A leaf is an organ of a vascular plant and is the principal lateral appendage of the stem. The leaves and stem together form the shoot. Leaves are collectively referred to as foliage, as in "autumn foliage".
Diagram of a simple leaf.
Midvein (Primary vein)
Although leaves can be seen in many different shapes, sizes and
textures, typically a leaf is a thin, dorsiventrally flattened organ,
borne above ground and specialized for photosynthesis. In most leaves,
the primary photosynthetic tissue, the palisade mesophyll, is located
on the upper side of the blade or lamina of the leaf but in some
species, including the mature foliage of Eucalyptus, palisade
mesophyll is present on both sides and the leaves are said to be
isobilateral. Most leaves have distinctive upper surface (adaxial) and
lower surface (abaxial) that differ in colour, hairiness, the number
of stomata (pores that intake and output gases), epicuticular wax
amount and structure and other features.
Broad, flat leaves with complex venation are known as megaphylls and
the species that bear them, the majority, as broad-leaved or
megaphyllous plants. In others, such as the clubmosses, with different
evolutionary origins, the leaves are simple, with only a single vein
and are known as microphylls.
Some leaves, such as bulb scales are not above ground, and in many
aquatic species the leaves are submerged in water.
1 General characteristics 2 Morphology (large-scale features)
2.1 Basic leaf types 2.2 Arrangement on the stem 2.3 Divisions of the blade 2.4 Characteristics of the petiole 2.5 Veins 2.6 Morphology changes within a single plant
3 Anatomy (medium and small scale)
3.1 Medium-scale features 3.2 Small-scale features 3.3 Major leaf tissues
3.3.1 Epidermis 3.3.2 Mesophyll 3.3.3 Vascular tissue
5.1 Biomechanics 5.2 Interactions with other organisms 5.3 Seasonal leaf loss
6 Evolutionary adaptation 7 Terminology
7.1 Shape 7.2 Edge (margin) 7.3 Apex (tip) 7.4 Base 7.5 Surface 7.6 Hairiness 7.7 Timing 7.8 Venation
126.96.36.199 Hickey system 188.8.131.52 Other systems
7.8.2 Other descriptive terms
8 See also 9 References 10 Bibliography
10.1 Books and chapters 10.2 Articles and theses 10.3 Websites
11 External links
3D rendering of a computed tomography scan of a leaf
Leaves are the most important organs of most vascular plants. Since
plants are autotrophic, they do not need food from other living things
to survive but instead use carbon dioxide, water and light energy, to
create their own organic matter by photosynthesis of simple sugars,
such as glucose and sucrose. These are then further processed by
chemical synthesis into more complex organic molecules such as
cellulose, the basic structural material in plant cell walls. The
plant must therefore bring these three ingredients together in the
leaf for photosynthesis to take place. The leaves draw water from the
ground in the transpiration stream through a vascular conducting
system known as xylem and obtain carbon dioxide from the atmosphere by
diffusion through openings called stomata in the outer covering layer
of the leaf (epidermis), while leaves are orientated to maximise their
exposure to sunlight. Once sugar has been synthesized, it needs to be
transported to areas of active growth such as the plant shoots and
roots. Vascular plants transport sucrose in a special tissue called
the phloem. The phloem and xylem are parallel to each other but the
transport of materials is usually in opposite directions. Within the
leaf these vascular systems branch (ramify) to form veins which supply
as much as the leaf as possible, ensuring that cells carrying out
photosynthesis are close to the transportation system.
Typically leaves are broad, flat and thin (dorsiventrally flattened),
thereby maximising the surface area directly exposed to light and
enabling the light to penetrate the tissues and reach the
chloroplasts, thus promoting photosynthesis. They are arranged on the
plant so as to expose their surfaces to light as efficiently as
possible without shading each other, but there are many exceptions and
complications. For instance plants adapted to windy conditions may
have pendent leaves, such as in many willows and eucalyptss. The flat,
or laminar, shape also maximises thermal contact with the surrounding
air, promoting cooling. Functionally, in addition to photosynthesis
the leaf is the principal site of transpiration and guttation.
Many gymnosperms have thin needle-like or scale-like leaves that can
be advantageous in cold climates with frequent snow and frost.
These are interpreted as reduced from megaphyllous leaves of their
Vein skeleton of a leaf. Veins contain lignin that make them harder to degrade for microorganisms.
The internal organisation of most kinds of leaves has evolved to maximise exposure of the photosynthetic organelles, the chloroplasts, to light and to increase the absorption of carbon dioxide while at the same time controlling water loss. Their surfaces are waterproofed by the plant cuticle and gas exchange between the mesophyll cells and the atmosphere is controlled by minute openings called stomata, about 10 μm which open or close to regulate the rate exchange of carbon dioxide, oxygen, and water vapour into and out of the internal intercellular space system. Stomatal opening is controlled by the turgor pressure in a pair of guard cells that surround the stomatal aperture. In any square centimeter of a plant leaf there may be from 1,000 to 100,000 stomata.
Near the ground these
The shape and structure of leaves vary considerably from species to species of plant, depending largely on their adaptation to climate and available light, but also to other factors such as grazing animals (such as deer), available nutrients, and ecological competition from other plants. Considerable changes in leaf type occur within species too, for example as a plant matures; as a case in point Eucalyptus species commonly have isobilateral, pendent leaves when mature and dominating their neighbours; however, such trees tend to have erect or horizontal dorsiventral leaves as seedlings, when their growth is limited by the available light. Other factors include the need to balance water loss at high temperature and low humidity against the need to absorb atmospheric carbon dioxide. In most plants leaves also are the primary organs responsible for transpiration and guttation (beads of fluid forming at leaf margins). Leaves can also store food and water, and are modified accordingly to meet these functions, for example in the leaves of succulent plants and in bulb scales. The concentration of photosynthetic structures in leaves requires that they be richer in protein, minerals, and sugars than, say, woody stem tissues. Accordingly, leaves are prominent in the diet of many animals.
A leaf shed in autumn.
Correspondingly, leaves represent heavy investment on the part of the
plants bearing them, and their retention or disposition are the
subject of elaborate strategies for dealing with pest pressures,
seasonal conditions, and protective measures such as the growth of
thorns and the production of phytoliths, lignins, tannins and poisons.
Translucent glands in
External leaf characteristics, such as shape, margin, hairs, the petiole, and the presence of stipules and glands, are frequently important for identifying plants to family, genus or species levels, and botanists have developed a rich terminology for describing leaf characteristics. Leaves almost always have determinate growth. They grow to a specific pattern and shape and then stop. Other plant parts like stems or roots have non-determinate growth, and will usually continue to grow as long as they have the resources to do so. The type of leaf is usually characteristic of a species (monomorphic), although some species produce more than one type of leaf (dimorphic or polymorphic). The longest leaves are those of the Raffia palm, R. regalis which may be up to 25 m (82 ft) long and 3 m (9.8 ft) wide. The terminology associated with the description of leaf morphology is presented, in illustrated form, at Wikibooks.
Prostrate leaves in Crossyne guttata
Where leaves are basal, and lie on the ground, they are referred to as prostrate. Basic leaf types
Leaves of the White Spruce (Picea glauca) are needle-shaped and their arrangement is spiral
Ferns have fronds
Arrangement on the stem Main article: Phyllotaxis Different terms are usually used to describe the arrangement of leaves on the stem (phyllotaxis):
The leaves on this plant are arranged in pairs opposite one another, with successive pairs at right angles to each other (decussate) along the red stem. Note the developing buds in the axils of these leaves.
One leaf, branch, or flower part attaches at each point or node on the
stem, and leaves alternate direction, to a greater or lesser degree,
along the stem.
Arising from the base of the stem.
Arising from the aerial stem.
Two leaves, branches, or flower parts attach at each point or node on
As a stem grows, leaves tend to appear arranged around the stem in a way that optimizes yield of light. In essence, leaves form a helix pattern centered around the stem, either clockwise or counterclockwise, with (depending upon the species) the same angle of divergence. There is a regularity in these angles and they follow the numbers in a Fibonacci sequence: 1/2, 2/3, 3/5, 5/8, 8/13, 13/21, 21/34, 34/55, 55/89. This series tends to the golden angle, which is approximately 360° × 34/89 ≈ 137.52° ≈ 137° 30′. In the series, the numerator indicates the number of complete turns or "gyres" until a leaf arrives at the initial position and the denominator indicates the number of leaves in the arrangement. This can be demonstrated by the following:
Alternate leaves have an angle of 180° (or 1/2) 120° (or 1/3): 3 leaves in 1 circle 144° (or 2/5): 5 leaves in 2 gyres 135° (or 3/8): 8 leaves in 3 gyres.
Divisions of the blade
A leaf with laminar structure and pinnate venation
Two basic forms of leaves can be described considering the way the blade (lamina) is divided. A simple leaf has an undivided blade. However, the leaf may be dissected to form lobes, but the gaps between lobes do not reach to the main vein. A compound leaf has a fully subdivided blade, each leaflet of the blade being separated along a main or secondary vein. The leaflets may have petiolules and stipels, the equivalents of the petioles and stipules of leaves. Because each leaflet can appear to be a simple leaf, it is important to recognize where the petiole occurs to identify a compound leaf. Compound leaves are a characteristic of some families of higher plants, such as the Fabaceae. The middle vein of a compound leaf or a frond, when it is present, is called a rachis.
Leaves have the leaflets radiating from the end of the petiole, like
fingers of the palm of a hand; e.g.,
With a terminal leaflet; e.g., Fraxinus (ash).
Lacking a terminal leaflet; e.g.,
Leaves are twice divided: the leaflets are arranged along a secondary
vein that is one of several branching off the rachis. Each leaflet is
called a pinnule. The group of pinnules on each secondary vein forms a
Characteristics of the petiole
The overgrown petioles of rhubarb (Rheum rhabarbarum) are edible.
Petiolated leaves have a petiole (leaf stalk), and are said to be
Sessile (epetiolate) leaves have no petiole and the blade attaches
directly to the stem. Subpetiolate leaves are nearly petiolate or have
an extremely short petiole and may appear to be sessile.
In clasping or decurrent leaves, the blade partially surrounds the
When the leaf base completely surrounds the stem, the leaves are said
to be perfoliate, such as in Eupatorium perfoliatum.
In peltate leaves, the petiole attaches to the blade inside the blade
Free, lateral As in Hibiscus. Adnate Fused to the petiole base, as in Rosa. Ochreate Provided with ochrea, or sheath-formed stipules, as in Polygonaceae; e.g., rhubarb. Encircling the petiole base
Interpetiolar Between the petioles of two opposite leaves, as in Rubiaceae. Intrapetiolar Between the petiole and the subtending stem, as in Malpighiaceae.
Veins See also: § Venation, and § Vascular tissue
Branching veins on underside of taro leaf
The venation within the bract of a lime tree
Veins (sometimes referred to as nerves) constitute one of the more
visible leaf traits or characteristics. The veins in a leaf represent
the vascular structure of the organ, extending into the leaf via the
petiole and provide transportation of water and nutrients between leaf
and stem, and play a crucial role in the maintenance of leaf water
status and photosynthetic capacity.They also play a role in the
mechanical support of the leaf. Within the lamina of the leaf,
while some vascular plants possess only a single vein, in most this
vasculature generally divides (ramifies) according to a variety of
patterns (venation) and form cylindrical bundles, usually lying in the
median plane of the mesophyll, between the two layers of
epidermis. This pattern is often specific to taxa, and of which
angiosperms possess two main types, parallel and reticulate (net
like). In general, parallel venation is typical of monocots, while
reticulate is more typical of eudicots and magnoliids ("dicots"),
though there are many exceptions.
The vein or veins entering the leaf from the petiole are called
primary or first order veins. The veins branching from these are
secondary or second order veins. These primary and secondary veins are
considered major veins or lower order veins, though some authors
include third order. Each subsequent branching is sequentially
numbered, and these are the higher order veins, each branching being
associated with a narrower vein diameter. In parallel veined
leaves, the primary veins run parallel and equidistant to each other
for most of the length of the leaf and then converge or fuse
(anastomose) towards the apex. Usually many smaller minor veins
interconnect these primary veins, but may terminate with very fine
vein endings in the mesophyll. Minor veins are more typical of
angiosperms, which may have as many as four higher orders. In
contrast, leaves with reticulate venation there is a single (sometimes
more) primary vein in the centre of the leaf, referred to as the
midrib or costa and is continuous with the vasculature of the petiole
more proximally. The midrib then branches to a number of smaller
secondary veins, also known as second order veins, that extend toward
the leaf margins. These often terminate in a hydathode, a secretory
organ, at the margin. In turn, smaller veins branch from the secondary
veins, known as tertiary or third order (or higher order) veins,
forming a dense reticulate pattern. The areas or islands of mesophyll
lying between the higher order veins, are called areoles. Some of the
smallest veins (veinlets) may have their endings in the areoles, a
process known as areolation. These minor veins act as the sites of
exchange between the mesophyll and the plant's vascular system.
Thus minor veins collect the products of photosynthesis
(photosynthate) from the cells where it takes place, while major veins
are responsible for its transport outside of the leaf. At the same
time water is being transported in the opposite direction.
The number of vein endings is very variable, as is whether second
order veins end at the margin, or link back to other veins. There
are many elaborate variations on the patterns that the leaf veins
form, and these have functional implications. Of these, angiosperms
have the greatest diversity. Within these the major veins function
as the support and distribution network for leaves and are correlated
with leaf shape. For instance the parallel venation found in most
monocots correlates with their elongated leaf shape and wide leaf
base, while reticulate venation is seen in simple entire leaves, while
digitate leaves typically have venation in which three or more primary
veins diverge radially from a single point.
In evolutionary terms, early emerging taxa tend to have dichotomous
branching with reticulate systems emerging later. Veins appeared in
Homoblasty Characteristic in which a plant has small changes in leaf size, shape, and growth habit between juvenile and adult stages, in contrast to;
Heteroblasty Characteristic in which a plant has marked changes in leaf size, shape, and growth habit between juvenile and adult stages.
Anatomy (medium and small scale) Medium-scale features Leaves are normally extensively vascularised and typically have networks of vascular bundles containing xylem, which supplies water for photosynthesis, and phloem, which transports the sugars produced by photosynthesis. Many leaves are covered in trichomes (small hairs) which have diverse structures and functions.
Small-scale features The major tissue systems present are
The epidermis, which covers the upper and lower surfaces The mesophyll tissue inside the leaf, which is rich in chloroplasts (also called chlorenchyma) The arrangement of veins (the vascular tissue)
These three tissue systems typically form a regular organisation at the cellular scale. Specialised cells that differ markedly from surrounding cells, and which often synthesise specialised products such as crystals, are termed idioblasts.
Major leaf tissues
Cross-section of a leaf
Spongy mesophyll cells
SEM image of the leaf epidermis of Nicotiana alata, showing trichomes (hair-like appendages) and stomata (eye-shaped slits, visible at full resolution).
The epidermis is the outer layer of cells covering the leaf. It is
covered with a waxy cuticle which is impermeable to liquid water and
water vapor and forms the boundary separating the plant's inner cells
from the external world. The cuticle is in some cases thinner on the
lower epidermis than on the upper epidermis, and is generally thicker
on leaves from dry climates as compared with those from wet
climates. The epidermis serves several functions:
protection against water loss by way of transpiration, regulation of
gas exchange and secretion of metabolic compounds. Most leaves show
dorsoventral anatomy: The upper (adaxial) and lower (abaxial) surfaces
have somewhat different construction and may serve different
The epidermis tissue includes several differentiated cell types;
epidermal cells, epidermal hair cells (trichomes), cells in the
stomatal complex; guard cells and subsidiary cells. The epidermal
cells are the most numerous, largest, and least specialized and form
the majority of the epidermis. They are typically more elongated in
the leaves of monocots than in those of dicots.
An upper palisade layer of vertically elongated cells, one to two cells thick, directly beneath the adaxial epidermis, with intercellular air spaces between them. Its cells contain many more chloroplasts than the spongy layer. These long cylindrical cells are regularly arranged in one to five rows. Cylindrical cells, with the chloroplasts close to the walls of the cell, can take optimal advantage of light. The slight separation of the cells provides maximum absorption of carbon dioxide. Sun leaves have a multi-layered palisade layer, while shade leaves or older leaves closer to the soil are single-layered. Beneath the palisade layer is the spongy layer. The cells of the spongy layer are more branched and not so tightly packed, so that there are large intercellular air spaces between them for oxygen and carbon dioxide to diffuse in and out of during respiration and photosynthesis. These cells contain fewer chloroplasts than those of the palisade layer. The pores or stomata of the epidermis open into substomatal chambers, which are connected to the intercellular air spaces between the spongy and palisade mesophyll cells.
Leaves are normally green, due to chlorophyll in chloroplasts in the mesophyll cells. Plants that lack chlorophyll cannot photosynthesize. Vascular tissue
The veins of a bramble leaf
The veins are the vascular tissue of the leaf and are located in the spongy layer of the mesophyll. The pattern of the veins is called venation. In angiosperms the venation is typically parallel in monocotyledons and forms an interconnecting network in broad-leaved plants. They were once thought to be typical examples of pattern formation through ramification, but they may instead exemplify a pattern formed in a stress tensor field. A vein is made up of a vascular bundle. At the core of each bundle are clusters of two distinct types of conducting cells:
The xylem typically lies on the adaxial side of the vascular bundle
and the phloem typically lies on the abaxial side. Both are embedded
in a dense parenchyma tissue, called the sheath, which usually
includes some structural collenchyma tissue.
Some insects, like Kallima inachus, mimic leaves
Although not as nutritious as other organs such as fruit, leaves provide a food source for many organisms. The leaf is a vital source of energy production for the plant, and plants have evolved protection against animals that consume leaves, such as tannins, chemicals which hinder the digestion of proteins and have an unpleasant taste. Animals that are specialized to eat leaves are known as folivores. Some species have cryptic adaptations by which they use leaves in avoiding predators. For example, the caterpillars of some leaf-roller moths will create a small home in the leaf by folding it over themselves. Some sawflies similarly roll the leaves of their food plants into tubes. Females of the Attelabidae, so-called leaf-rolling weevils, lay their eggs into leaves that they then roll up as means of protection. Other herbivores and their predators mimic the appearance of the leaf. Reptiles such as some chameleons, and insects such as some katydids, also mimic the oscillating movements of leaves in the wind, moving from side to side or back and forth while evading a possible threat. Seasonal leaf loss
Leaves shifting color in autumn (fall)
Leaves in temperate, boreal, and seasonally dry zones may be
seasonally deciduous (falling off or dying for the inclement season).
This mechanism to shed leaves is called abscission. When the leaf is
shed, it leaves a leaf scar on the twig. In cold autumns, they
sometimes change color, and turn yellow, bright-orange, or red, as
various accessory pigments (carotenoids and xanthophylls) are revealed
when the tree responds to cold and reduced sunlight by curtailing
In the course of evolution, leaves have adapted to different environments in the following ways:
Waxy micro- and nanostructures on the surface reduce wetting by rain
and adhesion of contamination (See Lotus effect).
Divided and compound leaves reduce wind resistance and promote
Hairs on the leaf surface trap humidity in dry climates and create a
boundary layer reducing water loss.
Waxy plant cuticles reduce water loss.
Large surface area provides a large area for capture of sunlight.
In harmful levels of sunlight, specialised leaves, opaque or partly
buried, admit light through a translucent leaf window for
photosynthesis at inner leaf surfaces (e.g. Fenestraria).
Terminology See also: Glossary of leaf morphology, Glossary of plant morphology, and Glossary of botanical terms
Shape Main article: Glossary of leaf shapes
Leaves showing various morphologies. Clockwise from upper left: tripartite lobation, elliptic with serrulate margin, palmate venation, acuminate odd-pinnate (center), pinnatisect, lobed, elliptic with entire margin
Image Term Latin Description
Entire Forma integra Even; with a smooth margin; without toothing
Ciliate Ciliata Fringed with hairs
Crenate Crenata Wavy-toothed; dentate with rounded teeth
Dentate Dentata Toothed May be coarsely dentate, having large teeth or glandular dentate, having teeth which bear glands
Denticulate Denticulata Finely toothed
Doubly serrate Duplicato-dentata Each tooth bearing smaller teeth
Serrate Serrata Saw-toothed; with asymmetrical teeth pointing forward
Serrulate Serrulata Finely serrate
Sinuate Sinuosa With deep, wave-like indentations; coarsely crenate
Lobate Lobata Indented, with the indentations not reaching the center
Undulate Undulata With a wavy edge, shallower than sinuate
Spiny or pungent Spiculata With stiff, sharp points such as thistles
Image Term Latin Description
Acuminate _ Long-pointed, prolonged into a narrow, tapering point in a concave manner
Acute _ Ending in a sharp, but not prolonged point
Cuspidate _ With a sharp, elongated, rigid tip; tipped with a cusp
Emarginate _ Indented, with a shallow notch at the tip
Mucronate _ Abruptly tipped with a small short point
Mucronulate _ Mucronate, but with a noticeably diminutive spine
Obcordate _ Inversely heart-shaped
Obtuse _ Rounded or blunt
Truncate _ Ending abruptly with a flat end
Acuminate Coming to a sharp, narrow, prolonged point. Acute Coming to a sharp, but not prolonged point. Auriculate Ear-shaped. Cordate Heart-shaped with the notch towards the stalk. Cuneate Wedge-shaped. Hastate Shaped like an halberd and with the basal lobes pointing outward. Oblique Slanting. Reniform Kidney-shaped but rounder and broader than long. Rounded Curving shape. Sagittate Shaped like an arrowhead and with the acute basal lobes pointing downward. Truncate Ending abruptly with a flat end, that looks cut off.
Scale-shaped leaves of a Norfolk Island Pine, Araucaria heterophylla.
Coriaceous Leathery; stiff and tough, but somewhat flexible. Farinose Bearing farina; mealy, covered with a waxy, whitish powder. Glabrous Smooth, not hairy. Glaucous With a whitish bloom; covered with a very fine, bluish-white powder. Glutinous Sticky, viscid. Lepidote Coated with small scales (thus elepidote, without such scales). Maculate Stained, spotted, compare immaculate. Papillate, or papillose Bearing papillae (minute, nipple-shaped protuberances). Pubescent Covered with erect hairs (especially soft and short ones). Punctate Marked with dots; dotted with depressions or with translucent glands or colored dots. Rugose Deeply wrinkled; with veins clearly visible. Scurfy Covered with tiny, broad scalelike particles. Tuberculate Covered with tubercles; covered with warty prominences. Verrucose Warted, with warty outgrowths. Viscid, or viscous Covered with thick, sticky secretions.
The leaf surface is also host to a large variety of microorganisms; in this context it is referred to as the phyllosphere. Hairiness
Common mullein (Verbascum thapsus) leaves are covered in dense, stellate trichomes.
Scanning electron microscope
"Hairs" on plants are properly called trichomes. Leaves can show several degrees of hairiness. The meaning of several of the following terms can overlap.
Arachnoid, or arachnose With many fine, entangled hairs giving a cobwebby appearance. Barbellate With finely barbed hairs (barbellae). Bearded With long, stiff hairs. Bristly With stiff hair-like prickles. Canescent Hoary with dense grayish-white pubescence. Ciliate Marginally fringed with short hairs (cilia). Ciliolate Minutely ciliate. Floccose With flocks of soft, woolly hairs, which tend to rub off. Glabrescent Losing hairs with age. Glabrous No hairs of any kind present. Glandular With a gland at the tip of the hair. Hirsute With rather rough or stiff hairs. Hispid With rigid, bristly hairs. Hispidulous Minutely hispid. Hoary With a fine, close grayish-white pubescence. Lanate, or lanose With woolly hairs. Pilose With soft, clearly separated hairs. Puberulent, or puberulous With fine, minute hairs. Pubescent With soft, short and erect hairs. Scabrous, or scabrid Rough to the touch. Sericeous Silky appearance through fine, straight and appressed (lying close and flat) hairs. Silky With adpressed, soft and straight pubescence. Stellate, or stelliform With star-shaped hairs. Strigose With appressed, sharp, straight and stiff hairs. Tomentose Densely pubescent with matted, soft white woolly hairs.
Cano-tomentose Between canescent and tomentose. Felted-tomentose Woolly and matted with curly hairs.
Tomentulose Minutely or only slightly tomentose. Villous With long and soft hairs, usually curved. Woolly With long, soft and tortuous or matted hairs.
Hysteranthous Developing after the flowers  Synanthous Developing at the same time as the flowers 
Hickey primary venation types
2. Parallel venation, Iris
3. Campylodromous venation,
4. Acrodrous venation (basal),
5. Actinodromous venation (suprabasal),
6. Palinactodromous venation,
A number of different classification systems of the patterns of leaf veins (venation or veination) have been described, starting with Ettingshausen (1861), together with many different descriptive terms, and the terminology has been described as "formidable". One of the commonest among these is the Hickey system, originally developed for "dicotyledons" and using a number of Ettingshausen's terms derived from Greek (1973–1979): (see also: Simpson Figure 9.12, p. 468) Hickey system
There are three subtypes of pinnate venation:
Craspedodromous (Greek: kraspedon - edge, dromos - running) The major veins reach to the margin of the leaf. Camptodromous Major veins extend close to the margin, but bend before they intersect with the margin. Hyphodromous All secondary veins are absent, rudimentary or concealed
These in turn have a number of further subtypes such as eucamptodromous, where secondary veins curve near the margin without joining adjacent secondary veins.
2. Parallelodromous (parallel-veined, parallel-ribbed, parallel-nerved, penniparallel, striate) Two or more primary veins originating beside each other at the leaf base, and running parallel to each other to the apex and then converging there. Commissural veins (small veins) connect the major parallel veins. Typical for most monocotyledons, such as grasses.
The additional terms marginal (primary veins reach the margin), and reticulate (primary veins do not reach the margin) are also used.
3. Campylodromous (campylos - curve)
Several primary veins or branches originating at or close to a single
point and running in recurved arches, then converging at apex. E.g.
Two or more primary or well developed secondary veins in convergent
arches towards apex, without basal recurvature as in Campylodromous.
May be basal or suprabasal depending on origin, and perfect or
imperfect depending on whether they reach to 2/3 of the way to the
Three or more primary veins diverging radially from a single point.
E.g., Arcangelisia (basal type),
6. Palinactodromous Primary veins with one or more points of secondary dichotomous branching beyond the primary divergence, either closely or more distantly spaced. E.g., Platanus.
Types 4–6 may similarly be subclassified as basal (primaries joined
at the base of the blade) or suprabasal (diverging above the blade
base), and perfect or imperfect, but also flabellate.
At about the same time, Melville (1976) described a system applicable
Branching repeatedly by regular dichotomy to give rise to a three
dimensional bush-like structure consisting of linear segment (2
Primary veins straight or only slightly curved, diverging from the
base in a fan-like manner (4 subclasses)
Curved primary veins (3 subclasses)
A modified form of the Hickey system was later incorporated into the Smithsonian classification (1999) which proposed seven main types of venation, based on the architecture of the primary veins, adding Flabellate as an additional main type. Further classification was then made on the basis of secondary veins, with 12 further types, such as;
Brochidodromous Closed form in which the secondaries are joined together in a series of prominent arches, as in Hildegardia. Craspedodromous Open form with secondaries terminating at the margin, in toothed leaves, as in Celtis. Eucamptodromous Intermediate form with upturned secondaries that gradually diminish apically but inside the margin, and connected by intermediate tertiary veins rather than loops between secondaries, as in Cornus. Cladodromous Secondaries freely branching toward the margin, as in Rhus.
terms which had been used as subtypes in the original Hickey system.
Secondary venation patterns
Brochidodromous Hildegardia migeodii
Further descriptions included the higher order, or minor veins and the
patterns of areoles (see
Flabellate venation, Adiantum cunninghamii
Flabellate Several to many equal fine basal veins diverging radially at low angles and branching apically. E.g. Paranomus.
Analyses of vein patterns often fall into consideration of the vein orders, primary vein type, secondary vein type (major veins), and minor vein density. A number of authors have adopted simplified versions of these schemes. At its simplest the primary vein types can be considered in three or four groups depending on the plant divisions being considered;
pinnate palmate parallel
where palmate refers to multiple primary veins that radiate from the
petiole, as opposed to branching from the central main vein in the
pinnate form, and encompasses both of Hickey types 4 and 5, which are
preserved as subtypes; e.g., palmate-acrodromous (see National Park
Palmate venation, Acer truncatum
Palmate, Palmate-netted, palmate-veined, fan-veined Several main veins of approximately equal size diverge from a common point near the leaf base where the petiole attaches, and radiate toward the edge of the leaf. Palmately veined leaves are often lobed or divided with lobes radiating from the common point. They may vary in the number of primary veins (3 or more), but always radiate from a common point. e.g. most Acer (maples).
Other systems Alternatively, Simpson uses:
Central midrib with no lateral veins (microphyllous), seen in the
non-seed bearing tracheophytes, such as horsetails
Veins successively branching into equally sized veins from a common
point, forming a Y junction, fanning out. Amongst temperate woody
Equisetum: Reduced microphyllous leaves (L) arising in whorl from node
However, these simplified systems allow for further division into multiple subtypes. Simpson, (and others) divides parallel and netted (and some use only these two terms for Angiosperms) on the basis of the number of primary veins (costa) as follows;
Penni-parallel (pinnate, pinnate parallel, unicostate parallel) Single central prominent midrib, secondary veins from this arise perpendicularly to it and run parallel to each other towards the margin or tip, but do not join (anastomose). The term unicostate refers to the prominence of the single midrib (costa) running the length of the leaf from base to apex. e.g. Zingiberales, such as Bananas etc. Palmate-parallel (multicostate parallel) Several equally prominent primary veins arising from a single point at the base and running parallel towards tip or margin. The term multicostate refers to having more than one prominent main vein. e.g. "fan" (palmate) palms (Arecaceae)
Multicostate parallel convergent
Mid-veins converge at apex e.g.
Multicostate convergent Major veins diverge from origin at base then converge towards the tip. e.g. Zizyphus, Smilax, Cinnamomum Multicostate divergent All major veins diverge towards the tip. e.g. Gossypium, Cucurbita, Carica papaya, Ricinus communis
Three primary veins, as above, e.g. (see)
Simpson venation patterns
Bambusa bambos: Multicostate parallel convergent
Liquidambar styraciflua: Palmately netted
Ziziphus jujuba: Multicostate palmate convergent
These complex systems are not used much in morphological descriptions of taxa, but have usefulness in plant identification,  although criticized as being unduly burdened with jargon. An older, even simpler system, used in some flora uses only two categories, open and closed.
Open: Higher order veins have free endings among the cells and are more characteristic of non-monocotyledon angiosperms. They are more likely to be associated with leaf shapes that are toothed, lobed or compound. They may be subdivided as;
Closed: Higher order veins are connected in loops without ending freely among the cells. These tend to be in leaves with smooth outlines, and are characteristic of monocotyledons.
They may be subdivided into whether the veins run parallel, as in grasses, or have other patterns.
Other descriptive terms There are also many other descriptive terms, often with very specialised usage and confined to specific taxonomic groups. The conspicuousness of veins depends on a number of features. These include the width of the veins, their prominence in relation to the lamina surface and the degree of opacity of the surface, which may hide finer veins. In this regard, veins are called obscure and the order of veins that are obscured and whether upper, lower or both surfaces, further specified. Terms that describe vein prominence include bullate, channelled, flat, guttered, impressed, prominent and recessed (Fig. 6.1 Hawthorne & Lawrence 2013). Veins may show different types of prominence in different areas of the leaf. For instance Pimenta racemosa has a channelled midrib on the upper surfae, but this is prominent on the lower surface. Describing vein prominence:
Surface of leaf raised in a series of domes between the veins on the
upper surface, and therefore also with marked depressions. e.g.
Rytigynia pauciflora, Vitis vinifera
Veins sunken below the surface, resulting in a rounded channel.
Sometimes confused with "guttered" because the channels may function
as gutters for rain to run off and allow drying, as in many
Melastomataceae. e.g. (see)
Types of vein prominence
Vitis vinifera Bullate
Clidemia hirta Channeled
Berberis gagnepainii Obscure (under surface)
Viburnum plicatum Recessed
Describing other features:
More than one main vein (nerve) at the base. Lateral secondary veins
branching from a point above the base of the leaf. Usually expressed
as a suffix, as in 3-plinerved or triplinerved leaf. In a 3-plinerved
(triplinerved) leaf three main veins branch above the base of the
lamina (two secondary veins and the main vein) and run essentially
parallel subsequently, as in
Diagrams of venation patterns
Image Term Description
Arcuate Secondary arching toward the apex
Dichotomous Veins splitting in two
Longitudinal All veins aligned mostly with the midvein
Parallel All veins parallel and not intersecting
Pinnate Secondary veins borne from midrib
Reticulate All veins branching repeatedly, net veined
Rotate Veins coming from the center of the leaf and radiating toward the edges
Transverse Tertiary veins running perpendicular to axis of main vein, connecting secondary veins
Glossary of leaf morphology
Glossary of plant morphology:Leaves
Evolutionary history of leaves
Evolutionary development of leaves
^ a b Esau 2006.
^ Cutter 1969.
^ Haupt 1953.
^ a b Mauseth 2009.
^ James et al 1999.
^ a b c d e Stewart & Rothwell 1993.
^ Cooney-Sovetts & Sattler 1987.
^ Tsukaya 2013.
^ Feugier 2006.
^ Purcell 2016.
^ Willert et al 1992.
^ Bayer 1982.
^ Marloth 1913–1932.
^ a b Simpson 2011, p. 356.
^ Krogh 2010.
^ James & Bell 2000.
^ Heywood et al 2007.
^ Hallé 1977.
^ Rolland-Lagan et al 2009.
^ a b c Walls 2011.
^ a b c Dickison 2000.
^ a b Rudall 2007.
^ a b c d e f g h i Simpson 2011,
Books and chapters
Arber, Agnes (1950). The Natural Philosophy of
Prance, Ghillean Tolmie (1985). Leaves: the formation, characteristics
and uses of hundreds of leaves found in all parts of the world.
Photographs by Kjell B. Sandved. London: Thames and Hudson.
Rines, George Edwin, ed. (1920). The Encyclopedia Americana. NY:
Americana. (see The Encyclopedia Americana)
Rudall, Paula J. (2007). Anatomy of flowering plants: an introduction
to structure and development (3rd ed.). Cambridge: Cambridge
University Press. ISBN 9780521692458.
Simpson, Michael G. (2011).
Articles and theses
Cooney-Sovetts, C.; Sattler, R. (1987). "
Bucksch, Alex; Blonder, Benjamin; Price, Charles; Wing, Scott; Weitz,
Joshua; Das, Abhiram (2017). "Cleared
Kling, Gary J.; Hayden, Laura L.; Potts, Joshua J. (2005). "Botanical
terminology". University of Illinois, Urbana-Champaign. Retrieved 7
de Kok, Rogier; Biffin, Ed (November 2007). "The
"Leaves". , in Massey & Murphy (1996)
Purcell, Adam (16 January 2016). "Leaves". Basic Biology. Adam
Purcell. Retrieved 17 February 2017.
Simpson, Michael G. "Plants of San Diego County, California". College
of Science, San Diego State University. Retrieved 2 March 2017.
"Florissant Fossil Beds
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