Leaf

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The leaves of a Beech tree

In botany, a leaf is an above-ground plant organ specialized for photosynthesis. For this purpose, a brand is about collapsed (laminar) and thin. As an evolutionary trait, the apathy of leaves works to betrayal the chloroplasts to added light and to access the absorption of carbon dioxide at the amount of baptize loss. In the Devonian period, if carbon dioxide assimilation was at several times its present value, plants did not accept leaves or collapsed stems. Abounding bryophytes accept flat, photosynthetic organs, but these are not accurate leaves. Neither are the microphylls of lycophytes. The leaves of ferns, gymnosperms, and angiosperms are abnormally referred to as macrophyll, megaphylls, or euphylls.

Leaves are aswell the sites in a lot of plants breadth transpiration and guttation crop place. Leaves can abundance food and water, and are acclimatized in some plants for added purposes. The commensurable structures of ferns are accurately referred to as fronds. Furthermore, leaves are arresting in the human diet as leaf vegetables.

Anatomy

Leaf in autumn.

Cross breadth of a leaf

A structurally complete brand of an angiosperm consists of a petiole (leaf stalk), a lamina (leaf blade), and stipules (small processes amid to either ancillary of the abject of the petiole). The petiole attaches to the axis at a point alleged the "leaf axil." Not every breed produces leaves with all of the above structural components. In assertive species, commutual stipules are not accessible or are absent altogether. A brand may be absent, or the brand may not be laminar (flattened). The amazing array apparent in brand analysis (anatomy) from breed to breed is presented in detail below beneath Leaf morphology. Periodically (i.e. seasonally, during the autumn), deciduous copse allow their leaves. These leaves again decompose into the soil.

A brand is advised a bulb agency and about consists of the afterward tissues:

1. An epidermis that covers the high and lower surfaces
2. An autogenous chlorenchyma alleged the mesophyll
3. An adjustment of veins (the vascular tissue)

Epidermis

Epidermal cells

The epidermis is the alien band of cells accoutrement the leaf. It forms the abuttals amid the plant's abutting beef from the alien world. The covering serves several functions: aegis adjoin baptize accident by way of transpiration, adjustment of gas exchange, beard of metabolic compounds, and (in some species) assimilation of water. A lot of leaves actualization dorsoventral anatomy: the high (adaxial) and lower (abaxial) surfaces accept somewhat altered architecture and may serve altered functions.

The covering is usually transparent (epidermal beef abridgement chloroplasts) and coated on the alien ancillary with a adhering cuticle that prevents baptize loss. The cuticle is in some cases thinner on the lower covering than on the high epidermis, and is thicker on leaves from dry climates as compared with those from wet climates.

SEM angel of Nicotiana alata leaf's epidermis, assuming trichomes (hair-like appendages) and stomata (eye-shaped slits, arresting at abounding resolution).

The covering tissue includes several differentiated corpuscle types: epidermal cells, bouncer cells, accent cells, and epidermal hairs (trichomes). The epidermal beef are the a lot of numerous, largest, and atomic specialized. These are about added continued in the leaves of monocots than in those of dicots.

The covering is covered with pores alleged stomata, allotment of a stoma circuitous consisting of a pore amidst on anniversary ancillary by chloroplast-containing bouncer cells, and two to four accent beef that abridgement chloroplasts. The stoma circuitous regulates the barter of gases and baptize breath amid the alfresco air and the autogenous of the leaf. Typically, the stomata are added abundant over the abaxial (lower) covering than the adaxial (upper) epidermis.

Mesophyll

Most of the autogenous of the brand amid the high and lower layers of covering is a parenchyma (ground tissue) or chlorenchyma tissue alleged the mesophyll (Greek for "middle leaf"). This assimilation tissue is the primary breadth of photosynthesis in the plant. The articles of photosynthesis are alleged "assimilates".

Palisade cells

In ferns and a lot of beginning plants the mesophyll is disconnected into two layers:

• An high palisade layer of acutely packed, angular continued cells, one to two beef thick, anon below the adaxial epidermis. Its beef accommodate abounding added chloroplasts than the absorptive layer. These continued annular beef are consistently abiding in one to 5 rows. Annular cells, with the chloroplasts abutting to the walls of the cell, can crop optimal advantage of light. The slight break of the beef provides best absorption of carbon dioxide. This break accept to be basal to allow capillary action for baptize distribution. In adjustment to acclimate to their altered ambiance (such as sun or shade), plants had to acclimate this analysis to access optimal result. Sun leaves accept a multi-layered palisade layer, while adumbration leaves or earlier leaves afterpiece to the soil, are single-layered.

Spongy cells

• Beneath the palisade band is the spongy layer. The beef of the absorptive band are added angled and not so acutely packed. There are ample intercellular air spaces. These beef accommodate beneath chloroplasts than those of the palisade layer.

The pores or stomata of the covering accessible into substomatal chambers, abutting to air spaces amid the absorptive band cells.

These two altered layers of the mesophyll are absent in abounding amphibian and marsh plants. Even an covering and a mesophyll may be lacking. Instead for their aerial exchanges they use a constant aerenchyma (thin-walled beef afar by ample gas-filled spaces). Their stomata are anchored at the high surface.

Leaves are commonly green in color, which comes from chlorophyll begin in plastids in the chlorenchyma cells. Plants that abridgement chlorophyll cannot photosynthesize.

Leaves in temperate, boreal, and seasonally dry zones may be seasonally deciduous (falling off or dying for the brutal season). This apparatus to allow leaves is alleged abscission. After the brand is shed, a brand blister develops on the twig. In algid autumns they sometimes change color, and about-face yellow, ablaze orange or red as assorted accent pigments (carotenoids and xanthophylls) are arise if the timberline responds to algid and bargain sunlight by abbreviating chlorophyll production. Red anthocyanin pigments are now anticipation to be produced in the brand as it dies, possibly to affectation the chicken hue larboard if the chlorophyll is absent - chicken leaves arise to allure herbivores such as aphids.¹

Veins

Vein skeleton of a Hydrangea leaf

The veins are the vascular tissue of the brand and are amid in the absorptive band of the mesophyll. They are archetypal examples of pattern formation through ramification. The adjustment of the veins is alleged venation.

The veins are fabricated up of:

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

The xylem about lies over the phloem. Both are anchored in a abutting parenchyma tissue, alleged "pith", with usually some structural collenchyma tissue present.

Morphology

The Citrus brand is articular by the pores and pigments, as able-bodied as the margins.

External brand characteristics (such as shape, margin, hairs, etc.) are important for anecdotic bulb species, and botanists accept developed a affluent terminology for anecdotic brand characteristics. These structures are a allotment of what makes leaves determinant; they abound and accomplish a specific adjustment and shape, again stop. Added bulb locations like stems or roots are non-determinant, and will usually abide to abound as continued as they accept the assets to do so.

Classification of leaves can action through abounding altered apocalyptic schema, and the blazon of brand is usually acclimatized of a species, although some breed aftermath added than one blazon of leaf. The longest blazon of brand is a brand from approach trees, barometer at nine anxiety long. The analogue associated with the description of brand analysis is presented, in illustrated form, at Wikibooks.

Basic types

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

• Ferns accept fronds
• Conifer leaves are about needle-, awl-, or scale-shaped
• Angiosperm (flowering plant) leaves: the accepted anatomy includes stipules, a petiole, and a lamina
• Lycophytes accept microphyll leaves.
• Sheath leaves (type begin in a lot of grasses)
• Other specialized leaves (such as those of Nepenthes)

Arrangement on the stem

Different agreement are usually acclimated to call brand adjustment (phyllotaxis):

The leaves on this bulb are abiding in pairs adverse one another, with alternating pairs at acclimatized angles to anniversary added ("decussate") forth the red stem. Note developing buds in the axils of these leaves.

• Alternate — brand accessories are atypical at nodes, and leaves alternating direction, to a greater or bottom degree, forth the stem.
• Opposite — Two structures, one on anniversary adverse ancillary of the stem, about leaves, branches, or annual parts. Brand accessories are commutual at anniversary node; decussate if, as typical, anniversary alternating brace is rotated 90° advanced forth the stem; or distichous if not rotated, but two-ranked (in the aforementioned geometric flat-plane).
• Whorled — three or added leaves attach at anniversary point or bulge on the stem. As with adverse leaves, alternating whorls may or may not be decussate, rotated by bisected the angle amid the leaves in the coil (i.e., alternating whorls of three rotated 60°, whorls of four rotated 45°, etc.). Adverse leaves may arise circling abreast the tip of the stem.
• Rosulate — leaves anatomy a rosette

As a stem grows, leaves tend to arise abiding about the axis in a way that optimizes crop of light. In essence, leaves anatomy a helix adjustment centred about the stem, either clockwise or counterclockwise, with (depending aloft the species) the aforementioned angle of divergence. There is a regularity in these angles and they chase 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 alternation tends to a absolute abutting to 360° x 34/89 = 137.52 or 137° 30', an angle accepted mathematically as the golden angle. In the series, the numerator indicates the amount of complete turns or "gyres" until a brand arrives at the antecedent position. The denominator indicates the amount of leaves in the arrangement. This can be approved by the following:

• alternate leaves accept an angle of 180° (or 1/2)
• 120° (or 1/3) : three leaves in one circle
• 144° (or 2/5) : 5 leaves in two gyres
• 135° (or 3/8) : eight leaves in three gyres.

Divisions of the blade

A brand with laminar analysis and pinnate venation

Two basal forms of leaves can be declared because the way the brand (lamina) is divided. A simple leaf has an absorbed blade. However, the brand actualization may be formed of lobes, but the gaps amid lobes do not ability to the capital vein. A compound leaf has a absolutely subdivided blade, anniversary leaflet of the brand afar forth a capital or accessory vein. Because anniversary advertisement can arise to be a simple leaf, it is important to admit breadth the brand occurs to analyze a admixture leaf. Admixture leaves are a acclimatized of some families of college plants, such as the Fabaceae. The average attitude of a admixture brand or a frond, if it is present, is alleged a rachis.

• Palmately compound leaves accept the leaflets beaming from the end of the petiole, like fingers off the approach of a hand, e.g. Cannabis (hemp) and Aesculus (buckeyes).
• Pinnately compound leaves accept the leaflets abiding forth the capital or mid-vein.
  • odd pinnate: with a terminal leaflet, e.g. Fraxinus (ash).
  • even pinnate: defective a terminal leaflet, e.g. Swietenia (mahogany).
• Bipinnately compound leaves are alert divided: the leaflets are abiding forth a accessory attitude that is one of several aberration off the rachis. Anniversary advertisement is alleged a "pinnule". The pinnules on one accessory attitude are alleged "pinna"; e.g. Albizia (silk tree).
• trifoliate (or trifoliolate): a pinnate brand with just three leaflets, e.g. Trifolium (clover), Laburnum (laburnum).
• pinnatifid: pinnately dissected to the axial vein, but with the leaflets not absolutely separate, e.g. Polypodium, some Sorbus (whitebeams). In pinnately coarse leaves the axial attitude in accepted as the midrib.

Characteristics of the petiole

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

Petiolated leaves accept a petiole (leaf stem). Sessile leaves do not: the brand attaches anon to the stem. In clasping or decurrent leaves, the brand partially or wholly surrounds the stem, generally giving the consequence that the shoot grows through the leaf. If this is in fact the case, the leaves are alleged "perfoliate", such as in Claytonia perfoliata. In peltate leaves, the brand attaches to the brand axial from the brand margin.

In some Acacia species, such as the Koa Timberline (Acacia koa), the petioles are broadcast or broadened and action like brand blades; these are alleged phyllodes. There may or may not be accustomed pinnate leaves at the tip of the phyllode.

A stipule, present on the leaves of abounding dicotyledons, is an addendum on anniversary ancillary at the abject of the brand akin a baby leaf. Stipules may be abiding and not be allow (a agree leaf, such as in roses and beans), or be allow as the brand expands, abrogation a blade blister on the accept (an exstipulate leaf).

• The situation, arrangement, and analysis of the stipules is alleged the "stipulation".
  • free
  • adnate : alloyed to the brand base
  • ochreate : provided with ochrea, or sheath-formed stipules, e.g. rhubarb,
  • encircling the brand base
  • interpetiolar : amid the petioles of two adverse leaves.
  • intrapetiolar : amid the brand and the subtending stem

Venation

Branching veins on abject of taro leaf

The venation aural the blade of a Lime tree.

The lower covering of Tilia x europea

Palmate-veined leaf

There are two subtypes of venation, namely, craspedodromous, breadth the above veins amplitude up to the allowance of the leaf, and camptodromous, if above veins extend abutting to the margin, but angle afore they bisect with the margin.

• Feather-veined, associate — the veins arise pinnately from a individual mid-vein and bisect into veinlets. These, in turn, anatomy a complicated network. This blazon of venation is archetypal for (but by no agency bound to) dicotyledons.
  • Pinnate-netted, penniribbed, penninerved, penniveined; the brand has usually one capital attitude (called the mid-vein), with veinlets, abate veins aberration off laterally, usually somewhat alongside to anniversary other; e.g. Malus (apples).
  • Three capital veins annex at the abject of the cell and run about alongside subsequently, as in Ceanothus. A agnate adjustment (with 3-7 veins) is abnormally apparent in Melastomataceae.
  • Palmate-netted, palmate-veined, fan-veined; several capital veins diverge from abreast the brand abject breadth the brand attaches, and afford adjoin the bend of the leaf; e.g. a lot of Acer (maples).
• Parallel-veined, parallel-ribbed, parallel-nerved, penniparallel — veins run parallel for the breadth of the leaf, from the abject to the apex. Commissural veins (small veins) affix the above alongside veins. Archetypal for a lot of monocotyledons, such as grasses.
• Dichotomous — There are no ascendant bundles, with the veins bifurcation consistently by pairs; begin in Ginkgo and some pteridophytes.

Note that although it is the added circuitous pattern, aberration veins arise to be plesiomorphic and in some anatomy were present in age-old seed plants as continued as 250 actor years ago. A pseudo-reticulate venation that is in fact a awful acclimatized penniparallel one is an autapomorphy of some Melanthiaceae which are monocots, e.g. Paris quadrifolia (True-lover's Knot).

Morphology changes aural a individual plant

• Homoblasty - Acclimatized in which a bulb has baby changes in brand size, shape, and advance addiction amid adolescent and developed stages.
• Heteroblasty - Acclimatized in which a bulb has apparent changes in brand size, shape, and advance addiction amid adolescent and developed stages.

Terminology

Chart illustrating some brand analysis terms

A allocation of a celery leaf

Shape

Edge

• ciliate: belted with hairs
• crenate: wavy-toothed; dentate with angled teeth, such as Fagus (beech)
• crenulate cautiously or shallowly crenate
• dentate: toothed, such as Castanea (chestnut)
  • coarse-toothed: with ample teeth
  • glandular toothed: with teeth that buck glands.
• denticulate: cautiously toothed
• doubly toothed: anniversary tooth address abate teeth, such as Ulmus (elm)
• entire: even; with a bland margin; after toothing
• lobate: indented, with the indentations not extensive to the center, such as abounding Quercus (oaks)
  • palmately lobed: biconcave with the indentations extensive to the center, such as Humulus (hop).
• serrate: denticulate with absurd teeth pointing forward, such as Urtica (nettle)
• serrulate: cautiously serrate
• sinuate: with deep, wave-like indentations; coarsely crenate, such as abounding Rumex (docks)
• spiny: with stiff, aciculate points, such as some Ilex (hollies) and Cirsium (thistles).

Tip

Leaves assuming assorted morphologies. Clockwise from high left: tripartite lobation, egg-shaped with denticulate margin, peltate with palmate venation, acicular odd-pinnate (center), pinnatisect, lobed, egg-shaped with absolute margin

• acuminate: long-pointed, abiding into a narrow, cone-shaped point in a biconcave manner.
• acute: catastrophe in a sharp, but not abiding point
• cuspidate: with a sharp, elongated, adamant tip; angled with a cusp.
• emarginate: indented, with a bank cleft at the tip.
• mucronate: abruptly angled with a baby abbreviate point, as a assiduity of the midrib; angled with a mucro.
• mucronulate: mucronate, but with a abate spine.
• obcordate: inversely heart-shaped, acutely alveolate at the top.
• obtuse: angled or blunt
• truncate: catastrophe abruptly with a collapsed end, that looks cut off.

Base

• acuminate: advancing to a sharp, narrow, abiding point.
• acute: advancing to a sharp, but not abiding point.
• auriculate: ear-shaped.
• cordate: heart-shaped with the cleft appear the stalk.
• cuneate: wedge-shaped.
• hastate: shaped like an halberd and with the basal lobes pointing outward.
• oblique: slanting.
• reniform: kidney-shaped but bastard and broader than long.
• rounded: arched shape.
• sagittate: shaped like an arrowhead and with the astute basal lobes pointing downward.
• truncate: catastrophe abruptly with a collapsed end, that looks cut off.

Surface

Scale-shaped leaves of a Norfolk Island Pine, Araucaria heterophylla.

• farinose: address farina; mealy, covered with a waxy, blanched powder.
• glabrous: smooth, not hairy.
• glaucous: with a blanched bloom; covered with a actual fine, bluish-white powder.
• glutinous: sticky, viscid.
• papillate, or papillose: address papillae (minute, nipple-shaped protuberances).
• pubescent: covered with arrect hairs (especially bendable and abbreviate ones).
• punctate: apparent with dots; dotted with depressions or with clear-cut glands or atramentous dots.
• rugose: acutely wrinkled; with veins acutely visible.
• scurfy: covered with tiny, ample scalelike particles.
• tuberculate: covered with tubercles; covered with warty prominences.
• verrucose: warted, with warty outgrowths.
• viscid, or viscous: covered with thick, adhesive secretions.

The brand apparent is aswell host to a ample array of microorganisms; in this ambience it is referred to as the phyllosphere.

The alongside veins aural an iris leaf.

Hairiness

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

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

"Hairs" on plants are appropriately alleged trichomes. Leaves can actualization several degrees of hairiness. The acceptation of several of the afterward agreement can overlap.

• arachnoid, or arachnose: with abounding fine, circuitous hairs giving a chiffon appearance.
• barbellate: with cautiously acid hairs (barbellae).
• bearded: with long, annealed hairs.
• bristly: with annealed hair-like prickles.
• canescent: age-old with abutting grayish-white pubescence.
• ciliate: hardly belted with abbreviate hairs (cilia).
• ciliolate: carefully ciliate.
• floccose: with flocks of soft, bristling hairs, which tend to rub off.
• glabrous: no hairs of any affectionate present.
• glandular: with a gland at the tip of the hair.
• hirsute: with rather asperous or annealed hairs.
• hispid: with rigid, barbate hairs.
• hispidulous: carefully hispid.
• hoary: with a fine, abutting grayish-white pubescence.
• lanate, or lanose: with bristling hairs.
• pilose: with soft, acutely afar hairs.
• puberulent, or puberulous: with fine, minute hairs.
• pubescent: with soft, abbreviate and arrect hairs.
• scabrous, or scabrid: asperous to the touch.
• sericeous: cottony actualization through fine, beeline and appressed (lying abutting and flat) hairs.
• silky: with adpressed, bendable and beeline pubescence.
• stellate, or stelliform: with star-shaped hairs.
• strigose: with appressed, sharp, beeline and annealed hairs.
• tomentose: densely boyish with matted, bendable white bristling hairs.
  • cano-tomentose: amid canescent and tomentose.
  • felted-tomentose: bristling and disordered with coiled hairs.
• villous: with continued and bendable hairs, usually curved.
• woolly:' with long, bendable and anfractuous or disordered hairs.

Adaptations

The lists in this commodity may accommodate items that are not notable, encyclopedic, or helpful. Please help out by removing such elements and accumulation acclimatized items into the capital physique of the article. (February 2008)

Poinsettia bracts are leaves which accept acquired red blush in adjustment to allure insects and birds to the axial flowers, an adaptive action commonly served by petals (which are themselves leaves awful acclimatized by evolution).

In the advance of evolution, leaves accept acclimatized to altered environments in the afterward ways:

• A assertive apparent analysis avoids moistening by rain and contagion (See Lotus effect).
• Sliced leaves abate wind resistance.
• Hairs on the brand apparent allurement clamminess in dry climates and actualize a ample boundary layer thereby abbreviation baptize loss.
• Waxy brand surfaces abate baptize loss.
• Large apparent breadth of brand provides ample breadth for sunlight and provides adumbration for bulb to abbreviate heating and abate baptize loss.
• In added or beneath blurred or active in the clay leaves, clear-cut windows clarify the ablaze afore the photosynthesis takes abode at the abutting brand surfaces (e.g. Fenestraria).
• Succulent leaves abundance baptize and amoebic acids for use in CAM photosynthesis.
• Aromatic oils, poisons or pheromones produced by brand borne glands avert herbivores (e.g. eucalypts).
• Inclusions of apparent minerals avert herbivores (e.g. silica in grasses.
• A transformation into petals attracts pollinators.
• A transformation into spines protects the plants (e.g. cacti).
• A transformation into insect accessories helps agriculture the plants (carnivorous plants).
• A transformation into bulbs helps autumn aliment and baptize (e.g. onions).
• A transformation into tendrils allows the bulb to ascend (e.g. peas).
• A transformation into bracts and pseudanthia (false flowers) replaces accustomed annual structures if the accurate flowers are acutely bargain (e.g. Spurges).

Interactions with added organisms

Some insects actor leaves (Kallima inachus shown)

A babe arena with leaves

Although not as alimental as added organs such as fruit, leaves accommodate a aliment antecedent for abounding organisms. Animals which eat leaves are accepted as folivores. The brand is one of the a lot of basic locations of the plant, and plants accept acquired aegis adjoin folivores such as tannins, chemicals which arrest the assimilation of proteins and accept an abhorrent taste.

Some animals accept cryptic adaptations to abstain their own predators. For example, some caterpillars will actualize a baby home in the brand by folding it over themselves, while added herbivores and their casualty mimic the actualization of the leaf. Some insects, such as the katydid, crop this even further, affective from ancillary to ancillary abundant like a brand does in the wind.

Bibliography

• Leaves: The formation, charactistics and uses of hundred of leaves in all locations of the world by Ghillean Tolmie Prance. 324 accurate plates in atramentous and white, and colour by Kjell B Sandved 256 pages²

Footnotes

See also

• Abscission (losing of leaves)
• Cladophyll
• Guttation (beads of aqueous basic at brand margins)
• Leaf breadth index
• Phylloclade
• Vernation (sprouting of leaves)
• Evolution of leaves
• Leaf protein concentrate

External links

Wikimedia Commons has media accompanying to: Leaves

Look up leaf in Wiktionary, the chargeless dictionary.

• VASCULAR PLANT SYSTEMATICS Breadth B. General Characters and Character States: Position and Arrangement
• Science aid: Leaf Brand analysis and change ability for teens.

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