Leaf

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Leaf

In botany

Botany

Botany, plant science, phytology, or plant biology is a branch of biology and is the Scientific method of plant life and development....
, a leaf is an above-ground plant

Plant

Plants are Life organisms belonging to the Kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae....
organ

Organ (anatomy)

In biology, an organ is a biological tissue that performs a specific function or group of functions. Usually there is a main tissue and sporadic tissues....
specialized for photosynthesis

Photosynthesis

File:Seawifs global biosphere.jpgPhotosynthesis is a metabolic pathway that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight....
. For this purpose, a leaf is typically flat (laminar) and thin, to expose the cells containing chloroplast

Chloroplast

Chloroplasts are organelles found in plant cells and other eukaryote organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve Thermodynamic free energy in the form of Adenosine triphosphate and reduce NADP to NADPH through a complex set of processes called photosynthesis....
to light

Light

Light, or visible light, is electromagnetic radiation of a wavelength that is Visible spectrum to the human eye , or up to 380?750 nm. In the broader field of physics, light is sometimes used to refer to electromagnetic radiation of all wavelengths, whether visible or not....
over a broad area, and to allow light to penetrate fully into the tissues.

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Leaf anatomy

A structurally complete leaf of an angiosperm

Flowering plant

The flowering plants or angiosperms are the most widespread group of Embryophytes. The flowering plants and the gymnosperms are the only extant groups of Spermatophyte....
consists of a petiole

Petiole (botany)

In botany, the petiole is the small stalk attaching the leaf blade to the Plant stem. The petiole usually has the same internal structure as the stem....
(leaf stem), a lamina (leaf blade), and stipule

Stipule

In botany, stipule is a term coined by Carolus Linnaeus which refers to outgrowths borne on either side of the base of a leafstalk . A pair of stipules is considered part of the anatomy of the leaf of a typical flowering plant, although in many species the stipules are inconspicuous or entirely absent ....
s (small processes located to either side of the base of the petiole). The petiole attaches to the stem at a point called the "leaf axil". Not every species produces leaves with all of the aforementioned structural components. In some species, paired stipules are not obvious or are absent altogether. A petiole may be absent, or the blade may not be laminar (flattened). The tremendous variety shown in leaf structure (anatomy) from species to species is presented in detail below under Leaf morphology. After a period of time (i.e. seasonally, during the autumn), deciduous trees shed their leaves. These leaves then decompose into the soil.

A leaf is considered a plant organ and typically consists of the following tissues:

An epidermis that covers the upper and lower surfaces
An interior chlorenchyma called the mesophyll
An arrangement of veins (the vascular tissue).

Epidermis

The epidermis

Epidermis (botany)

The epidermis is a single-layered group of cells that covers plants leaf, flowers, roots and Plant stem. It forms a boundary between the plant and the external world....
is the outer multi-layered group of cells

Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
covering the leaf. It forms the boundary separating the plant's inner cells from the external world. The epidermis serves several functions: protection against water loss, regulation of gas exchange, secretion of metabolic

Metabolism

Metabolism is the set of chemical reactions that occur in living organisms in order to maintain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments....
compounds, and (in some species) absorption of water. Most leaves show dorsoventral anatomy: the upper (adaxial) and lower (abaxial) surfaces have somewhat different construction and may serve different functions.

The epidermis is usually transparent

Transparency (optics)

In optics, transparency is the material property of allowing light to pass through. In mineralogy, another term for this property is diaphaneity....
(epidermal cells lack chloroplasts) and coated on the outer side with a waxy cuticle

Plant cuticle

Plant cuticles are a protective waxy covering produced only by the Epidermis of leaf, young shoots and all other aerial plant organs without periderm....
that prevents water loss. The cuticle is in some cases thinner on the lower epidermis than on the upper epidermis, and is thicker on leaves from dry climates as compared with those from wet climates.

The epidermis tissue includes several differentiated cell types: epidermal cells, guard cells, subsidiary cells, and epidermal hairs (trichome

Trichome

Trichomes, from the Greek language meaning "growth of hair", are fine outgrowths or appendages on plants and certain protists. These are of diverse structure and function....
s). The epidermal cells are the most numerous, largest, and least specialized. These are typically more elongated in the leaves of monocots than in those of dicots.

The epidermis is covered with pores called stoma
Stoma

In botany, a stoma is a pore, found in the leaf and stem epidermis that is used forgas exchange. The pore is formed by a pair of specialized parenchyma cells known as guard cells which are responsible for regulating the size of the opening....
ta, part of a stoma complex consisting of a pore surrounded on each side by chloroplast-containing guard cells, and two to four subsidiary cells that lack chloroplasts. The stoma complex regulates the exchange of gases and water vapor between the outside air and the interior of the leaf. Typically, the stomata are more numerous over the abaxial (lower) epidermis than the adaxial (upper) epidermis.

Mesophyll

Most of the interior of the leaf between the upper and lower layers of epidermis is a parenchyma
Parenchyma

Parenchyma is a term used to describe a bulk of a substance. It is used in different ways in animals and in plants.The term is New Latin, from Greek language parenkhuma, visceral flesh, from parenkhein, to pour in beside : para-, beside + en-, in + khein, to pour....
(ground tissue) or chlorenchyma tissue called the mesophyll (Greek for "middle leaf"). This assimilation

Assimilation (biology)

Biological assimilation, or bioassimilation, involves one of two different processes to supply animal cells with nutrients. The first is the process of absorbing vitamins, minerals, and other chemicals from food within the gastrointestinal tract....
tissue is the primary location of photosynthesis in the plant. The products of photosynthesis are called "assimilates". In ferns and most flowering plants the mesophyll is divided into two layers:

An upper palisade layer
Palisade cell

Palisade cells are a type of leaf Tissue and can be found within the mesophyll in leaves of dicotyledonous plants. They contain chloroplasts, which convert the energy stored in photons to chemical energy through photosynthesis....
of tightly packed, vertically elongated cells, one to two cells thick, directly beneath the adaxial epidermis. 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
Absorption (chemistry)

File:Absorber.svgAbsorption, in chemistry, is a physical or chemical phenomenon or a Process in which atoms, molecules, or ions enter some bulk phase - gas, liquid or solid material....
of carbon dioxide. This separation must be minimal to afford capillary action
Capillary action

Capillary action, capillarity, capillary motion, or wicking refers to two phenomena:# The movement of liquids in thin tubes...
for water distribution. In order to adapt to their different environment (such as sun or shade), plants had to adapt this structure to obtain optimal result. 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 rounded and not so tightly packed. There are large intercellular air spaces. These cells contain fewer chloroplasts than those of the palisade layer.

The pores or stomata of the epidermis open into substomatal chambers, connecting to air spaces between the spongy layer cells.

These two different layers of the mesophyll are absent in many aquatic and marsh plants. Even an epidermis and a mesophyll may be lacking. Instead for their gaseous exchanges they use a homogeneous aerenchyma
Aerenchyma

Aerenchyma is an airy tissue found in roots of plants, which allows exchange of gases between the shoot and the root. It contains large air-filled cavities, which provide a low-resistance internal pathway for the exchange of gases such as oxygen and ethylene between the plant parts above the water and the submerged tissues....
(thin-walled cells separated by large gas-filled spaces). Their stomata are situated at the upper surface.

Leaves are normally green

Green

Green is a color, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 520?570-Nanometre....
in color, which comes from chlorophyll

Chlorophyll

Chlorophyll is a green pigment found in most plants, algae, and cyanobacteria. Its name is derived from Greek language: ?????? and f????? ....
found in plastid

Plastid

Plastids are major organelles found in plants and algae. Plastids are the site of manufacture and storage of important chemical compounds used by the cell....
s in the chlorenchyma cells. Plants that lack chlorophyll cannot photosynthesize

Photosynthesis

Temperate

In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally mild, rather than extreme hot or cold....
, boreal

Boreal

Boreal may refer to*Northern, from Boreas, god of the North Wind in Greek mythology*Boreal climate, the climate found in a region of boreal forests, and designated Dfc, Dwc or Dsc in the K?ppen climate classification scheme....
, and seasonally dry zones may be seasonally deciduous

Deciduous

Deciduous means falling off at maturity or tending to fall off and is typically used in reference to trees or shrubs that lose their leaves seasonally and to the shedding of other plant structures such as petals after flowering or fruit when ripe....
(falling off or dying for the inclement season). This mechanism to shed leaves is called abscission

Abscission

Abscission is the shedding of a body part. It most commonly refers to the process by which a plant intentionally drops one or more of its parts, such as a leaf, fruit, flower or seed, though the term is also used to describe the shedding of a claw by an animal, and is also the word used to describe the separation of daughter cells at the end...
. After the leaf is shed, a leaf scar develops on the twig. In cold autumns they sometimes change color

Autumn leaf color

Autumn leaf color is a phenomenon that affects the normally green leaves of many deciduous trees and shrubs by which they take on, during a few weeks in the autumn season, one or many colors that range from red to yellow....
, and turn yellow

Yellow

Yellow is the color evoked by light that stimulates both the L and M cone cells of the retina about equally, but does not significantly stimulate the S cone cells; that is, light with much red and green but not very much blue....
, bright orange

Orange (colour)

The color orange occurs between red and yellow in the visible Optical spectrum at a wavelength of about 585 ? 620 nanometre, and has a hue of 30? in HSV colour space....
or red

Red

Red is any of a number of similar colors evoked by light consisting predominantly of the longest wavelengths of light discernible by the human eye, in the wavelength range of roughly 625?740 Nanometer....
as various accessory pigments (carotenoid

Carotenoid

Carotenoids are organic compound pigments that are naturally occurring in chromoplasts of plants and some other photosynthesis organisms like algae, some types of fungus and some bacterium....
s and xanthophyll

Xanthophyll

Xanthophylls are yellow pigments from the carotenoid group. Their molecular structure is based on carotenes; contrary to the carotenes, some hydrogen atoms are substituted by hydroxyl groups and/or some pairs of hydrogen atoms are substituted by oxygen atoms....
s) are revealed when the tree responds to cold and reduced sunlight

Sunlight

Sunlight, in the broad sense, is the total spectroscopy of the electromagnetic radiation given off by the Sun. On Earth, sunlight is Filter ed through the Earth's atmosphere, and the solar radiation is obvious as daylight when the Sun is above the horizon....
by curtailing chlorophyll production. Red anthocyanin pigments are now thought to be produced in the leaf as it dies, possibly to mask the yellow hue left when the chlorophyll is lost - yellow leaves appear to attract herbivores such as aphids.

Veins

The veins are the vascular tissue

Vascular tissue

Vascular tissue is a complex conducting tissue , formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and phloem....
of the leaf and are located in the spongy layer of the mesophyll. They are typical examples of pattern formation

Pattern formation

The science of pattern formation deals with the visible, Similarity outcomes of self-organisation and the common principles behind similar patterns....
through ramification

Ramification (botany)

In botany, ramification is the divergence of the Plant stem and limbs of a plant into smaller ones, i.e. trunk into branches, branches into increasingly smaller branches, etc....
. The pattern of the veins is called venation.

The veins are made up of:

xylem
Xylem

In vascular plants, xylem is one of the two types of transport tissue, phloem being the other. The word "xylem" is derived from classical Greek language ????? , "wood", and indeed the best known xylem tissue is wood, though it is found throughout the plant....
, tubes that brings water and minerals from the roots into the leaf.
phloem
Phloem

In vascular plants, phloem is the living Biological tissue that carries organic nutrients , particularly sucrose, a sugar, to all parts of the plant where needed....
, tubes that usually moves sap
Sap

Sap may refer to:* Plant sap, the fluid transported in xylem cells or phloem sieve tube elements of a plant* Baton #Blackjack, another word for a blackjack, an easily concealed Club ....
, with dissolved sucrose, produced by photosynthesis in the leaf, out of the leaf.

The xylem typically lies over the phloem. Both are embedded in a dense parenchyma tissue, called "pith", with usually some structural collenchyma tissue present.

Leaf morphology

leaf is identified by the pores and pigments, as well as the margins.]] External leaf characteristics (such as shape, margin, hairs, etc.) are important for identifying plant species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring....
, and botanists have developed a rich terminology

Terminology

Terminology is the study of terms and their use. Terms are words and compound words that are used in specific contexts. Not to be confused with "terms" in colloquial usages, the shortened form of technical terms which are defined within a Academic discipline or speciality field....
for describing leaf characteristics. These structures are a part of what makes leaves determinant; they grow and achieve a specific pattern and shape, then stop. Other plant parts like stems or roots are non-determinant, and will usually continue to grow as long as they have the resources to do so.

Classification of leaves can occur through many different designative schema, and the type of leaf is usually characteristic of a species, although some species produce more than one type of leaf. The longest type of leaf is a leaf from palm trees, measuring at nine feet long. The terminology associated with the description of leaf morphology is presented, in illustrated form, at .

Basic leaf types

* Fern

Fern

A fern is any one of a group of about 20,000 species of plants classified in the phylum or division Pteridophyta, also known as Filicophyta....
s have fronds.

Conifer leaves are typically needle-, awl-, or scale-shaped
Angiosperm
Flowering plant

The flowering plants or angiosperms are the most widespread group of Embryophytes. The flowering plants and the gymnosperms are the only extant groups of Spermatophyte....
(flowering plant) leaves: the standard form includes stipules, a petiole, and a lamina.
Lycophytes
Lycopodiophyta

The Division Lycopodiophyta is a vascular plant subdivision of the Kingdom Plantae. It is the oldest extant vascular plant division at around 420 million years old, and includes some of the most "primitive" extant species....
have microphyll
Microphyll

The terminology of fossil plants is in places a little confusing. In the discipline's 200+ year history, certain concepts have become entrenched, even though improved understanding has threatened the foundations upon which they are based....
leaves.
Sheath
Monocotyledon

Monocotyledons or monocots are one of two major groups of flowering plants that are traditionally recognised, the other being dicotyledons or dicots....
leaves (type found in most grasses
Poaceae

Poaceae or Gramineae is a family in the Class Liliopsida of the Magnoliophyta. Plants of this family are usually called grasses; the shrub- or tree-like plants in this family are called bamboo ....
).
Other specialized leaves (such as those of Nepenthes
Nepenthes

The Nepenthes , popularly known as Tropical pitcher plants or Monkey Cups, are a genus of carnivorous plants in the monotypic family Nepenthaceae that comprises roughly 120 species, numerous List of Nepenthes natural hybrids and many cultivated hybrids....
)

Arrangement on the stem

Different terms are usually used to describe leaf placement (phyllotaxis

Phyllotaxis

In botany, phyllotaxis or phyllotaxy is the arrangement of the leaf on the plant stem of a plant....
):

* Alternate — leaf attachments are singular at nodes, and leaves alternate direction, to a greater or lesser degree, along the stem.

Opposite — leaf attachments are paired at each node; decussate if, as typical, each successive pair is rotated 90° progressing along the stem; or distichous if not rotated, but two-ranked (in the same geometric flat-plane).
Whorled — three or more leaves attach at each point or node on the stem. As with opposite leaves, successive whorls may or may not be decussate, rotated by half the angle between the leaves in the whorl (i.e., successive whorls of three rotated 60°, whorls of four rotated 45°, etc). Opposite leaves may appear whorled near the tip of the stem.
Rosulate — leaves form a rosette
Rosette (botany)

In botany, a rosette is a circular arrangement of leaves, with all the leaves at a single height.Though rosettes usually sit near the soil, their structure is an example of a modified stem....

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

Helix

A helix is a special kind of space curve, i.e. a Differentiable manifold curve in three-space. As a mental image of a helix one may take the spring ....
pattern centred 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 a limit of 360° x 34/89 = 137.52 or 137° 30', an angle known mathematically as the golden angle

Golden angle

In geometry, the golden angle is the smaller of the two angles created by sectioning the circumference of a circle according to the golden section; that is, into two Arc s such that the ratio of the length of the larger arc to the smaller is the same as the ratio of the full circumference to the larger....
. In the series, the numerator

Numerator

Numerator may refer to:* A numeral used to indicate a count, particularly of the equal parts in a fraction . A numerator is the number on top of the fraction....
indicates the number of complete turns or "gyres" until a leaf arrives at the initial position. 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) : three leaves in one circle
144° (or 2/5) : five leaves in two gyres
135° (or 3/8) : eight leaves in three gyres.

Divisions of the lamina (blade)

Two basic forms of leaves can be described considering the way the blade is divided. A simple leaf has an undivided blade. However, the leaf shape may be formed of lobes, but the gaps between lobes do not reach to the main vein. A compound leaf has a fully subdivided blade, each leaflet

Leaflet

A leaflet in botany is a part of a compound leaf. A leaflet may resemble an entire leaf leaf, but it is not borne on a Plant stem as a leaf is, but rather on a vein of the whole leaf ....
of the blade separated along a main or secondary vein. 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

Fabaceae

Fabaceae or Leguminosae is a large and economically important family of flowering plants, which is commonly known as the legume family, pea family, bean family or pulse family....
. The middle vein of a compound leaf or a frond

Frond

Rachis

The rachis is the main axis of the inflorescence, or spike, of wheat and other cereals, to which the spikelets are attached. It is also the part of the axis that the pinnae are attached to in ferns, the main stem of a compound leaf , or the main axis in compound inflorescences in other angiosperms....
.

Palmately compound leaves have the leaflets radiating from the end of the petiole, like fingers off the palm of a hand, e.g. Cannabis
Cannabis

Cannabis is a genus of flowering plants that includes three putative species, Cannabis sativa L., Cannabis indica Lam., and Cannabis ruderalis Janisch....
(hemp) and Aesculus
Aesculus

The genus Aesculus, the buckeyes and Horse Chestnuts, comprises 13-19 species of woody trees and shrubs native to the temperate northern hemisphere, with 6 species native to North America and 7-13 species native to Eurasia; there are also several Hybrid ....
(buckeyes).
Pinnately compound leaves have the leaflets arranged along the main or mid-vein.

odd pinnate: with a terminal leaflet, e.g. Fraxinus
Ash tree

Fraxinus is a genus of usually medium to large trees, mostly deciduous though a few subtropical species are evergreen. The leaf are opposite , and mostly pinnately-compound, simple in a few species....
(ash).
even pinnate: lacking a terminal leaflet, e.g. Swietenia
Mahogany

The name mahogany is used when referring to numerous varieties of dark-colored wood, originally the wood of the species Swietenia mahagoni, known as West Indian or Cuban mahogany....
(mahogany).

Bipinnately compound 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 pinnules on one secondary vein are called "pinna"; e.g. Albizia
Albizia

Albizia is a genus of about 150 species of mostly fast-growing subtropical and tropical trees and shrubs in the Subfamily Mimosoideae of the legume family, Fabaceae....
(silk tree).
trifoliate: a pinnate leaf with just three leaflets, e.g. Trifolium
Clover

Clover , or trefoil, is a genus of about 300 species of plants in the pea family Fabaceae. The genus has a cosmopolitan distribution; the highest diversity is found in the temperate Northern Hemisphere, but many species also occur in South America and Africa, including at high altitudes on mountains in the tropics....
(clover), Laburnum
Laburnum

Laburnum is a genus of two species of small trees in the subfamily Faboideae of the pea family Fabaceae, Laburnum anagyroides and Laburnum alpinum ....
(laburnum).
pinnatifid: pinnately dissected to the midrib, but with the leaflets not entirely separate, e.g. Polypodium
Polypodium

Polypodium is a genus of between 75-100 species of true ferns, widely distributed throughout the world, with the highest species diversity in the tropics....
, some Sorbus
Sorbus

Sorbus is a genus of about 100?200 species of trees and shrubs in the subfamily Maloideae of the Rose family Rosaceae. Species of Sorbus are commonly known as whitebeam, rowan, service tree, and Sorbus aucuparia....
(whitebeams).

Characteristics of the petiole

Petiolated leaves have a petiole

Petiole (botany)

In botany, the petiole is the small stalk attaching the leaf blade to the Plant stem. The petiole usually has the same internal structure as the stem....
. Sessile leaves do not: the blade attaches directly to the stem. In clasping or decurrent leaves, the blade partially or wholly surrounds the stem, often giving the impression that the shoot grows through the leaf. When this is actually the case, the leaves are called "perfoliate", such as in Claytonia perfoliata
Claytonia perfoliata

Claytonia perfoliata is a fleshy annual plant native to the western mountain and coastal regions of North America from southernmost Alaska and central British Columbia south to Central America, but most common in California in the Sacramento Valley and northern San Joaquin Valley valleys....
. In peltate leaves, the petiole attaches to the blade inside from the blade margin.

In some Acacia
Acacia

Acacia is a genus of shrubs and trees belonging to the subfamily Mimosoideae of the family Fabaceae, first described in Africa by the Sweden botanist Carolus Linnaeus in 1773....
species, such as the Koa Tree (Acacia koa), the petioles are expanded or broadened and function like leaf blades; these are called phyllodes. There may or may not be normal pinnate leaves at the tip of the phyllode.

A stipule

Stipule

Dicotyledon

Dicotyledons, or "dicots", is a name for a group of flowering plants whose seed typically has two embryonic leaves or cotyledons. There are around 199,350 species within this group....
s, is an appendage on each side at the base of the petiole resembling a small leaf. Stipules may be lasting and not be shed (a stipulate leaf, such as in rose

Rose

A rose is a perennial plant flower shrub or vine of the genus Rosa, within the family Rosaceae, that contains over 100 species and comes in a variety of colors....
s and bean

Bean

Bean is a common name for large plant seeds of several genus of the Family Fabaceae used for human food or animal feed.The whole young pods of bean plants, if picked before the pods ripen and dry, can be tender enough to eat whole, whether cooked or raw....
s), or be shed as the leaf expands, leaving a stipule scar on the twig (an exstipulate leaf).

The situation, arrangement, and structure of the stipules is called the "stipulation".

free
adnate : fused to the petiole base
ochreate : provided with ochrea
Ochrea

Ochrea, commonly spelled ocrea, is a structure formed of stipules fused into a sheath surrounding the stem. It is a diagnostic character in the Polygonaceae....
, or sheath-formed stipules, e.g. rhubarb
Rhubarb

Rheum is a genus of perennial plants that grows from thick short rhizomes. The genus is in the family Polygonaceae, and includes the vegetable rhubarb The plants have large leaf that are somewhat triangular shaped with long fleshy Petiole s....
,
encircling the petiole base
interpetiolar : between the petioles of two opposite leaves.
intrapetiolar : between the petiole and the subtending stem

Venation (arrangement of the veins)

There are two subtypes of venation, namely, craspedodromous, where the major veins stretch up to the margin of the leaf, and camptodromous, when major veins extend close to the margin, but bend before they intersect with the margin.

Feather-veined, reticulate — the veins arise pinnately from a single mid-vein and subdivide into veinlets. These, in turn, form a complicated network. This type of venation is typical for (but by no means limited to) dicotyledon
Dicotyledon

Dicotyledons, or "dicots", is a name for a group of flowering plants whose seed typically has two embryonic leaves or cotyledons. There are around 199,350 species within this group....
s.

Pinnate-netted, penniribbed, penninerved, penniveined; the leaf has usually one main vein (called the mid-vein), with veinlets, smaller veins branching off laterally, usually somewhat parallel to each other; eg Malus
Malus

Malus, the apples, is a genus of about 30?35 species of small deciduous trees or shrubs in the family Rosaceae. Other studies go as far as 55 species including the domesticated Apple, or Table apple as it was formerly called ....
(apples).
Three main veins branch at the base of the lamina and run essentially parallel subsequently, as in Ceanothus
Ceanothus

Ceanothus Carolus Linnaeus is a genus of about 50?60 species of shrubs or small trees in the buckthorn family Rhamnaceae. The genus is confined to North America, the center of its distribution in California, with some species in the eastern United States and southeast Canada, and others extending as far south as Guatemala....
. A similar pattern (with 3-7 veins) is especially conspicuous in Melastomataceae
Melastomataceae

The family Melastomataceae is a taxon of dicots flowering plants found mostly in the tropics comprising some 200 genera and 4500 species. Melastomes are annual or perennial herbs, shrubs, or small trees....
.
Palmate-netted, palmate-veined, fan-veined; several main veins diverge
Divergence

In vector calculus, the divergence is an operator that measures the magnitude of a vector field's source or sink at a given point; the divergence of a vector field is a scalar....
from near the leaf base where the petiole attaches, and radiate toward the edge of the leaf; e.g. most Acer
Maple

Acer is a genus of trees or shrubs commonly known as Maple. Maples are variously classified in a family of their own, the Aceraceae, or included in the family Sapindaceae....
(maples).

Parallel-veined, parallel-ribbed, parallel-nerved, penniparallel — veins run parallel
Parallel (geometry)

Parallelism is a term in geometry and in everyday life that refers to a property in Euclidean space of two or more line s or plane , or a combination of these....
for the length of the leaf, from the base to the apex. Commissural veins (small veins) connect the major parallel veins. Typical for most monocotyledon
Monocotyledon

Monocotyledons or monocots are one of two major groups of flowering plants that are traditionally recognised, the other being dicotyledons or dicots....
s, such as grasses
Poaceae

Poaceae or Gramineae is a family in the Class Liliopsida of the Magnoliophyta. Plants of this family are usually called grasses; the shrub- or tree-like plants in this family are called bamboo ....
.
Dichotomous — There are no dominant bundles, with the veins forking regularly by pairs; found in Ginkgo
Ginkgo

Ginkgo , frequently misspelled as "Gingko", and also known as the Maidenhair Tree after Adiantum, is a unique species of tree with no close living relatives....
and some pteridophyte
Fern

A fern is any one of a group of about 20,000 species of plants classified in the phylum or division Pteridophyta, also known as Filicophyta....
s.

Note that although it is the more complex pattern, branching veins appear to be plesiomorphic and in some form were present in ancient seed plants as long as 250 million years ago. A pseudo-reticulate venation that is actually a highly modified penniparallel one is an autapomorphy of some Melanthiaceae

Melanthiaceae

Melanthiaceae is a family of flowering plants perennial plant herbs in the Northern Hemisphere. The family has been recognized by relatively few taxonomists, and the circumscription has varied....
which are monocots, e.g. Paris quadrifolia
Paris quadrifolia

Paris quadrifolia is a species of the genus Paris in the family Melanthiaceae although authorities formerly regarded it as part of the Liliaceae family....
(True-lover's Knot).

Leaf morphology changes within a single plant

Homoblasty - Characteristic in which a plant has small changes in leaf size, shape, and growth habit between juvenile and adult stages.
Heteroblasty - Charactistic in which a plant has marked changes in leaf size, shape, and growth habit between juvenile and adult stages.

Leaf terminology

Shape

Margins (edge)

The leaf margin is characteristic for a genus and aids in determining the species.

entire: even; with a smooth margin; without toothing
ciliate: fringed with hairs
crenate: wavy-toothed; dentate with rounded teeth, such as Fagus
Beech

Beech is a genus of ten species of deciduous trees in the family Fagaceae, native to temperate Europe and North America.The leaf of beech trees are entire or sparsely toothed, from 5–15 cm long and 4–10 cm broad....
(beech)
dentate: toothed, such as Castanea
Chestnut

Chestnut , is a genus of eight or nine species of deciduous trees and shrubs in the Beech family Fagaceae, native to temperate climate regions of the Northern Hemisphere....
(chestnut)

coarse-toothed: with large teeth
glandular toothed: with teeth that bear glands.

denticulate: finely toothed
doubly toothed: each tooth bearing smaller teeth, such as Ulmus
Elm

Elms are deciduous and semi-deciduous trees comprising the genus Ulmus, family Ulmaceae. Elms first appeared in the Miocene period about 40 million years ago....
(elm)
lobate: indented, with the indentations not reaching to the center, such as many Quercus
Oak

The term oak can be used as part of the common name of any of about 400 species of trees and shrubs in the genus Quercus , which are listed in the List of Quercus species, and some related genera, notably Lithocarpus....
(oaks)

palmately lobed: indented with the indentations reaching to the center, such as Humulus
Hop (plant)

Humulus, is a small genus of flowering plants, native to the temperate Northern Hemisphere. The female flowers often called cones, of one species are called hops, and are used as flavoring and Food additive#Categoriess, especially for brewing beer....
(hop).

serrate: saw-toothed with asymmetrical teeth pointing forward, such as Urtica
Nettle

Nettle is the common name for between 30-45 species of flowering plants of the genus Urtica in the family Urticaceae, with a cosmopolitan distribution though mainly temperate distribution....
(nettle)
serrulate: finely serrate
sinuate: with deep, wave-like indentations; coarsely crenate, such as many Rumex
Rumex

The docks and sorrels, genus Rumex Carolus Linnaeus, are a genus of about 200 species of Annual plant, Biennial plant and perennial plant herbs in the buckwheat family Polygonaceae....
(docks)
spiny: with stiff, sharp points, such as some Ilex
Holly

Holly is a genus of approximately 600 species of flowering plants in the family Aquifoliaceae, and the only living genus in that family....
(hollies) and Cirsium
Thistle

Thistle is the common name of a group of flowering plants characterised by leaf with sharp prickles on the margins, mostly in the plant family Asteraceae....
(thistles).

Tip of the leaf

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, as a continuation of the midrib; tipped with a mucro.
mucronulate: mucronate, but with a smaller spine.
obcordate: inversely heart-shaped, deeply notched at the top.
obtuse: rounded or blunt
truncate: ending abruptly with a flat end, that looks cut off.

Base of the leaf

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.

Surface of the leaf

The surface of a leaf can be described by several botanical terms:

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.
papillate, 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, 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

Phyllosphere

The phyllosphere is a term used in microbiology to refer to leaf surfaces or total above-ground surfaces of a plant as a habitat for microorganisms....
.

Hairiness (trichomes)

"Hairs" on plants are properly called trichome

Trichome

glabrous: no hairs of any kind present.
arachnoid, 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.
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, lanose: with woolly hairs.
pilose: with soft, clearly separated hairs.
puberulent, puberulous: with fine, minute hairs.
pubescent: with soft, short and erect hairs.
scabrous, 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, 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.

villous: with long and soft hairs, usually curved.
woolly: with long, soft and tortuous or matted hairs.

Adaptations

In the course of evolution, leaves adapted to different environment

Environment (biophysical)

The biophysical environment is the symbiosis between the physics environment and the biological life forms within the environment, and include all variables that comprise the Earth's biosphere....
s in the following ways:

A certain surface structure avoids moistening by rain and contaminations (Lotus effect
Lotus effect

The Lotus effect refers to the very high water repellency exhibited by the leaves of the lotus flower .Dirt particles are picked up by water droplets due to a complex micro- and nanoscopic architecture of the surface which enables minimization of adhesion....
).
Sliced leaves reduce wind resistance.
Hairs on the leaf surface trap humidity in dry climates and create a large boundary layer and reduce water loss.
Wax
Wax

Wax has traditionally referred to a substance that is secreted by bees and used by them in constructing their honeycombs.It is an imprecisely defined term generally understood to be a substance with properties similar to beeswax, namely...
y leaf surfaces reduce water loss.
Shiny leaves deflect the sun
Sun

The Sun , a G V star, is the star at the center of the Solar System. The Earth and other matter orbit the Sun, which by itself accounts for about 98.6% of the Solar System's mass....
's rays.
Reductions of leaf sizes accompanied by a transfer of the photosynthetic functions to the stems reduce water loss.
In more or less opaque or buried in the soil leaves, translucent windows filter the light before the photosynthetis takes place at the inner leaf surfaces (e.g. Fenestraria
Fenestraria

Fenestraria is a monotypic genus of succulent plants in the family Aizoaceae. The species is also called babies toes or window plant....
).
Thicker leaves store water (leaf succulents).
Aromatic oils, poisons or pheromones produced by leaf borne glands deter herbivores (e.g. eucalypts).
Inclusions of crystalline minerals deter herbivores.
A transformation into petal
Petal

A petal is one member or part of the Corolla of a flower. The corolla is the name for all of the petals of a flower; the inner perianth whorl, term used when this is not the same in appearance as the outermost whorl and is used to attract pollinators based on its advertising coloration....
s attracts pollinators.
A transformation into spines
Spine (botany)

Spines are leaves that have been modified into cylindrical, hard structures with sharp ends. They are occasionally called thorn , which is incorrect ....
protects the plants (e.g. cactus
Cactus

A cactus is any member of the spine plant family Cactaceae, native to the Americas. They are often used as ornamental plants, but some are also Crop plants....
).
A transformation into insect traps helps feeding the plants (carnivorous plant
Carnivorous plant

Carnivorous plants are plants that derive some or most of their nutrients from trapping and consuming animals or protozoans, typically insects and other arthropods....
s).
A transformation into bulb
Bulb

A bulb is an underground vertical shoot that has modified leaf that are used as food storage organs by a dormancy plant.A bulb's leaf bases generally do not support leaves, but contain food reserves to enable the plant to survive adverse conditions....
s helps storing food and water (e.g. onion
Onion

Onion is a term used for many plants in the genus Allium. They are known by the common name "onion" but, used without qualifiers, it usually refers to Allium cepa....
).
A transformation into tendril
Tendril

In botany, a tendril is a specialized Plant stem, leaf or Petiole with a threadlike shape that is used by climbing plants for support and attachment, generally by twining around whatever it touches....
s allows the plant to climb (e.g. pea
Pea

A pea is most commonly the small spherical seed or the seed-pod of the legume Pisum sativum. Each pod contains several peas. Although treated as a vegetable in cooking, it is botanically a fruit....
).
A transformation into bract
Bract

In botany, a bract is a modified or specialized leaf. Bracts are ordinarily associated with reproductive structures . They are ordinarily reduced in size relative to foliage leaves, or of a different color or texture from foliage leaves, or both....
s and pseudanthia
Pseudanthium

A pseudanthium or flower head is a special type of inflorescence, in which several flowers are grouped together to form a flower-like structure....
(false flowers) replaces normal flower structures if the true flowers are extremely reduced (e.g. Spurge
Spurge

Euphorbia is a genus of plants belonging to the family Euphorbiaceae. Consisting of about 2160 species, Euphorbia is one of the most diverse genera in the plant kingdom....
s).

Interactions with other organisms

mimic leaves (Kallima inachus

Kallima inachus

The Orange Oakleaf or Dead Leaf Kallima inachus is a Nymphalidae butterfly found in tropical Asia from India to Japan. With wings closed, it closely resembles a dry leaf with dark veins and is a spectacular example of camouflage....
shown).]] Although not as nutritious as other organs such as fruit, leaves provide a food source for many organisms. Animals which eat leaves are known as folivore

Folivore

In zoology, a folivore is a herbivore that specializes in eating leaves. Mature leaves contain a high proportion of hard-to-digest cellulose and relatively little energy....
s. The leaf is one of the most vital parts of the plant, and plants have evolved protection against folivores such as tannin

Tannin

Tannins are astringent, bitter plant polyphenols that either bind and Precipitation or shrink proteins. The astringency from the tannins is what causes the dry and puckery feeling in the mouth following the consumption of red wine or an unripened fruit....
s, chemicals which hinder the digestion of proteins and have an unpleasant taste. Some animals have cryptic

Crypsis

File:Agama aculeata.jpgIn ecology, crypsis is the ability of an organism to avoid observation. A form of antipredator adaptation, methods range from camouflage, nocturnality, wiktionary:subterranean lifestyle, Transparency , or Batesian mimicry....
adaptations to avoid their own predators, for example some caterpillars will create a small home in the leaf by folding it over themselves, while other herbivores and their prey mimic the appearance of the leaf. Some insects, such as the katydid, take this even further, moving from side to side much like a leaf does in the wind.

Bibliography

Leaves: The formation, charactistics and uses of hundred of leaves in all parts of the world by Ghillean Tolmie Prance. 324 photographic plates in black and white, and colour by Kjell B Sandved 256 pages

Footnotes

External links

Leaf structure and transpiration resource for teens.

Leaf

Leaf anatomy

Epidermis

Mesophyll

Veins

Leaf morphology

Basic leaf types

Arrangement on the stem

Divisions of the lamina (blade)

Characteristics of the petiole

Venation (arrangement of the veins)

Leaf morphology changes within a single plant

Leaf terminology

Shape

Margins (edge)

Tip of the leaf

Base of the leaf

Surface of the leaf

Hairiness (trichomes)

Adaptations

Interactions with other organisms

Bibliography

Footnotes

See also

External links