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The leaves of a Beech tree.

3D rendering of a µCT scan of a leaf piece, resolution circa 40 µm/voxel.

Lichen Dolichousnea longissima. The photosynthetic appendages on the strands are leaf-like in appearance and function but ontogenically are not leaves.

A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants.^[1][2]

Typically a leaf is a thin, flattened organ borne above ground and specialized for photosynthesis, but many types of leaves are adapted in ways almost unrecognisable in those terms: some are not flat (for example many succulent leaves and conifers), some are not above ground (such as bulb scales), and some are without major photosynthetic function (consider for example cataphylls, spines, and cotyledons).

Conversely, many structures of non-vascular plants, or even of some lichens, which are not plants at all (in the sense of being members of the kingdom Plantae), do look and function much like leaves. Furthermore, several structures found in vascular plants look like leaves but are not actually leaves; they differ from leaves in their structures and origins. Examples include phyllodes, cladodes, and phylloclades.^[2]

General nature of leaves[link]

Typically leaves are flat and thin, thereby maximising the surface area directly exposed to light and promoting photosynthetic function. Externally they commonly are arranged on the plant in such ways 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 Eucalyptus.

Likewise, 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. Most leaves have stomata, which open or narrow to regulate the exchange of carbon dioxide, oxygen, and water vapour with the atmosphere.

In contrast however, some leaf forms are adapted to modulate the amount of light they absorb to avoid or mitigate excessive heat, ultraviolet damage, or desiccation, or to sacrifice light-absorption efficiency in favour of protection from herbivorous enemies. Among these forms the leaves of many xerophytes are conspicuous. For such plants their major constraint is not light flux or intensity, but heat, cold, drought, wind, herbivory, and various other hazards.^[3] Typical examples among such strategies are so-called window plants such as Fenestraria species, some Haworthia species such as Haworthia tesselata and Haworthia truncata^[4] and Bulbine mesembryanthemoides.^[5]

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, 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.^[6] 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.

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 are richer in protein, minerals, and sugars, than say, woody stem tissues. Accordingly leaves are prominent in the diet of many animals. This is true for humans, for whom leaf vegetables commonly are food staples.

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.

Deciduous plants in frigid or cold temperate regions typically shed their leaves in autumn, whereas in areas with a severe dry season, some plants may shed their leaves until the dry season ends. In either case the shed leaves may be expected to contribute their retained nutrients to the soil where they fall.

In contrast, many other non-seasonal plants, such as palms and conifers, retain their leaves for long periods; Welwitschia retains its two main leaves throughout a lifetime that may exceed a thousand years.

Not all plants have true leaves. Bryophytes (e.g., mosses and liverworts) are non-vascular plants, and, although they produce flattened, leaf-like structures that are rich in chlorophyll, these organs differ morphologically from the leaves of vascular plants; For one thing, they lack vascular tissue. Vascularised leaves first evolved following the Devonian period, when carbon dioxide concentration in the atmosphere dropped significantly. This occurred independently in two separate lineages of vascular plants: the microphylls of lycophytes and the euphylls ("true leaves") of ferns, gymnosperms, and angiosperms. Euphylls are also referred to as macrophylls or megaphylls ("large leaves").

Large-scale features (leaf morphology)[link]

A structurally complete leaf of an angiosperm consists of a petiole (leaf stalk), a lamina (leaf blade), and stipules (small structures located to either side of the base of the petiole). Not every species produces leaves with all of these structural components. In certain 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 morphology.

The petiole mechanically links the leaf to the plant and provides the route for transfer of water and sugars to and from the leaf. The lamina is typically the location of the majority of photosynthesis.

Anatomy[link]

This section requires expansion.

Medium scale features[link]

Leaves are normally extensively vascularised and are typically covered by a dense network of xylem, which supply water for photosynthesis, and phloem, which remove the sugars produced by photosynthesis. Many leaves are covered in trichomes (small hairs) which have a diverse range of structures and functions.

Small-scale features[link]

A leaf is a plant organ and is made up of a collection of tissues in a regular organisation. The major tissue systems present are:

1. The epidermis that covers the upper and lower surfaces
2. The mesophyll inside the leaf that is rich in chloroplasts (also called chlorenchyma)
3. The arrangement of veins (the vascular tissue)

These three tissue systems typically form a regular organisation at the cellular scale.

Major leaf tissues[link]

Epidermis[link]

SEM image of Nicotiana alata leaf's epidermis, 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 forms the boundary separating the plant's inner cells from the external world. The epidermis serves several functions: protection against water loss by way of transpiration, regulation of gas exchange, secretion of metabolic 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 (epidermal cells lack chloroplasts) and coated on the outer side with a waxy cuticle that prevents water loss. 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 tissue includes several differentiated cell types: epidermal cells, epidermal hair cells (trichomes) cells in the stomate complex; guard cells and subsidiary cells. The epidermal cells are the most numerous, largest, and least specialized and form the majority of the epidermis. These are typically more elongated in the leaves of monocots than in those of dicots.

The epidermis is covered with pores called stomata, 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. Opening and closing of the stoma complex regulates the exchange of gases and water vapor between the outside air and the interior of the leaf and plays an important role in allowing photosynthesis without letting the leaf dry out. In a typical leaf, the stomata are more numerous over the abaxial (lower) epidermis than the adaxial (upper) epidermis and more numerous in plants from cooler climates.

Mesophyll[link]

Most of the interior of the leaf between the upper and lower layers of epidermis is a parenchyma (ground tissue) or chlorenchyma tissue called the mesophyll (Greek for "middle leaf"). This assimilation 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 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 of carbon dioxide. This separation must be minimal to afford capillary action 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, which are connected to the 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 (thin-walled cells separated by large gas-filled spaces). Their stomata are situated at the upper surface.

Leaves are normally green in color, which comes from chlorophyll found in plastids in the chlorenchyma cells. Plants that lack chlorophyll cannot photosynthesize.

Veins[link]

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. They are typical examples of pattern formation through ramification. The pattern of the veins is called venation.

The veins are made up of:

• Xylem: tubes that bring water and minerals from the roots into the leaf.
• Phloem: tubes that usually move sap, with dissolved sucrose, produced by photosynthesis in the leaf, out of the leaf.

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 pith or sheath, which usually includes some structural collenchyma tissue.

Seasonal leaf loss[link]

Leaves shifting color in 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. After the leaf is shed, a leaf scar develops 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 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.^[7]

Morphology[link]

The Citrus 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, and botanists have developed a rich terminology 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 Wikibooks.

Basic types[link]

Leaves of the White Spruce (Picea glauca) are needle-shaped and their arrangement is spiral

• Ferns have fronds
• Conifer leaves are typically needle-, awl-, or scale-shaped
• Angiosperm (flowering plant) leaves: the standard form includes stipules, a petiole, and a lamina
• Lycophytes have microphyll leaves.
• Sheath leaves (type found in most grasses)
• Other specialized leaves (such as those of Nepenthes)

Arrangement on the stem[link]

Different terms are usually used to describe leaf placement (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.

• Alternate – leaf attachments are singular at nodes, and leaves alternate direction, to a greater or lesser degree, along the stem.
• Opposite – Two structures, one on each opposite side of the stem, typically leaves, branches, or flower parts. 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

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 a limit close to 360° x 34/89 = 137.52 or 137° 30', an angle known in mathematics as the golden angle. In the series, the numerator 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 blade[link]

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 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 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. The middle vein of a compound leaf or a frond, when it is present, is called a rachis.

• Palmately compound leaves have the leaflets radiating from the end of the petiole, like fingers off the palm of a hand, e.g. Cannabis (hemp) and Aesculus (buckeyes).
• Pinnately compound leaves have the leaflets arranged along the main or mid-vein.
  • odd pinnate: with a terminal leaflet, e.g. Fraxinus (ash).
  • even pinnate: lacking a terminal leaflet, e.g. Swietenia (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 (silk tree).
• trifoliate (or trifoliolate): a pinnate leaf with just three leaflets, e.g. Trifolium (clover), Laburnum (laburnum).
• pinnatifid: pinnately dissected to the central vein, but with the leaflets not entirely separate, e.g. Polypodium, some Sorbus (whitebeams). In pinnately veined leaves the central vein in known as the midrib.

Characteristics of the petiole[link]

The overgrown petioles of Rhubarb (Rheum rhabarbarum) are edible.

Petiolated leaves have a petiole (leaf 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 the case, the leaves are called "perfoliate", such as in Claytonia perfoliata. In peltate leaves, the petiole attaches to the blade inside from the blade margin.

In some Acacia 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, present on the leaves of many dicotyledons, 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 roses and beans), 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, or sheath-formed stipules, e.g. rhubarb,
  • encircling the petiole base
  • interpetiolar : between the petioles of two opposite leaves.
  • intrapetiolar : between the petiole and the subtending stem

Venation[link]

Branching veins on underside of taro leaf

The venation within the bract of a Lime tree.

The lower epidermis of Tilia × europaea

Palmate-veined leaf

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 (also called pinnate-netted, penniribbed, penninerved, or penniveined) – 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) dicotyledons.
• Three main veins branch at the base of the lamina and run essentially parallel subsequently, as in Ceanothus. A similar pattern (with 3-7 veins) is especially conspicuous in Melastomataceae.
• Palmate-netted, palmate-veined, fan-veined; several main veins diverge from near the leaf base where the petiole attaches, and radiate toward the edge of the leaf, e.g. most Acer (maples).
• Parallel-veined, parallel-ribbed, parallel-nerved, penniparallel – veins run parallel for the length of the leaf, from the base to the apex. Commissural veins (small veins) connect the major parallel veins. Typical for most monocotyledons, such as grasses.
• Dichotomous – There are no dominant bundles, with the veins forking regularly by pairs; found in Ginkgo and some pteridophytes.

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, which are monocots, e.g. Paris quadrifolia (True-lover's Knot).

Morphology changes within a single plant[link]

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

Terminology[link]

Chart illustrating some leaf morphology terms

A portion of a coriander leaf

Shape[link]

Edge (margin)[link]

• ciliate: fringed with hairs
• crenate: wavy-toothed; dentate with rounded teeth, such as Fagus (beech)
• crenulate finely or shallowly crenate
• dentate: toothed, such as Castanea (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)
• entire: even; with a smooth margin; without toothing
• lobate: indented, with the indentations not reaching to the center, such as many Quercus (oaks)
  • palmately lobed: indented with the indentations reaching to the center, such as Humulus (hop).
• serrate: saw-toothed with asymmetrical teeth pointing forward, such as Urtica (nettle)
• serrulate: finely serrate
• sinuate: with deep, wave-like indentations; coarsely crenate, such as many Rumex (docks)
• spiny or pungent: with stiff, sharp points, such as some Ilex (hollies) and Cirsium (thistles).

Tip[link]

Leaves showing various morphologies. Clockwise from upper left: tripartite lobation, elliptic with serrulate margin, peltate with palmate venation, acuminate odd-pinnate (center), pinnatisect, lobed, elliptic with entire margin

• 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[link]

• 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[link]

• 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, 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[link]

Common Mullein (Verbascum thapsus) leaves are covered in dense, stellate trichomes.

Scanning electron microscope image of trichomes on the lower surface of a Coleus blumei (coleus) leaf.

"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.

Adaptations[link]

The embedded lists in this article may contain items that are not encyclopedic. Please help out by removing such elements and incorporating appropriate items into the main body of the article. (February 2008)

Poinsettia bracts are leaves which have evolved red pigmentation in order to attract insects and birds to the central flowers, an adaptive function normally served by petals (which are themselves leaves highly modified by evolution).

In the course of evolution, leaves have adapted to different environments in the following ways:

• A certain surface structure avoids moistening by rain and contamination (See Lotus effect).
• Sliced leaves reduce wind resistance.
• Hairs on the leaf surface trap humidity in dry climates and create a boundary layer reducing water loss.
• Waxy leaf surfaces reduce water loss.
• Large surface area provides large area for sunlight and shade for plant to minimize heating and reduce water loss.
• In more or less opaque or buried in the soil leaves, translucent windows filter the light before the photosynthesis takes place at the inner leaf surfaces (e.g. Fenestraria).
• Succulent leaves store water and organic acids for use in CAM photosynthesis.
• Aromatic oils, poisons or pheromones produced by leaf borne glands deter herbivores (e.g. eucalypts).
• Inclusions of crystalline minerals deter herbivores (e.g. silica phytoliths in grasses, raphides in Araceae).
• Petals attracts pollinators.
• Spines protect the plants (e.g. cacti).
• Insect traps feed the plants directly (see carnivorous plants).
• Bulbs store food and water (e.g. onions).
• Tendrils allow the plant to climb (e.g. peas).
• Bracts and pseudanthia (false flowers) replace normal flower structures when the true flowers are greatly reduced (e.g. Spurges).

Interactions with other organisms[link]

Some insects mimic leaves (Kallima inachus shown)

A girl playing with leaves

Leaf after being eaten by Caterpillar

Dew on a leaf

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 folivores. The leaf is one of the most vital parts of the plant, and plants have evolved protection against folivores such as tannins, chemicals which hinder the digestion of proteins and have an unpleasant taste.

Some animals have cryptic 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[link]

• 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^[8]

Footnotes[link]

See also[link]

• Abscission – loss of leaves
• Cladode - a flattened photsynthetic stem, if very leaf-like then it is called a Phylloclade
• Cladophyll – a stem-like leaf part (synonym: phyllode)
• Evolution of leaves
• Guttation – beads of fluid forming at leaf margins
• Leaf area index
• Leaf protein concentrate
• Leaf Sensor – a device that measures the moisture level in plant leaves
• Vernation – sprouting of leaves, also the arrangement of leaves in the bud

External links[link]

• Media related to Leaves at Wikimedia Commons
• The Wiktionary entry for leaf
• VASCULAR PLANT SYSTEMATICS Section B. General Characters and Character States: Position and Arrangement
• Science aid: Leaf Leaf structure and transpiration resource for teens.

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Eva Marie Cassidy (February 2, 1963 – November 2, 1996) was an American vocalist known for her interpretations of jazz, blues, folk, gospel, country and pop classics. In 1992 she released her first album, The Other Side, a set of duets with go-go musician Chuck Brown, followed by a live solo album, Live at Blues Alley in 1996. Although she had been honored by the Washington Area Music Association, she was virtually unknown outside her native Washington, D.C., when she died of melanoma (skin cancer) in 1996.

Four years later, Cassidy's music was brought to the attention of British audiences when her version of "Over the Rainbow" was played by Terry Wogan on BBC Radio 2. Following the overwhelming response, a camcorder recording of "Over the Rainbow", taken at Blues Alley in Washington, was shown on BBC Two's Top of the Pops 2. Shortly afterwards, the compilation album Songbird climbed to the top of the UK Albums Charts, almost three years after its initial release. The chart success in the United Kingdom and Ireland led to increased recognition worldwide; her posthumously released recordings, including three UK number 1s, have sold more than ten million copies.^[1] Her music has also charted top 10 positions in Australia, Germany, Sweden, Norway and Switzerland.^[2]

Biography[link]

Early life[link]

Born on February 2, 1963, at the Washington Hospital Center,^[3] Cassidy grew up in Oxon Hill and later Bowie, Maryland, suburbs of Washington, D.C.. She was the third of four children born to Hugh and Barbara Cassidy. Her father, a retired teacher, sculptor, musician, Powerlifter and former army medic, is of Scottish and Irish descent, while her German-born mother was a horticulturist.^[2][4][5] From an early age, Cassidy displayed interest in art and music. When she was nine, her father taught her to play the guitar and she began to play and sing at family gatherings.^[4]

At age 11, Cassidy began singing and playing guitar in a Washington area band called Easy Street.^[6] This band performed in a variety of styles at weddings, corporate parties and pubs. Due to her shyness, she struggled with performing in front of strangers. While a student at Bowie High School, she sang with a local band called Stonehenge.^[4] During the summer of 1983, Cassidy sang and played guitar six days a week at the theme park Wild World.^[4] Her younger brother Dan, a fiddler, was also a member of this working band. She enrolled in art classes at a community college but dropped out after finding them unhelpful.^[7]

Throughout the 1980s, Cassidy worked with several other bands, including the techno-pop band Characters Without Names. During this period, Cassidy also worked as a propagator at a plant nursery and as a furniture painter. In her free time, she explored other artistic expressions including painting, sculpting and jewelry design.^[7] Despite holding a belief in God, Cassidy was not part of any organized religion.^[8]

Music career[link]

In 1986, Cassidy was asked by Stonehenge guitarist and high school friend, David Lourim, to lend her voice to his music project, Method Actor.^[9] This brought her to Black Pond Studios, where she met bassist and recording engineer Chris Biondo. Biondo helped her find work as a session singer and later introduced her to Al Dale, who would become her manager. She sang back-ups for various acts, from go-go rhythm and blues band Experience Unlimited to rapper E-40.^[10] Biondo and Cassidy, who were in a romantic relationship for a time, formed the five-piece "Eva Cassidy Band" with Lenny Williams, Keith Grimes and Raice McLeod in 1990. They began to perform frequently in the Washington area.^[4]

	"Over the Rainbow" noicon One of the changes Cassidy made to "Over the Rainbow" includes singing the opening word "somewhere" on the same high A flat, rather than with an octave jump of the Judy Garland version.
Problems listening to this file? See media help.

	"Stormy Monday" noicon Cassidy's arrangement of T-Bone Walker's popular blues song.
Problems listening to this file? See media help.

In 1992, Biondo played a tape of Cassidy's voice for Chuck Brown, the "Godfather of go-go".^[11] It resulted in the duet album The Other Side featuring performances of classic songs such as "Fever", "God Bless the Child," and what would later become Cassidy's signature song, "Over the Rainbow". The album was released and distributed in 1992 by Liaison Records, the label that also released Brown's Go-go albums. Brown originally intended to record a single duet with Cassidy for his next solo album, but this was postponed due to ongoing negotiations between Dale and other labels for a solo deal.^[10][12] Cassidy's unwillingness to narrow her stylistic focus to one genre hindered her chances of securing a deal.^[13][14] After talks broke down, the two decided to record their own duet album. As a duo, they performed at the Columbia Arts Festival and opened for acts like Al Green and The Neville Brothers.^[10]

In 1993, Cassidy was honored by the Washington Area Music Association with a Wammie award for the Vocalist Jazz/Traditional category.^[15] The next year she was invited to perform at the event and chose to sing "Over the Rainbow". A Washington Times review of the event called her performance "a show-stopper".^[16] She took home two Wammies that night, again for Vocalist Jazz/Traditional and also for Roots Rock/Traditional R&B.^[15] For a brief period that year, Cassidy signed a deal with Blue Note Records to pair up with pop-jazz band Pieces of a Dream to release an album and tour the country. She sang two tracks in a mainly instrumental album. It was a musically unsatisfying experience for her.^[10]

After having a potential contract with Apollo Records collapse when the label went bankrupt, Biondo and Dale decided that she should release her own live album.^[10] In January 1996, the material for Live at Blues Alley was recorded over a two-day period at Blues Alley, Washington, D.C. Due to a technical glitch on the first night of recording,^[17] only the second night's recording was usable. Unhappy with the way she sounded due to a cold, she was reluctant to release the album. She eventually relented, on the condition that the studio track "Oh, Had I a Golden Thread", Cassidy's favorite song,^[18] would be included in the release, and that they start working on a follow-up studio album.^[7][10] Her apprehension appeared unfounded as local reviewers and the public responded positively.^[7] The Washington Post commented that "she could sing anything — folk, blues, pop, jazz, R&B, gospel — and make it sound like it was the only music that mattered."^[11] The subsequent studio album she worked on was released as Eva by Heart posthumously in 1997. In the liner notes of Eva by Heart, critic Joel E. Siegel described Cassidy as "one of the greatest voices of her generation."^[7]

Death[link]

In 1993, Cassidy had a malignant mole removed from her back. Three years later, during a promotional event for the Live at Blues Alley album in July 1996, Cassidy noticed an ache in her hips, which she attributed to stiffness from painting murals while perched atop a stepladder.^[11] The pain persisted and a few weeks later, X-rays revealed that the melanoma had spread to her lungs and bones. Her doctors estimated she had three to five months to live. Cassidy opted for aggressive treatment, but her health deteriorated rapidly. In the early fall, at a benefit concert for her at the Bayou, she made her final public appearance, closing the set with "What a Wonderful World" in front of an audience of friends, fans and family. Additional chemotherapy was uneffective, and within six weeks she had died.^[2][11][19]

Cassidy died on November 2, 1996, at her family home in Bowie, Maryland. She was 33. In accordance with her wishes, her body was cremated and the ashes were scattered on the lake shores of St. Mary's River Watershed Park, a nature reserve near Callaway, Maryland.^[2]

Posthumous recognition[link]

After Cassidy's death, local folk singer Grace Griffith introduced the Blues Alley recording to Bill Straw from her label, Blix Street Records.^[19] Straw approached the Cassidy family to put together a new album. In 1998, a compilation of tracks from Cassidy's three released recordings was assembled into the CD Songbird. This CD lingered in relative obscurity for two years until being given airplay by Terry Wogan on his wide-reaching BBC Radio 2 show Wake Up to Wogan, following recommendation by his producer Paul Walters. The album sold more than 100,000 copies in the following months.^[2] The New York Times spoke of her "silken soprano voice with a wide and seemingly effortless range, unerring pitch and a gift for phrasing that at times was heart-stoppingly eloquent."^[19]

Before Christmas of 2000, Top Of The Pops 2 aired a video of Cassidy performing "Over the Rainbow", which resulted in Songbird climbing steadily up the UK charts over the next few weeks. Just as ITV's Tonight with Trevor McDonald aired a feature on Cassidy, the album topped the chart.^[20] Shot at Blues Alley by a friend with a camcorder the same night the album was recorded,^[2] the video became the most requested video ever shown on Top Of The Pops 2.^[21] "There's an undeniable emotional appeal in hearing an artist who you know died in obscurity singing a song about hope and a mystical world beyond everyday life", wrote The Guardian.^[22]

Paul McCartney and Eric Clapton were among her new-found fans. Jazz critic Ted Gioia writes, "you might be tempted to write off the 'Cassidy sensation' [...] as a response to the sad story of the singer's abbreviated life rather than as a measure of her artistry. But don't be mistaken, Cassidy was a huge talent, whose obscurity during her lifetime was almost as much a tragedy as her early death."^[23] Songbird has since achieved significant chart success throughout Europe and six times platinum status in the UK.^[2][24] Although still relatively unknown in the United States at that time, the album would eventually be certified gold in the U.S. as well.^[25]

In May 2001, ABC's Nightline in the United States broadcast a well-received short documentary about Cassidy.^[26] Over the weekend, all five of Cassidy's albums occupied Amazon.com's best sellers list top spots.^[27] The Nightline episode has since been rebroadcast three times due to popular demand.^[28] Producer Leroy Sievers has said that it is "probably the most popular Nightline ever".^[29] In December, a nine-minute segment on NPR resulted in a similar sales surge, with five of the top seven spots going to Cassidy.^[4] A rebroadcast of the Tonight with Trevor McDonald feature on Cassidy in Britain also bumped up sales.^[4][30]

Since Songbird, several other CDs with original material have been released: Time After Time (2000), Imagine (2002) and American Tune (2003). 2008 saw the release of another new album titled Somewhere. Unlike previous albums, which consisted solely of cover songs, this release contains two original songs co-written by Cassidy. An acoustic album titled Simply Eva was released in January 2011.

Together with word of mouth and internet fansites, online commerce has played a big role in Cassidy's success.^[31][32] This point was further affirmed when in 2005, Amazon.com released a list of its top 25 best-selling musicians, which placed Cassidy in fifth position, behind The Beatles, U2, Norah Jones and Diana Krall,^[33] and far ahead of Elvis Presley and several other well-known stars.^[34]

In 2004, during the gala opening of the Bowie Center for the Performing Arts, the Bowie Regional Arts Vision Association, Inc. (BRAVA) dedicated the Star's Dressing Room to Eva. Following a moving tribute to Eva, Chuck Brown took the stage and performed his duet "with" Eva as her photos and video appeared in the background.

Unofficial recordings[link]

A collection of previously unreleased studio recordings from 1987 to 1991, was released in 2000 as No Boundaries. This release was not endorsed by the Cassidy family^[2] and was released under a different label. An allmusic review of the album stated that even "a gifted vocalist like Eva Cassidy can only do so much with bad material".^[35] In 2002, the self titled 1988 album by the band Method Actor, which featured Cassidy, was re-released by the band's guitarist and producer David Lourim with Cassidy's name displayed prominently on the cover. The Cassidy family and Blix Street Records filed a lawsuit against Lourim, claiming that Cassidy's name was used in a misleading fashion and that Blix Street has exclusive rights to her recordings.^[36] Lourim had Cassidy's written permission to release the album and eventually the cover was changed to look like the original LP album while already released copies were affixed with a sticker indicating that they are not solo Eva Cassidy albums.^[37][38]

A bootleg recording which has been in circulation is called Live at Pearl's. It was recorded at Pearl's Restaurant in Annapolis, Maryland in 1994. Copies of the recording were circulated among friends and families after her death. Some of the songs on the recording are also on Imagine and American Tune.^[39] Another recording, featuring Mick Fleetwood on drums and recorded at his restaurant in Alexandria, Virginia called Fleetwood's in the early 1990s, was in the possession of Niki Lee - the former wife of pianist Lenny Williams - who discovered it in her garage and attempted to sell it on eBay in 2008.^[40]

In popular media[link]

In 2001, a book titled Songbird: Eva Cassidy: Her Story By Those Who Knew Her, on the life and work of Cassidy based on interviews with close family and associates was released in the UK. The hardcover edition has since sold in excess of 100,000 copies. A U.S. edition published by Gotham Books was released in late 2003 and includes two additional chapters on her influences and success in the US. Her life story has also been adapted into a musical^[41] and also a Broadway piece for cancer benefit.^[42]

At the 2002 Winter Olympics gala, and later on tour, figure skater Michelle Kwan brought Cassidy's music to a new audience when she skated to a recording of "Fields of Gold". Kwan's part in exposing the music of Cassidy to the international and American public led Cassidy's label to present her a gold record from the certification of Songbird.^[43] Subsequently, other figure skaters such as Kristi Yamaguchi, Sarah Hughes and Kimmie Meissner have used Cassidy's music in their routines.

Anglo-Georgian singer Katie Melua is a keen fan of Cassidy.^[44] Her debut album "Call Off the Search" contained the song "Faraway Voice", written in Cassidy's memory.^[44] Melua has also performed Cassidy's arrangement of "Anniversary Song" in concert.^[44] On Christmas Eve 2006, she performed alongside video footage of Cassidy singing Over The Rainbow on BBC One's "Duet Impossible".^[45] One year later, Cassidy's "What A Wonderful World" was spliced together with new vocals by Melua and released as a single exclusively at the British retail chain Tesco. It debuted at #1 on the UK Singles chart on December 16. All profits from the single went to the British Red Cross.^[46] Irish singer Chris de Burgh has stated that his song "Songbird" from his album The Road to Freedom was written in honour of Cassidy. Singer Mary Chapin Carpenter made reference to Cassidy in the song "My Heaven" on the album Between Here and Gone: "More memories than my heart can hold, when Eva's singing 'Fields of Gold'."

In 2008, Cassidy's recording of "Autumn Leaves" was used by the Canadian National Professional Latin Champions, Andre and Natalie Paramonov, when they competed in America's Ballroom Challenge as finalists in the International Latin Competition.

The first film to feature an Eva Cassidy recording was Flight of Fancy starring Dean Cain. Since then her music has appeared in various film and TV series including the Dawson's Creek season four episode titled "The Graduate," Judging Amy, Joe Somebody, Love Actually, Maid in Manhattan, The Man From Elysian Fields, Alpha Dog and Smallville. Cassidy's arrangement of "Over the Rainbow" is a popular cover choice by singing competition contestants, with American Idol season 5 runner-up Katharine McPhee and The X Factor season 3 winner Leona Lewis among the singers. Her interpretation of "Imagine" has been performed by American Idol season 7 runner-up David Archuleta.

In March 2012, Sweden's Caroline Larsson and Bengt Magnusson released an album entitled A Tribute to Eva Cassidy.

Possibility of future film[link]

In late 2007, AIR Productions acquired the rights to produce a film based on Cassidy's life.^[47] It is being produced by Amy Redford (daughter of Robert Redford), Irwin Shapiro and Rick Singer.^[48] In an interview a year earlier, Cassidy's parents suggested Kirsten Dunst or Emily Watson as possible actresses who could play their daughter.^[49]

A documentary on the life, art and music of Cassidy entitled Eva's Song is expected to be in theaters February 2013.^[50]

Discography[link]

Albums[link]

Singles[link]

Bootleg[link]

Videography[link]

References[link]

Notes[link]