Plant cells             Multicellularity               Modularity

Plant bodies - building plants from cells and modules

The flowering plant body

When one first examines the patterns and morphology of plants in detail, the diversity of shapes and forms can be bewildering! Things make more sense once one understands a bit about plant development. Plants grow from meristems, localised regions where cell division occurs. The cells produce enlarge and mature, differentiating as they do so into the full variety of plant cell types needed by the growing organ. Apical meristems occur in the tips of growing shoots and roots and cause these organs to elongate. Lateral meristems may be involved where the plant continues to grow thicker, such as the cylinder of cambial cells between the inner bark and wood of a tree or shrub.

Many of the specialised structures that plants produce are modifications of the basic structures. Flowers are compressed (shortened shoots) on which the whorls of leaves develop instead into sepals, petals, carpels and stamens. Flower clusters may form where an entire portion of the shoot system, complete with all its branches, forms a cluster of flowers, which may, for example, be arranged on a central spike or on a single platform resembling a single flower, as in Asteraceae (Compositae). For example, the 'flower' of a daisy is in fact a compressed shoot system made up of a number of flowers and reduced leaves (ligules) with the flowers on the margin being modified to resemble petals.

It becomes apparent that plants are actually made-up of repeated branching units or modules, which may be more-or-less modified. The typical angiosperm body consists of the shoot and root systems. The shoot system consists of one or more main axes bearing side-branches at regular intervals on modified sections of stem called nodes. The segments of stem between nodes being called the internodes. The side-branches develop from buds in the axils of leaves, the axillary buds. The shoot grows as new cells form behind the apical meristem in the shoot tip or apex. The leaves may alternate from left and right, sometimes forming a spiral or helix around the stem or branch axis; or they may occur in pairs opposite one-another at the same level on either side of the axis. The branching may adopt a three-dimensional pattern with branches and leaves surrounding the main axis in circles or spirals called whorls, or the plant may show some degree of planation or tendency to branch in a two-dimensional plane, assuming a flattened form. Typically one shoot apical meristem, perhaps the main central stem, will assume dominance and other side branches will only grow to a lesser degree or even remain as dormant buds.

Above: the generalised angiosperm (flowering plant) body. This diagram shows the baulk-plan of a flowering plant. Based on (redrawn and simplified) a diagram in Esau, Anatomy of the Seed Plant 2nd edition, Wiley. (One of the best botany books ever written).

Shoots may also grow horizontally (plagiotropic growth) perhaps producing a creeping stem, such as the creeping shoots of ivy that snake along the woodland floor until they find a tree or other support to climb up. horizontally underground stems, or rhizomes, may act as storage organs and give off vertical branches at intervals which grow above ground. Alternatively shoots may grow vertically (orthotropic growth). Things are not so simple, a branch may grow horizontally along one portion of its length and vertically along another. Such a branch commences growth in one direction and at some point secondarily changes direction. Light and gravity are important stimuli sensed by the plant to help it determine its growth form or habit. Some shoots may possess a joint (pulvinus) about which they bend. A tree that falls over but remains rooted may change direction of growth, causing new growth at the tip to bend upwards vertically (or one of its branches, now vertical, may become the dominant shoot and form a secondary stem). Shoots may also grow vertically initially, but curve over under their own weight. In Prunus (e.g. plum trees) the shoot apex grows horizontally but then later curves over so that the basal or proximal portion (oldest part of the shoot) forms a vertical (or slightly curved) stem whilst the tip of the stem grows lies more-or-less horizontal. In Prunus the branches also grow more-or-less horizontally. (This growth habit is described by the model of Troll). Plane trees (Platanus) also grow in this way and each largely horizontal branch may arch down and form roots where it contacts the soil, allowing a new stem to grow upwards at this point ('self-layering' a form of asexual reproduction).

Not all plants belong to the flowering plants or angiosperms, conifers produce cones with naked seeds instead of flowers and fruit that completely enclose the seeds. Ferns, club mosses, horsetails and bryophytes (such as mosses and liverworts) are examples of spore-producing plants that also produce no flowers. However, angiosperms are the most evolved of the plant groups and conifers are very similar in many respects, so we shall consider the angiosperm first. Angiosperms include herbaceous plants, such as daffodils and dandelions, grasses, bamboos and palms, and woody plants like hawthorn shrubs/small trees and large trees like the oak. The gymnosperms include conifers and other woody trees that have no fruit, such as yew trees, Scot's pine and sequoia.

Plants are modular organisms

The angiosperm plant body is divided into the shoot system, which constitute the parts that are usually above ground, and the root system which is usually below ground. Both root and shoot systems are modular - that is they are made from repeating modules fitted together. A module is a repeating unit, for the shoot system, a module consists of a branching unit - typically a branch, leaf and axillary bud in the join between leaf and branch. The plant grows by successively adding more modules, and modules to modules. Thus, a bud gives rise to a new shoot, such as a twig, with its own leaves, while the older modules grow thicker. These modules are not put together haphazardly, but in specific patterns - the so-called branching pattern. Each module has all it needs to become a whole new organism - cut a shoot from a tree and plant it and it may grow roots and become anew tree. Willow trees are particularly good at this, and can regenerate from a single twig. Indeed, willows use this strategy deliberately to reproduce - they prefer to grow near to water and they shed twigs into the water, get carried downstream and if they root in the bank then they may grow into new trees. The crack willow (Salix fragilis) is so-called because its fragile wood tends to split under its own weight, but this helps the tree disperse itself as twigs and branches fall into the water.A leaf, however, will not normally grow into a plant (except in special artificial culture conditions) since it is not a whole module, but only part of one.

Branching patterns

Each flowering plants conforms to one of about 24 branching patterns found among the angiosperms. Growth may be determinate, with no branches except in the flower head which tops the single straight stem. Determinate growth is so-called because it is genetically predetermined that the plant or shoot will grow so long and then stop, ending in a flower. The inflorescence of a foxglove is one example. Growth may be indeterminate, continuing more or less continuously as existing modules continue to elongate or new modules are added (though eventually reaching a variable limit). In monopodial growth, the stem is constructed of a single straight shoot, bearing side-branches, with the single axis (monopodium) developing from a single apical bud that continues to grow, continuously or periodically. The coconut palm (Cocos nucifera) consists of indeterminate monopodial growth. The talipot palm (Corypha utan) has a determinate monopodium, with the single axis ending in an inflorescence (flower bearing shoots) at which point the apical bud ceases to grow any further. Most conifers, e.g. fir trees, are also monopodial, with branches radiating in whorls from a central axis derived from the same terminal bud which continues to grow, producing the classic conical Christmas-tree shape. This shape is good for shedding snow. Prunus trees (such as plum trees) have monopodial trunks.

The trees with which most people are familiar, such as oak trees and maple trees, exhibit sympodial growth. Sympodial plants are the  truly modular plants, with the stem consisting of a series of modules stacked one on top of the other, with each terminal (apical) bud ending in a flower at some stage in growth and the main stem or branch continuing its growth with the extension of the previous modules axillary bud, forming a new module in which again the apical bud ends as a flower whilst the axillary bud continues growth. Examples of this indeterminate sympodial growth include the oak tree and the maple (broad-leaved trees). The sympodial plant may  still appear to have a single straight axis (formed from a series of modules), however, but close analysis reveals the history of its growth.

Sometimes, the trunk may be monopodial and the branches sympodial, as in Sterculia species ('tropical chestnuts').

Below the European Oak, Quercus robur. The trunk and branches are both sympodial,helping to give the trees an undulating serpentine appearance. (Click image for wallpaper size!).

There are additional ways to describe the branching patterns of plants. One of these is the branching or bifurcation ratio, BR. BR is the number of distal branches divided by the  number of proximal branches. for example, in shade-adapted Fraxinus americana (American Ash) the stem and each branch terminate in two branches, on average, giving a BR of 2:1. In contrast, sun-adapted Fraxinus americana have a BR of 9:1, that is the main stem will put our 9 lateral branches, on average, giving a more 'fir-tree' like appearance. Work on shrubs has shown that only three orders of branching represent the branching pattern of the entire shrub, since the pattern repeats. In other words, one need only consider the smallest (primary) twigs, their parent twigs and the branches the parent twigs are attached to, higher order (larger) branches will reflect the same pattern 9in fractal fashion: zooming in causes the pattern to repeat).

According to one study, sun or shade made little difference to the BR of Quercus rubra (Red Oak) but the first order terminal shoots were elongated (by about 50%) and the average branch angle (the angle between daughter branches at the apex of the parent branch) increased from 46 degrees in the sun to 77 degrees in the shade. Thus, shade-adapted plants had more spreading branches which were elongated.

Above: The simplest branching pattern is dichotomous branching (left) in which the growing tip forks into two, more-or-less equal branches, each of which continues growth with repeated forking a certain number of times (in this example there are three orders of branch plus the main stem). In true dichotomous branching, the growing tip meristem itself splits into two meristems. This kind of growth is seen in many seaweeds, liverworts and only a few flowering plants, such as certain cacti and palm trees. Dichotomous branching is rare in flowering plants, and when it does occur it may involve the growth of two lateral shoots on either side of the central shoot whose growth is suppressed, this is called false-dichotomy (pseudo-dichotomy).

Above: Sympodial branching is similar to pseudo-dichotomous branching except that one branch in each fork dominates, with the dominate branch alternating (left-right-left in the example shown). The alternate shoots may grow upright initially, before leveling off, giving rise to a single sympodial trunk. This growth pattern is common in broad-leaved trees and examples include the oak tree (Quercus), Beech (Fagus) and Lime (Tilia).

Monopodial growth, above, occurs when one central axis and its terminal meristem dominate growth. This is seen in many flowering herbaceous plants, in which the central axis eventually terminates in an inflorescence (cluster of flowers) in determinate growth, as in many orchids. Some orchids, however, are sympodial.

Below: bifurcation ratio and branch order:

The order of the branches is indicated in the figure above. This system of ordering branches is also used in the study of rivers and is the Horton-Strahler system. In this system, the smallest terminal branches are order 1 and two order 1 branches converge to form an order 2 branch. If branches of different order meet then the order is not changed, so an order 1 branch meeting an order 2 branch does not change its order (in other systems it might change the order of that branch segment to 3, such a system rating the order by physical size). Essentially, we have computed branching ratio (BR) as the number of branches of a given order, divided by the number of branches of the next highest order. Alternatively, we can use the following formula for the whole plant:

${R}_{b}=\frac{N-{N}_{max}}{N-{N}_{1}}$

Where: Rb is branching ratio, N is the total number of branches of all orders, N_max is the number of branches of the highest branching order and N1 is the number of branches of first order. For example, for the tree shown above right: there are 15 branches in total (including the main stem) and 1 order 4 branch, so N_max = 1, giving us (15 - 1 = 14) 14 on the top; there are 8 first order branches, giving us (15 - 8 = 7) 7 on the bottom and thus the branching ratio = 14:7 = 2:1 (or 2) as required.

Harry Marshall Ward (1854 - 1906) in volume 5 of his Trees: a handbook of forest-botany for the woodlands and the laboratory (1909, Cambridge University Press, now in the public domain) gave some examples of a useful approach to analyzing and understanding the branching patterns of trees, some of his examples are summarized below (the embedded diagrams taken from his aforementioned work).

The saplings of many trees tend to have more perfect symmetry than mature trees (life events perturb the programmed symmetry of the tree as it grows) and are often regular and more-or-less conical/pyramidal or cylindrical. Consider first sympodial branches on a single main system (also sympodial but not obviously so) with the branches alternate and in a spiral along the stem with a wide branch angle.

The apical meristem / bud of the leader eventually ceases growth (in sympodial fashion)and further emphasis on growth is in developing long and thick sympodial branches in which some branches at each node grow and others do not, resulting in tortuous 'zig-zagging' sympodial branches. The result is the type of tree we see in mature oaks, chestnuts, walnuts and plane trees.

This time let us begin with a similar arrangement but with an acute branch angle and develop two possible growth patterns and see where they lead us.

This time we begin with the branches arranged opposite (i.e. branches on opposite sides level with one-another) and decussating (crossing-over, so that each successive pair of branches is rotated by approximately 90 degrees around the stem).

Finally, let us consider a conifer, such as a pine, with a monopodial trunk and whorls of monopodial branches as it goes through several stages of maturation.

The result is a conical or pyramidal tree in early age and an umbrella-shaped tree in old age. Such a pattern is often seen in Stone Pine also called the Umbrella Pine (Pinus pinea) and sometimes in Scots Pine (Pinus sylvestris).

Notice how these patterns involved processes of suppressing certain buds or branches and of programmed shedding of older branches (for example when overshadowed or when nutrients are prioritized to the upper branches). Branch shedding is generally a deliberate and programmed process in which the branch forms a proper abscission zone with protective corky tissue already developed over the remaining base. Branches can also be lost by accident or injury and then scar tissue will form a callus that gradually closes over the wound.

Why do trees (and other plants) branch?

A tree or shrub absorbs both light and carbon dioxide from the atmosphere. Plants these need things in order to grow. The light energy is used to convert the carbon dioxide into fuels and materials to build the plant body, in a process known as photosynthesis. (Water and minerals are also required for photosynthesis and these are generally obtained from the soil supplied by the roots). Carbon dioxide and light are absorbed by the leaves. The stem and branches serve to position the leaves high in the air, so that the plant can access the light and carbon dioxide without its neighbors stealing these resources first - taller plants will overshadow shorter plants. The question now becomes: why not have a solid green sphere instead of a branching canopy? Each leafy branch absorbs carbon dioxide from the surrounding air, leaving a zone of carbon dioxide depleted air around it. It then relies upon diffusion (the random motion of molecules like carbon dioxide) or advection (bulk air movements or wind) to bring in new supplies of carbon dioxide from the surrounding air further from the branch. If the branches are packed too close together (or if the canopy is a solid mass) then neighboring parts of the canopy will compete and some regions will not obtain sufficient carbon dioxide. In fact computer simulations (using the diffusion equation) have shown that alternating regions of low and high carbon dioxide concentration would develop around the canopy. It makes no sense for a tree to position foliage in the areas of low concentration, since such foliage will consume more fuels and materials than it produces. The solution is to break the canopy up into branches and position the branches an optimum distance apart so that they do not deplete one another's supplies of carbon dioxide. Computer simulations predict that some 20 or so different branching patterns achieve this optimum and most of these are seen in nature, but no tree species confirms to any pattern of branching that is sub-optimum.

Thus, trees branch so as to break up their canopy in such a way that maximizes their absorption of carbon dioxide and light. The final pattern of branching is both genetic (and so dependent upon tree species) but also a result of how the tree responds to its environment as it grows. Growing shoots will seek out light (and presumably carbon dioxide) and leaves will position themselves to catch the light. In some plants these movements occur as the shoot grows, but in many plants the leaves maintain some ability to move about when mature and in some species they may undergo daily movements as they follow the sun.

Leaves are also hinged - look at the end of a leaf stalk where it joins the branch and you will see a swollen region (the pulvinus) which permits movement of the leaf. The pulvinus and leafstalk allow the leaves to rustle in the breeze. This rustling movement serves to mix the air around the leaf, replenishing the carbon dioxide around the leaf, and also helps keep the leaf cool and helps it to resist high winds (a stiffer structure may more likely break). Leaves may also break up their contour, forming lobed leaves with finger-like lobes, such as in the maple - this also optimizes absorption of carbon dioxide and leaf cooling. Indeed in some plants, the 'sun leaves' at the top of the plant may have a very different shape to the 'shade leaves' near to the base of the plant, and this probably reflects the greater need of the sun leaves to keep cool. Trees such as the aspen and poplar have particularly mobile leaves and are famous for the way their leaves rustle in even the slightest breeze.

Branching Patterns in Horizontal and Vertical Shoots

As an example, Petrokas (2011) has given a detailed description of branching patterns in Wych Elms (Ulmus glabra). As a small tree that sometimes grows as a shrub, Wych Elm displays a variety of branching patterns in its vertical (orthotropic) shoots. Vertical shoots may sometimes branch near the base, forming two co-dominant axes, or several axes may be present at soil level (multi-dominant axes), each such axis being a dominant or leader axis. Alternatively, the main axis may fork or trifurcate (branch into three) near ground level with one branch becoming the dominant leader; or the stem may divide higher up or not divide at all, putting out lateral branches.

Plants are modular organisms, typically one module being added to each growing shoot each year. Even in tropical climates, with more-or-less constant conditions, most plants exhibit rhythmic growth. The lateral shoots put out each season by the elongating leaders can differ in their position upon the new segment of stem. They can also differ in their vigour of growth or extent/rate of elongation. It is important to note whether one is referring to the whole plant or a single growth module. In acrotony, the shoots are either positioned near the apex, or the apical shoots grow more, in basitony the basal shoots are given preference and in mesotony the middle shoots, as illustrated below:

In monopodial conifers these growth forms give rise to whorls of long branches (whorl branches) interspersed by smaller interwhorl branches. These forms are typical of a genus, but can differ with species. Atlas Cedar (Cedrus atlantica) is acrotonous, for example.

Additionally, further levels of branching can be described, in particular the lateral shoots branching from a parent or principle shoot (P) which is horizontal or nearly horizontal (plagiotropic) may develop asymmetrically. When the main branch (M) emerges from the underside (hypotony) and finally, if the lateral side-shoots are favored, then this is known as amphiotony. Amphitony occurs in Fir trees and Wych Elm, for example, and results in planar branches, although the side-shoots may angle upwards (amphitony-epitony) as is often the case in Wych Elm (Petrokas, 2011) or downwards (amphitony-hypotony).

Hypotony occurs in the cactus Opuntia fulgida, for example, and epitony in the Black Walnut (Juglans nigra). These terms can also be applied to leaves on the plagiotropic shoots of many plants (the leaves on orthotropic shoots tend to be arranged in symmetrical whorls). These terms can also be applied to sympodial trees, in which case we speak of secondary acrotony, etc.

Castellanos et al. (2011) studied branching in Buxus vahlii (Vahl's Boxwood). The diagram below is based on their work: on the left is a young juvenile tree, less than 1m tall, and on the right a mature tree about 5m tall. Note that the branching pattern is sympodial with axilary buds giving rise to the next module in the series. The lower branch of the mature tree is a later addition, produced in a process called reiteration. This occurs either in favourable conditions or in response to damage and involves the activation of a dormant (epicormic) bud which repeats or reiterates the growth form of the entire parent plant on a smaller scale. It is important to realise that the final form of the tree depends much on environmental factors, in addition to the underlying inherent branching algorithm which is essentially genetically determined.

In senescent trees some of the axes begin to die, in the case of Buxus from the top down, and reiteration occurs on some of the branches and may also occur on the main stem as dormant buds become activated to help compensate for the loss, which of cause eventually wins and becomes total.

Branching of the Inflorescence

The inflorescence is a modified and specialized shoots, or parts of shoots, bearing flowers. Since their main function is to present flowers to insect pollinators and/or the wind or water and to present fruit for dispersal, the conditions on acquiring light and carbon dioxide for photosynthesis are relaxed and a considerable variety of branching patterns may result, but the basics modular patterns are similar between the inflorescence and vegetative shoot and much of the terminology applies to both, but branching patterns are more readily apparent in the more compact shoots of the inflorescence and they are useful taxonomic characters.

Racemose branching occurs when there is a main axis that grows as much or more than the primary branches and the primary branches grow more than the secondary branches. A true main axis (monopodium) is found throughout and we have monopodial branching as found in the vegetative shoots of pine trees in which we have a vertical main stem and whorls of horizontal branches producing a more-or-less pyramidal outline. In Cypress the main lateral branches grow erect and may be as long as the main axis, producing an ovoid or spherical crown.

When an inflorescence exhibits racemose branching, several main types can be found. In the raceme, stalked flowers are borne on the main monopodium and flower stalks (pedicels) more-or-less all the same length. This is characteristic of many plants such as Foxglove, Lily of the Valley, Hyacinth, Black and Red Currants and Linaria vulgaris (Common Toadflax) below:

Above: a raceme of Linaria vulgaris (family:Plantaginaceae, formerly Scrophulariaceae).

If the lower branches elongate more, such that  the flowers are brought more-or-less to the same horizontal level (or in a dome) then the raceme is a type of corymb called a racemose corymb.

When the flowers are sessile (lacking obvious stalks) then a spike results, as found in many plants such as terrestrial orchids, broomrapes, Verbena, Mullein and Plantago (Plantain) shown below:

Above and below: Spikes of Plantago lanceolata (Ribwort Plantain, family Plantaginaceae). Note the furrowed inflorescence stalks are a characteristic of this species.Note also that the flowers open acropetally, i.e. from the base of the spike to the tip.

The catkins of many wind-pollinated temperate hardwood trees such as Poplar and Willow are pendant spikes containing flowers of one sex only, whilst many catkins are spikelike (but in fact each scaly bract encloses more than one flower so these are not true spikes) such as chestnut, Alder, Oak, Birch and Hornbeam.

Below: in Arum (family: Araceae, shown here is Arum maculatum) the spike is thickened and succulent and termed a spadix (shielded by a modified bract called the spathe).

If the lateral branches on the main axis are themselves branched, with each branch ending in a flower, then we have a panicle: a compound raceme or raceme bearing racemes: a main axis bearing branches which are themselves racemes. A panicle can also refer to branched inflorescences in which each branch is a spike, but some botanists keep the panicle as a compound raceme distinct from the compound spike (spike of spikes) as typical of grasses.

In an umbel, the main axis bears a whorl of lateral branches which grow more-or-less to the same length and end in a flower. Often umbels are compound - consisting of an umbel of little umbels (umbellules). These structures are characteristic of the Apiaceae family, such as wild carrot (Daucus carota) below:

An umbel superficially resembles a corymb, except in an umbel the flowers appear to emerge from the same level on the main axis.

If the flowers are sessile (stalkless) and attached directly to the flattened or expanded tip (receptacle) of the main axis then we have a capitulum or flower head. Often the capitulum itself resembles a single flower, as in daisies, dandelions and thistles (family Asteraceae) and related plants such as this Bristly Oxtongue (Picris echioides) below:

Note the numerous small central yellow flowers or florets making up the capitulum and the several rings of peripheral florets with petals extended outwards (each ending in 5 teeth). Think of this as like the disc of the sun with radiating rays of light.

The capitulum contains a central disc containing disc florets. These disc florets are often tubular florets in which the petals (usually 5, sometimes 4) are fused to form a corolla tube. Disc florets may be ligulate florets rather than tubular, in which case the corollas extend into 'tongue-shaped' structures called ligules (ligulate = 'tongue-shaped') which often, but not always involves all 5 petals to form a tongue or strap-shaped structure with 5 teeth at the apex indicating fusion of the 5 petals that make up the ancestral flower. Sometimes only 3 of the 5 petals in the corolla tube extend outwards to form the ligule, in which case it will end in 3 teeth.

The peripheral florets may also be tubular and resemble the inner florets, in which case all the florets are disc-florets, or they may have ligules extended into rays (like the rays of the Sun or a star extending from the disc) and are then referred to as ray-florets. The ligule of ray-florets often, but not always, contains just 3 of the 5 petals (and so has 3 teeth at its tip and is sometimes not referred to as a 'ligule' as some authors reserve this term for ligulate disc florets only). Rays are often formed only by the outermost circle of florets. Where the peripheral florets are not clearly ligulate but resemble elongated ray-like tubular florets, the term pseudoray is sometimes used.

Some botanists are very pedantic about this terminology and may have a different usage. When there is doubt, I prefer to stick to the literal meaning of descriptive terms: 'ligule' refers to a tongue-shaped corolla (having 3 or 5 lobes in the extension does not change this descriptive fact); 'ray' refers to peripheral florets with corollas extending outwards radially; 'tubular' refers to florets with symmetric corollas and 'disc' refers to florets that do not significantly extend radially to any obvious extent.

Cymose branching is an alternative to racemose branching. Whereas the latter contains a dominant monopodium, cymose branching is a pattern in which the main axis grows less strongly than the branches (which themselves grow less strongly than the secondary branches they bear).

One or several branches of the same order may continue dominant growth, producing three basic types of cymose branching:

1) If only one branch of each order is dominant the inflorescence is a monochasium (monochasial cyme). If the branches alternate (zig-zag) then the apparent main axis will be a sympodium. The primary axis may cease growth at its apical meristem altogether, as in Willow (Salix) and Lime (Tilia) trees.

2) If two lateral branches of the same order continue the branching pattern in opposite directions then a dichasium (dichasial cyme) results.

3) If more than two branches of the same order continue branching then a pleiochasium results. The multiple branches may all radiate upwards at an angle and may be arranged in whorls, as in the inflorescence of Euphorbia amygdaloides (Wood Spurge, family Euphorbiaceae) below:

Below: a dichasium (dichasial cyme), the numbers refer to shoot axis order (1 is the primary stem, 2 the primary branches, 3 the secondary branches, etc.). The arcs represent bracts (modified leaves), with each branch derived from an axiliary bud. Growth of the branches may of course distort the final pattern from the simple template shown here (in plan view):

Below: when only one branch on one side develops, then a monochasium (monochasial cyme) results and several basic patterns are possible, including the development of a sympodium. Below: when the developing branch is always on the same side (either the left or right) then a spiral-like branching pattern called a bostryx results:

Above: a bostryx (in plan view). A type of helicoid cyme. E.g. Hypericum.

Above: when all the branches are in the same vertical plane a drepanium results (shown in profile view). Circles represent terminal flowers. A type of helicoid cyme.

Below:when the developing branch alternates regularly left then right, a cincinnus results:

Above: a cincinnus in plan view. A type of scorpioid cyme.

Below: Echium vulgare - inflorescence is a spike of scorpioid cymes (most flowers in each cyme are still buds in this specimen):

Above: when the branches alternate in the same vertical plane a rhipidium results. Circles represent terminal flowers. A type of scorpioid cyme.

A verticillaster is a dichasial cyme in which some of the branch nodes become monochasial (bearing just a single flower) resulting in the appearance of a whorl, which is actually a pseudowhorl and is characteristic of the Lamiaceae in which a spike bears verticillasters, each verticillaster accompanied by a pair of leaf-like bracts:

For example in Lamiastrum galeobdolon (Yellow Archangel, family: Lamiaceae):

Another example of verticillasters - Lamium album (White Archangel, family Lamiaceae):

References

Barthelemy, D. and Y. Caraglio, 2007. Plant architecture: a dynamic, multilevel and comprehensive approach to plant form, structure and ontogeny. Ann. bot. 99: 375-407.

Castellanos, C.; D.A. Kolterman and H.F.M. Vester, 2011. Architectural analysis of Buxus vahlii Baill. (Buxaceae) in two different environments in Puerto Rico. Adansonia ser. 3, 33(1): 71-80.

Courbet, F.; J.-C. Herve; E.K. Klein and F. Colin, 2010. Diameter and death of whorl and interwhorl branches in Atlas cedar (Cedrus atlantica Manetti): a model accounting for acrotony. Ann. for. sci. 69: 125-138.

Courbet, F.; S. Sabatier and Y. Guedon, 2007. Predicting the vertical location of branches along Atlas cedar stem (Cedrus atlantica Manetti) in relation to annual shoot length. Ann. for. Sci. 64: 707-718.

Petrokas, R. 2011. Height growth and its relation to the branching habits of Wych Elm (Ulmus glabra Hudson) in Lithuania. Baltic Forestry 17(1): 83-90.

Canopy

Leaves and photosynthesis

Flowers

Epiphytes and Climbers

Tree trunks, wood and branches

Wood and bark

Stems

Stem growth

Roots and water transport

Leaf litter and deadwood

Woodland

Multicellularity

Plant cells

Plant cell types

Plant biomechanics

Article updated:

22 Feb 2014
8 Oct 2018
16 Aug 2021