plants with lateral branching may exhibit either monopodial or sympodial growth. In monopodial growth (Greek, monos = one + Latin, podium = foot), a stem elongates via new growth produced by a single terminal bud. In sympodial growth (Greek, sym = together + Latin, podium = foot), a stem elongates via new growth produced by a successive series of lateral buds that take on the role of the terminal bud. Thus, in sympodial growth, a stem is made up of growth produced by multiple, separate buds in a sequence.

Monopodial growth

In monopodial growth, a stem elongates from a single, terminal shoot apex. Lateral branches develop from lateral or axillary buds.


Two diagrams showing monopodial growth. Diagram 1: Stem with terminal and lateral buds; arrows show direction of growth. Diagram 2. Stems with new terminal growth from terminal bud and lateral branches from lateral buds.
Monopodial growth. The diagrams above illustrate monopodial growth. Left: Stem with terminal bud (shoot apex of the main shoot) and lateral buds (=axillary buds); the purple arrows indicate the direction of growth of each bud. Right: The same stem with new growth. Growth of the main stem is from the terminal bud, whereas lateral buds give rise to lateral branches. Credit: E.J. Hermsen (DEAL), after figure 9.5 in Simpson (2010).

Sympodial growth

In sympodial growth, a stem is made up of growth from more than one bud. Successive lateral buds take over the role of the shoot apex (terminal bud), adding to the growth of the stem sequentially.

Terminology note: A lateral bud that takes over the role of a terminal bud to produce what appears to be a single continuous stem is sometimes called a false terminal bud or pseudoterminal bud (Greek, pseudēs = false). In the diagrams on this page, a bud is labelled a terminal bud when it serves the role of a terminal bud, regardless of its original developmental position. The distinction between true and false terminal buds can be important in woody plant identification.


Diagram of sympodial growth producing a branch. In each stage of growth, the apical bud is replaced by a lateral bud, which continues the growth of the branch.
Sympodial growth. In sympodial growth, a single stem is elongated by growth by successive buds. In the diagram above, the terminal bud ceases growth after an interval of time (for example, a season) and is replaced by a lateral bud, which serves as a new terminal bud and adds length to the same stem for the next interval of time. Credit: Diagram by E.J. Hermsen (DEAL), after fig. 8b in Donoghue (1981).

A simple type of sympodial growth occurs when a single stem is produced by a series of lateral buds that take on the role of the terminal bud one after another in succession. Some plants that grow from rhizomes have this type of growth. A rhizome is a horizontally growing underground stem. In sympodial growth of a rhizome, a terminal bud adds length to the rhizome for awhile, before deflecting its growth upward and producing an aerial (above-ground, often upright) shoot. Growth of the rhizome is then continued by a lateral bud, which takes over the role of the terminal bud.

4 Part diagram showing growth of a monochasium. 1. Horizontally oriented stem with an upright axis bearing a reproductive structure; growth of the horizontal axis continues by a terminal bud; Part 2: The horizontal stem is longer and the terminal bud changes its direction of growth to turn upwards; a lateral bud is next to the terminal bud. Part 3: The original terminal bud has produced a reproductive structure and the lateral bud continues growth of the horizontal stem. Part 4: The terminal bud changes direction of growth to turn upwards, and a new lateral bud will take over growth of the horizontal stem.
Sympodial growth of a horizontally oriented rhizome or branch. In the diagrams above, growth of a horizontally oriented stem is continued by a succession of lateral buds that take over the role of the shoot apex (terminal bud). Growth of the stem in continued by only one bud at a time. Credit: E.J. Hermsen (DEAL), after fig. 11 in Donoghue (1981).

In some shrubs, sympodial growth produces plagiotropic (Greek, plagios + tropos = oblique turning) branches, or branches that grow roughly parallel to the ground. A terminal bud may add length to a plagiotropic branch for awhile, before turning upwards to produce a group of flowers. Growth of the branch then resumes from one of the lateral buds, which takes over the role of the terminal bud. This type of sympodial growth thus produces a horizontally oriented stem with short, upright branches bearing reproductive structures on its upper side.

Photo of a herbarium specimen of hobblebush showing sympodial growth of branches; each segment ends when the terminal bud turns upward to produce flowers, with growth of the branch continued by a lateral bud.
Sympodial growth in hobblebush. Hobblebush (Viburnum lantanoides, an angiosperm) has plagiotropic (horizontal) branches with sympodial growth. The horizontally growing branches are elongated by successive lateral buds. Each interval where a new bud takes over is marked by an upright reproductive axis (the short stems with leaves and usually flowers) and is slightly curved. On the upper branch, the arrows indicate each place where a new bud took over the role of the terminal bud; the growth intervals are numbered from oldest (1) to youngest (3). Credit: Viburnum lantanoides, NYBG 02461839 (New York Botanical, via GBIF, CC BY 4.0). Image modified from original.

In another type of sympodial growth, the terminal bud is replaced by two lateral buds every time it ceases growth; thus, a branch is replaced by two branches at each successive interval of the sympodium. For example, in some plants, a terminal bud will add length to a branch for awhile, then either abort (in other words, cease to function) or produce a reproductive structure. Growth will resume from two lateral buds, producing two equal branches.

3-Part diagram of the growth of a dichasium. Part 1. Stem with aborted terminal bud and two lateral buds, one on either side. Part 2: The 2 lateral buds have produced two branches and abort; growth is taken over by lateral bud pairs near each aborted terminal bud. Part 3. Each lateral bud pair has produced new branches, and they have aborted; new lateral bud pairs are ready to take over growth.
Sympodial growth by lateral bud pairs. In the diagrams above, growth of a stem is continued by a succession of pairs of lateral buds that take over the role of the terminal bud. Thus, growth of the stem is continued by two branches at a time. Aborted buds in each diagram are indicated by a black "X." Credit: E.J. Hermsen (DEAL), after fig. 8c in Donoghue (1981).

Image
Sympodial growth by a lateral bud pair in lilac. Portion of a lilac (Syringa vulgaris) shoot showing sympodial growth. In this case, the terminal bud of a stem has aborted, with growth continued by two lateral buds (the location where this happened is indicated by the arrow). Note that this branching pattern looks similar to a dichotomy produced by apical branching. Credit: Syringa vulgaris, MHA0150658 (image by MHA Herbarium, rights held by GBS RAN, via GBIF, CC BY 4.0). Image modified from original.

Sympodial growth of angiosperm inflorescences

Sympodial growth is sometimes found in angiosperm inflorescences (groups of flowers). If sympodial growth of the inflorescence axis (the stem bearing the group of flowers) continues by one bud at a time in succession, the inflorescence is a monochasium. An example of a monochasium is the scorpioid cyme shown below. Unlike the examples of the rhizome and the plagiotropic branch illustrated above, the positions of the lateral buds that take over the role of the terminal bud in each growth interval alternate in a scorpioid cyme. Thus, the scorpioid cyme has two rows of flowers, one on either side of the sympodial inflorescence axis. (For another example, see the photograph of a forget-me-not scorpioid cyme on the Flowers page.)


2-Panel figure of scorpioid cymes. Panel 1: Drawing of branching pattern, showing that lateral buds alternate to produce two rows of flowers. Panel 2: Scorpioid cymes of alkali heliotrope, each clearly showing two rows of flowers (photos).
Scorpioid cyme, monochasium. Left: Diagram of a scorpioid cyme, showing the order of branching. A scorpioid cyme is a type of monochasium formed by sympodial growth. Right: Alkali heliotrope (Heliotropum curassavicum) showing scorpioid cymes, each with two rows of flowers. Credits: Cincinnus (Rasback, via Wikimedia Commons, CC BY-SA 3.0); Heliotropum curassavicum (sherriff_woody_pct, via iNaturalist, CC BY 4.0). Images modified from originals.

If sympodial growth of an inflorescence continues by two buds at a time, the inflorescence is a dichasium. In a dichasial cyme, each terminal bud ends in a flower, with growth continued by pairs of lateral buds that occur at the base of each flower stalk (if no stalk is present, then branches arise at the base of each flower).

2-Panel image of compound dichasial cymes. Panel 1: Diagram of a compound dichasial cyme, with each axis ending in a flower and growth taken over by pairs of lateral axes. Panel 2. Photo of a herbarium specimen of bladder campion showing dichasial cymes.
Dichasial cymes. Left: Structure of a diachasial cyme. Note that each axis ends in a flower (represented by a red circle), with growth of the inflorescence continued by pairs of lateral buds that occur at the base of each flower stalk. The order of branching is indicated by the number above or next to each flower. Right: Dichasial cymes in bladder campion (Silene vulgaris); the dichasial cyme shown here only has three orders of branching (see whether you can identify them). For an example of a dichasial cyme on a live plant, see the Flowers page. Credits: Dichasium (supermartl, via Wikimedia Commons, Public Domain); Silene vulgaris subsp. macrocarpa (Botanic Garden and Botanical Museum Berlin, via GBIF, CC BY-SA 3.0 DE). Images modified from originals.

Root branching

Like shoots, roots can branch apically or laterally. While apical branching in roots is similar to apical branching in stems, lateral branching is distinct. Notably, roots have originated at least twice in vascular plants, separately in the lycophytes and euphyllophytes.

Root apical branching (dichotomous branching)

Apical or dichotomous branching in roots is similar to apical branching in stems. Dichotomizing roots are found in the lycophytes and are sometimes considered a synapomorphy for that group; however, recent research indicates that apical root branching occurred in some extinct euphyllophytes, even if it is not found in modern euphyllophytes (living ferns, horsetails, and seed plants). Lycophyte roots are sometimes also called dichopodial (Greek, dicho- + Latin, podium = foot).

Note: Many plants with apical stem branching lack true roots, including the extinct protracheophytes and early vascular plants (like Agalophyton,  illustrated above on this page), as well as the living whisk ferns (Psilotum). These plants are anchored with rhizoids, which are simple thread-like structures. Roots, in contrast, are organs made up of concentric layers of tissues.


3-Part diagram showing apical branching in a root. Part 1: Single root axis with central vascular tissue. Part two: Root tip and internal vascular tissue begin to fork. Part 3. Lateral two branches develop further, forming an equal dichotomy.
Apical root branching. The diagrams above show the sequence of apical branching in a root. The root apex divides to produce two equal branches. The root in shown in longitudinal section. The yellow lines represent the central cylinder of vascular tissue within the root. Credit: E.J. Hermsen (DEAL), after fig. 1e in Hetherington et al. (2020).

Photo of shining firmoss (a lycophyte), showing dichotomizing roots on one of the plants.
Lycophyte root branching. Northern firmoss (Huperzia selago). The plant on the right has dichotomously branched roots. The arrow indicates the position of one of the dichotomies. Credit: Huperzia selago, MHNT.BOT.2005.0.999 (Didier Descouens, via Wikimedia Commons, CC BY-SA 4.0). Image modified from original.

Root lateral branching

In many euphyllophytes, roots are monopodial and branch laterally. Whereas shoot lateral branches arise exogenously (in other words, from lateral buds on the surface of the stem), root lateral branches arise endogenously (in other words, from within the root itself). Lateral roots begin development in a region known as the pericycle, which forms the outer sheath of the vascular cylinder (strand of vascular tissue). A lateral root must grow through the cortex and epidermis of the root from which it branches.


3-Part figure of lateral root branching. Part 1: Unbranched root with central vascular strand. Panel 2: Small lateral root primordium emerging at the edge of the vascular tissue in the main root. Panel 3: Lateral root has elongated now extends outside of the main root.
Lateral root branching. The diagrams above show the sequence of lateral branching in a root. The lateral root first arises as a primordium at the edge of the vascular tissue. It must then grown through the root cortex and break through the epidermis. The root is shown in longitudinal section. Yellow lines represent the vascular tissue within the root. Credit: E.J. Hermsen (DEAL), after fig. 1b in Hetherington et al. (2020).

Photo of a cross-section of a willow root with a lateral root (lateral root is in longitudinal section).
Lateral root. Cross section of a willow (Salix, an angiosperm) root with a lateral root branching from it (the lateral root is in longitudinal section because it is perpendicular to the main root). Unlike shoot branches, which arise from superficial buds on the sides of the stem, lateral roots originate from within the root they branch from. Credit: Salix root (Jon Houseman and Matthew Ford, via Wikimedia Commons, CC BY-SA 4.0). Image modified from original.

Selected references & further reading

Note: Free access is provided by the publisher for items marked with a green asterisk.

Academic articles & book chapters

* Banks, H.P., S. Leclercq, and F.M. Heuber. 1975. Anatomy and morphology of Psilophyton dawsonii sp. n. from the late lower Devonian of Quebec (Gaspé), and Ontario, Canada. Palaeontographica Americana 8: 77–127. Available on Biodiversity Heritage Library: https://www.biodiversitylibrary.org/page/10692435

Buys, M.H., and H.H. Hilger. 2003. Boraginaceae cymes are exclusively scorpioid and not helicoid. Taxon 52: 719–724. https://doi.org/10.2307/3647346

* Chomicki, G., M. Coiro, and S.S. Renner. 2017. Evolution and ecology of plant architecture: integrating insights from the fossil record, extant morphology, developmental genetics and phylogenies. Annals of Botany 120: 855–891. https://doi.org/10.1093/aob/mcx113

* Donoghue, M. 1981. Growth patterns of woody plants with examples from the genus Viburnum. Arnoldia 41: 2-23. PDF available from the Arnold Arboretum (Harvard): http://www.arnoldia.arboretum.harvard.edu/pdf/articles/1111.pdf

* Gola, E.M. 2014. Dichotomous branching: the plant form and integrity upon the apical meristem bifurcation. Frontiers in Plant Science. https://doi.org/10.3389/fpls.2014.00263

Hetherington, A.J., and L. Dolan. 2018. Stepwise and independent origins of roots among land plants. Nature 561: 235–238. https://doi.org/10.1038/s41586-018-0445-z Read free on PubMed (PMCID: PMC6175059): https://pubmed.ncbi.nlm.nih.gov/30135586/

Hetherington, A.J., C.M. Berry, and L. Dolan. 2020. Multiple origins of dichotomous and lateral branching during root evolution. Nature Plants 6: 454–459. https://doi.org/10.1038/s41477-020-0646-y

* Matsunaga, K.K.S., and A.M.F. Tomescu. 2016. Root evolution at the base of the lycophyte clade: insights from an Early Devonian lycophyte. Annals of Botany 117: 585–598. https://doi.org/10.1093/aob/mcw006

Stevenson, D.W. 2020. Observations on vegetative branching in cycads. International Journal of Plant Sciences 181: 564–580. https://doi.org/10.1086/708812

* Stopes, M.C. 1910. Adventitious budding and branching in Cycas. New Phytologist 9: 235–241. https://doi.org/10.1111/j.1469-8137.1910.tb05571.x

* Vasco, A., R.C. Moran, and B.A. Ambrose. 2013. The evolution, morphology, and development of fern leaves. Frontiers in Plant Science 4: 345. https://doi.org/10.3389/fpls.2013.00345

Books & textbooks

Bierhorst, D.W. 1971. Morphology of vascular plants. The Macmillian Company, New York, New York.

Foster, A.S., and E.M. Gifford. 1974. Comparative Morphology of Vascular Plants, 2nd ed. W.H. Freeman and Co., San Francisco.

Simpson, M.G. 2010. Plant Systematics, 2nd ed. Academic Press, Burlington, Massachusetts.

Taylor, T.N., E.L. Taylor, and M. Krings. 2009. Paleobotany, the Biology and Evolution of Fossil Plants, 2nd ed. Academic Press.

Blogs, magazines, websites

* Aiello, A.S., and M.S. Dosmann. 2019. Déjà vu viburnums: A world away but close to home. Arnoldia 76: 14–25. https://arboretum.harvard.edu/stories/deja-vu-viburnums-a-world-away-but-close-to-home/

* Hetherington, S. 2020. Unearthing the complex evolutionary origins of root branching. Nature Research Ecology & Evolution Community. https://natureecoevocommunity.nature.com/posts/65945-unearthing-the-complex-evolutionary-origins-of-root-branching

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First released 13 January 2021; last updated 28 January 2021.