Forum Thread

Japan is an island by the sea filled with volcanoes and it's ♪♫ beautiful ♫♪.

In the year negative a billion, Japan might not have been here. In the year negative forty thousand, it was here, and you could walk to it, and some people walked to it. Then it got warmer, some icebergs melted, it became an island, and now there's lots of ♫ trees ♫. Because it's warmer.

So now there's people on the island; they're basically sort of hanging out in between the mountains eating nuts off trees and using the latest technology. Like stones, and bowls.

Ding dong, it's the outside world, and they have technology from the future. Like really good metal, and ♪ crazy rice farms ♪. Now you can make a lot of rice really really quickly. That means if you own the farm, then you own a lot of food, which is something everybody needs to survvvvive. So that makes you king.

Rice farming and rice kingdoms spread all across the land, all the way to here. The most important kingdoms were here (Hi), here (Chikushi), here (Izumo), here (Kibi), here (Yamato), here (Koshi), and here (Kenu). But this one (Yamato) was the most most important, ruled by a heavenly superperson, or emperor for short.

Knock knock, get the door, it's religion. The new prince wants everyone to try this hot new religion (Buddhism) from Baekje.
"Please try this religion," he said.
"No," said everybody.
"Try iiiiit," he said.
"no," said everybody again, quieter this time.
And so the religion was put into place and all the rules that came with it.

Then, the government was taken over by another clique (Taika). And they made some reforms , like making the government govern more, and making the government more like China's government, which is a government that governs more.
"Hi China," they said.
"Hi dip (wa, dwarf)," said China.
"Can you call us something else, other than dip?" said Japan.
"Like what?" said China.
♫♪"How about sunrise laaand?"♪♫ said Japan.
And they stole China's alphabet and wrote a book. About themselves! And then they made lots of poetry and art and another book about themselves.

Then they stopped moving the capital every time the emperor died and kept it in one place for a while, right here (Kyoto, Heian Palace). And they conquered the north finally, get that squared away.

A rich hipster named Kūkai is bored with modern Buddhism and visits China, learns a better version which is more ♫♪ spiritual ♪♫, comes back, reinvents the alphabet, and causes art and literature to be ♫♪ great ♪♫ for a long time. And the royal palace turned into such a dreamworld of art that they really didn't give a about running the country.

So if you live outside the palace, how are you supposed to protect your , from criminals? ♫♪ Hire a samurai. ♪♫ Everyone started hiring samurai. Rich important people hired samurai. Poor people who could not afford to hire samurai did not hire samurai. The samurai became organized and powerful, more powerful than the government. So they made their own military government, right here. They let the emperor still be emperor, but the shogun was actually in control.

Breaking news, the Mongols have invaded China.
"W̛e҉'ve i͟nv̕aded ̵Chi͠na̸," said the Mongols, "Pl͘e̶a̷se̵ ͝res͢p̛ȩc̷t u͢s҉,͜ or͜ el̕se w͞e ͟m̛igh͟t ͠i͝nvade͡ ̕y͜o̕u̕ ͡a͡s̕ ̡well̀.̢"
"Okay," said Japan.
So the Mongols came over, ready for war, and died in a tornadotyphoon. But they tried again, and had a nice time fighting with the Japanese, but then died in a tornadotyphoon.

Then the emperor overthrows the shogunate, then the shogunate overthrows him back and moves to Kyoto, and makes a new shogunate. And the emperor can still dress like an emperor if he wants, that's fine.

♫♪ Now there's more art. ♪♫
Like painting with less colors, collaborative poetry, plays, monkey fun, tea parties, gardening, architecture, flowers.

It's time for who's going to be the next shogun. Usually it's the shogun's kid, but the shogun doesn't have a kid. So he tries to get his brother to quit being a monk and be the next shogun. He says okay. But then the shogun has a kid. So now who's it gonna be? Vote now on your phones. And everyone voted so hard that the palace caught on fire and burned down. The shogun actually didn't care, he was off somewhere doing poetry. And the whole country broke into pieces. Everyone is fighting with each other for local power, and it's anybody's game.

Knock knock, it's Europe. No, they're not here to take over, they just wanna sell some . Like clocks, and guns, and ♫♪ Jesus ♪♫. So that's cool. But everyone's still fighting each other for control. Now with guns! And wouldn't it be nice to control the capital, which right now is puppets, with no one controlling them? This clan (Imagawa) is ready to make a run for it, but first they have to trample this smaller clan (Oda) which is in the way. Surprise, smaller clan wins! And the leader of that clan (Oda Nobunaga) steals the idea of invading the capital, and invades the capital. And it goes very well.

He's about halfway through conquering Japan when someone who works for him kills him, then someone else who works for him (Toyotomi Hideyoshi) kills them, and that guy finishes conquering Japan. And then he confiscated everybody's swords. And he made some rules.
"Ąnd͟ n͟ow I'̛m̶ goińg̡ to ͘inva͞d̨e ͝Kor͟e͡a,̵ an͝d͢ ̶the̴n h͜op̷ef̕ull͏y ̵Chin͢a̛," he said, and failed, and also died.
But before he died, he told these five guys to take care of his five year old son until he's old enough to be the next ruler of Japan. And the five guys said yeah right, it's not gonna be this kid, it's gonna be one of us. 'Cause we're grownups. And it's probably gonna be this guy (Tokugawa Ieyasu) who happens to be way more rich and powerful than the others.

A lot of people support him, but a lot of people (Ishida Mitsunari) support not supporting him. They have a fight, and he wins. And starts a new government, right here. ♫♪ Edo ♫♪ And he still lets the emperor dress like an emperor, and have very nice things. But don't get confused, this (Tokugawa family) is the new government. And they are very strict, so strict they close the country. No one can leave, and no one can come in. Except for the Dutch, if they wanna buy and sell , but they have to do it right here (Dejima).

Now that the entire country was not at war with itself, the population increased a lot. Business increased, schools were built, roads were built, everyone learned to read, books were published. There was poetry (haiku), plays (kabuki), sexytimes, puppet shows (bunraku), and Dutch studies. People started to study European science from books they bought from the Dutch. We're talking geography, skeletons, physics, chemistry, astronomy, and maybe even electricity.

Over time, the economic and cultural prosperity began to gradually slow do-
*impending doom music*
Knock knock. It's the United States. With huge boats. With guns. Gunboats.
"O͜pe͡ņ,̨ t͡he͏ ͘c̷o̷ưntry. ͠S̛t͜o̡p̛,̵ ҉ha͠v̀in͜g̷ i͝t̀ ͝be̴ ́clo͞sed.̢" said the United States.
*music ends*
There was really nothing they could do, so they signed a contract that lets United States, Britain, and Russia visit Japan anytime they want.

Chōshu and Satsuma hated this. "That sucks!" they said. "This sucks!!!"
And with almost very little outside help, (from Britain) they overthrew the shogunate. And somehow made the emperor the emperor again, and moved him to Edo, which they renamed eastern capital (Tokyo). They made a new government, which was a lot more Western. And they made a new constitution, which was.. pretty Western. And a military that was... pretty Western (large).

And do you know what else is Western? That's right, it's conquering stuff. So what can we conquer? Korea! They conquer Korea, taking it from its previous owner, China, and then go a little bit further (Liaodong Peninsula).
And Russia rushes in out of nowhere and says, "Stop no you can't do that we were gonna build a railroad through here to try to get some warm water." And Russia builds their railroad, supervised by atton of soldiers. Then, when the railroad was done, they downgraded to a fuckton. Did I say downgrade? I meant upgrade.
And Japan says, "Can you maybe chill?"
And Russia says, "How 'bout maybe you chill?"

Japan is kind of scared of Russia. You'll never guess who's also kind of scared of Russia. Great Britain! So Japan and Great Britain make an alliance together so they can be a little less scared of Russia. Feeling confident, Japan goes to war against Russia, but just for a moment, and then they both get tired and stop.

♫♪ It's time for World War I ♪♫
The world is about to have a war. Because it's the 1900s, and weapons are getting crazy, and all these empires are excited to try them out on each other. Meanwhile, Japan has been enjoying conquering stuff and wants m̵͡͝͝o͏̨̨̢͢o͏͏̵̧̕ơ̢̢͜͜o͠͏͢ó͘o̶̢̧ó̷͝͠o͝͡o̧͘r̨̢̕ȩ̸ and the next thing on their list is this part of China (Qingdao) and lots of tiny islands.

All that stuff belongs to Germany, which just had war declared on by Britain, because Britain was friends with Belgium, who was being trespassed by Germany in order to get to France to kick France's ass because France was friends with Russia who was getting ready to kick Austria's ass because Austria was getting ready to kick Serbia's ass because someone from Serbia shot the leader of Austria's ass. Err, actually, he shot him in the head. And Britain is currently friends with Japan. So you know what that means, duhhh.

♫♪ Japan should take the islands. ♪♫ Which they wanted to do anyway. So they sort of called Britain on the tele(gram) to sort of let them know, and then they did it! And they also helped Britain here and there with some errands and stuff. *bell rings*

Now the war is over, and congratulations Japan, you technically fought in the war which means you get to sit at the negotiating table (Paris Peace Conference), with the big dudes, where they decided who owns what. And yes, Japan gets to keep all that they stole from Germany. And you also get to join the post-war mega alliance ♫♪ the League of Nations ♪♫ whose mission statement is to try not to take over the world.

The Great Depression is bad, and Japan's economy is now crappy. But the military is doing just fine, and it invades Manchuria. And the League of Nations is like ♪"No don't do that if you're in the League of Nations you're not supposed to try to take over the world."♪
And Japan said, ♫♪ How bout I do, anyway? ♪♫ And Japan invaded more and more and more of China, and was planning to invade the entire East.

You've got mail.
It's from Germany, the new leader of Germany, he has a cool mustache and is trying to take over the world and needs friends. This also got forwarded to Italy. They all decided to be friends because they had so much in common.

♫♪ It's time for World War II ♪♫
Germany is invading the neighbors, then they invade the neighbors' neighbors, then, the neighbor's neighbors' neighbors, who happen to be Britain, said "Holy shiiit" and the United States started helping Britain because they are ♫♪ good friends ♪♫ and started not helping Japan because ♫♪" Their friends and our friends are not friends. Plus they're planning on invaaading the entire ocean."♪♫

The United States is also working on a large, very huge bomb. Bigger than any other bomb, ever. Just in case (Germany). But they still haven't joined the war, war looks bad on TV, and the United States is really starting to care about their image.

But then Japan spits on them, in Hawai'i, and challenges them to war. And they say yes! And then Germany, as a symbol of friendship, declares war on the United States also. And they help the gang chase Germany back into Germany. And they also chase Japan back into Japan. And they haven't used the bomb yet, and are curious to see if it works, so they drop it on Japan.


They actually drop two.













(You win.)
The United States installed a new government, inspired by the United States government, with just the right ingredients for a ♫♪ post-war economic miracle ♪♫ and Japan starts making TVs, VCRs, automobiles, and camcorders as fast as they can. And also better than everybody else. They get rich, and the economy goes wild. But then the miracle wears off, but everything's still pretty cool I guess. ♪♫ Bye. ♫♪

Leaf

For other uses, see Leaf (disambiguation).

A leaf is an organ of a vascular plant and is the principal lateral appendage of the stem. The leaves and stem together form the shoot. Foliage is a mass noun that refers to leaves collectively.

Typically a leaf is a thin, dorsiventrally flattened organ, borne above ground and specialized for photosynthesis. In most leaves, the primary photosynthetic tissue, the (palisade mesophyll), is located on the upper side of the blade or lamina of the leaf but in some species, including the mature foliage of Eucalyptus palisade mesophyll is present on both sides and the leaves are said to be isobilateral. Most leaves have distinctive upper (adaxial) and lower (abaxial) surfaces that differ in colour, hairiness, the number of stomata (pores that intake and output gases), epicuticular wax amount and structure and other features.

Broad, flat leaves with complex venation are known as megaphylls and the species that bear them, the majority, as broad-leaved or megaphyllous plants. In others, such as the clubmosses, with different evolutionary origins, the leaves are simple, with only a single vein and are known as microphylls.

Some leaves, such as bulb scales are not above ground, and in many aquatic species the leaves are submerged in water. Succulent plants often have thick juicy leaves, but some leaves are without major photosynthetic function and may be dead at maturity, as in some cataphylls, and spines). Furthermore, several kinds of leaf-like structures found in vascular plants are not totally homologous with them. Examples include flattened plant stems called phylloclades and cladodes, and flattened leaf stems called phyllodes which differ from leaves both in their structure and origin. Many structures of non-vascular plants, such as the phyllids of mosses and liverworts and even of some foliose lichens, which are not plants at all (in the sense of being members of the kingdom Plantae), look and function much like leaves.
General characteristicsEdit

Typically leaves are broad, flat and thin (dorsiventrally flattened), at least in their early development, thereby maximising the surface area directly exposed to light and enabling the light to penetrate the tissues and reach the chloroplasts, thus promoting photosynthesis. They are arranged on the plant so as to expose their surfaces to light as efficiently as possible without shading each other, but there are many exceptions and complications. For instance plants adapted to windy conditions may have pendent leaves, such as in many willows and eucalypts. Also conifers, whose leaves are needle shaped. The flat, or laminar, shape also maximises thermal contact with the surrounding air. The leaf shape also minimises damage from wind, by creating turbulence rather than resistance.[citation needed] Functionally, in addition to photosynthesis the leaf is the principal site of transpiration and guttation. Leaves also function to store chemical energy and water (especially succulents) and may become specialised organs serving other functions.[which?]

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. Their surfaces are waterproofed by the plant cuticle and gas exchange between the mesophyll cells and the atmosphere is controlled by minute openings called stomata, about 10 μm which open or close to regulate the rate exchange of carbon dioxide, oxygen, and water vapour into and out of the internal intercellular space system. Stomatal opening is controlled by the turgor pressure in a pair of guard cells that surround the stomatal aperture. In any square centimeter of a plant leaf there may be from 1,000 to 100,000 stomata.

Many gymnosperms have thin needle-like or scale-like leaves that can be advantageous in cold climates with frequent snow and frost. These are interpreted as reduced from megaphyllous leaves of their Devonian ancestors. 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 herbivory. For xerophytes the major constraint is not light flux or intensity, but drought. Some window plants such as Fenestraria species and some Haworthia species such as Haworthia tesselata and Haworthia truncata are examples of xerophytes. and Bulbine mesembryanthemoides.

The shape and structure of leaves vary considerably from species to species of plant, depending largely on their adaptation to climate and available light, but also to other factors such as grazing animals (such as deer), available nutrients, and ecological competition from other plants. Considerable changes in leaf type occur within species too, for example as a plant matures; as a case in point Eucalyptus species commonly have isobilateral, pendent leaves when mature and dominating their neighbours; however, such trees tend to have erect or horizontal dorsiventral leaves as seedlings, when their growth is limited by the available light. Other factors include the need to balance water loss at high temperature and low humidity against the need to absorb atmospheric carbon dioxide. In most plants leaves also are the primary organs responsible for transpiration and guttation (beads of fluid forming at leaf margins).

Leaves can also store food and water, and are modified accordingly to meet these functions, for example in the leaves of succulent plants and in bulb scales. The concentration of photosynthetic structures in leaves requires that they be richer in protein, minerals, and sugars than, say, woody stem tissues. Accordingly, leaves are prominent in the diet of many animals.


A leaf shed in autumn.
Correspondingly, leaves represent heavy investment on the part of the plants bearing them, and their retention or disposition are the subject of elaborate strategies for dealing with pest pressures, seasonal conditions, and protective measures such as the growth of thorns and the production of phytoliths, lignins, tannins and poisons.

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.

The leaf-like organs of Bryophytes (e.g., mosses and liverworts), known as phyllids, differ morphologically from the leaves of vascular plants in that they lack vascular tissue, are usually only a single cell thick and have no cuticle stomata or internal system of intercellular spaces.

Simple, vascularised leaves (microphylls) first evolved as enations, extensions of the stem, in clubmosses such as Baragwanathia during the Silurian period. True leaves or euphylls of larger size and with more complex venation did not become widespread in other groups until the Devonian period, by which time the carbon dioxide concentration in the atmosphere had dropped significantly. This occurred independently in several separate lineages of vascular plants, in progymnosperms like Archaeopteris, in Sphenopsida, ferns and later in the gymnosperms and angiosperms. Euphylls are also referred to as macrophylls or megaphylls (large leaves).

Morphology (large-scale features)Edit

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. The upper (adaxial) angle between a leaf and a stem is known as the axil of the leaf. It is often the location of a bud. Structures located there are called "axillary".

External leaf characteristics, such as shape, margin, hairs, the petiole, and the presence of stipules, are important for identifying plant species, and botanists have developed a rich terminology for describing leaf characteristics. Leaves have determinate growth. They grow to a specific pattern and shape and then stop. Other plant parts like stems or roots have non-determinate growth, and will usually continue to grow as long as they have the resources to do so.

The type of leaf is usually characteristic of a species (monomorphic), although some species produce more than one type of leaf (dimorphic or polymorphic). The longest leaves are those of the Raffia palm, R. regalis which may be up to 25 m (82.38 ft) long and 3 m (9.84 ft) wide. The terminology associated with the description of leaf morphology is presented, in illustrated form, at Wikibooks.

Where leaves are basal, and lie on the ground, they are referred to as prostrate.

Basic leaf typesEdit


Ferns have fronds
Conifer leaves are typically needle- or awl-shaped or scale-like
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 and many other monocots)
Other specialized leaves (such as those of Nepenthes, a pitcher plant)
Arrangement on the stemEdit

Main article: Phyllotaxis
Different terms are usually used to describe the arrangement of leaves on the stem (phyllotaxis):

Alternate – leaf attachments are singular at nodes, and leaves alternate direction, to a greater or lesser degree, along the stem.
Basal – arising from the base of the stem.
Cauline – arising from the aerial 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 and decussate if, as typical, each successive pair is rotated 90° progressing along the stem.
Whorled (Verticillate) – 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. Pseudoverticillate describes an arrangement only appearing whorled, but not actually so.
Rosulate – leaves form a rosette
Rows – The term "distichous" literally means "two rows". Leaves in this arrangement may be alternate or opposite in their attachment. The term "2-ranked" is equivalent. The terms tristichous and tetrastichous are sometimes encountered. For example, the "leaves" (actually microphylls) of most species of Selaginella are tetrastichous, but not decussate.
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° × 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 and the denominator indicates the number of leaves in the arrangement. This can be demonstrated by the following:

alternate leaves have an angle of 180° (or 1/2)
120° (or 1/3) : 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 bladeEdit


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 being 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 of 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 group of pinnules on each secondary vein forms a "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 petioleEdit

Petiolated leaves have a petiole (leaf stem), and are said to be petiolate.

Sessile (epetiolate) leaves have no petiole and the blade attaches directly to the stem. Subpetiolate leaves are nearly petiolate or have an extremely short petiole and may appear to be sessile.

In clasping or decurrent leaves, the blade partially surrounds the stem.

When the leaf base completely surrounds the stem, the leaves are said to be perfoliate, such as in Claytonia perfoliata.

In peltate leaves, the petiole attaches to the blade inside 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, lateral, as in Hibiscus.
adnate : fused to the petiole base, as in Rosa.
ochreate : provided with ochrea, or sheath-formed stipules, as in Polygonaceae, e.g. rhubarb.
encircling the petiole base
interpetiolar : between the petioles of two opposite leaves, as in Rubiaceae.
intrapetiolar : between the petiole and the subtending stem, as in Malpighiaceae.
VenationEdit

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.
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 plantEdit

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.
General characteristicsEdit

Typically leaves are broad, flat and thin (dorsiventrally flattened), at least in their early development, thereby maximising the surface area directly exposed to light and enabling the light to penetrate the tissues and reach the chloroplasts, thus promoting photosynthesis. They are arranged on the plant so as to expose their surfaces to light as efficiently as possible without shading each other, but there are many exceptions and complications. For instance plants adapted to windy conditions may have pendent leaves, such as in many willows and eucalypts. Also conifers, whose leaves are needle shaped. The flat, or laminar, shape also maximises thermal contact with the surrounding air. The leaf shape also minimises damage from wind, by creating turbulence rather than resistance.[citation needed] Functionally, in addition to photosynthesis the leaf is the principal site of transpiration and guttation. Leaves also function to store chemical energy and water (especially succulents) and may become specialised organs serving other functions.[which?]

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. Their surfaces are waterproofed by the plant cuticle and gas exchange between the mesophyll cells and the atmosphere is controlled by minute openings called stomata, about 10 μm which open or close to regulate the rate exchange of carbon dioxide, oxygen, and water vapour into and out of the internal intercellular space system. Stomatal opening is controlled by the turgor pressure in a pair of guard cells that surround the stomatal aperture. In any square centimeter of a plant leaf there may be from 1,000 to 100,000 stomata.

Many gymnosperms have thin needle-like or scale-like leaves that can be advantageous in cold climates with frequent snow and frost. These are interpreted as reduced from megaphyllous leaves of their Devonian ancestors. 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 herbivory. For xerophytes the major constraint is not light flux or intensity, but drought. Some window plants such as Fenestraria species and some Haworthia species such as Haworthia tesselata and Haworthia truncata are examples of xerophytes. and Bulbine mesembryanthemoides.

The shape and structure of leaves vary considerably from species to species of plant, depending largely on their adaptation to climate and available light, but also to other factors such as grazing animals (such as deer), available nutrients, and ecological competition from other plants. Considerable changes in leaf type occur within species too, for example as a plant matures; as a case in point Eucalyptus species commonly have isobilateral, pendent leaves when mature and dominating their neighbours; however, such trees tend to have erect or horizontal dorsiventral leaves as seedlings, when their growth is limited by the available light. Other factors include the need to balance water loss at high temperature and low humidity against the need to absorb atmospheric carbon dioxide. In most plants leaves also are the primary organs responsible for transpiration and guttation (beads of fluid forming at leaf margins).

Leaves can also store food and water, and are modified accordingly to meet these functions, for example in the leaves of succulent plants and in bulb scales. The concentration of photosynthetic structures in leaves requires that they be richer in protein, minerals, and sugars than, say, woody stem tissues. Accordingly, leaves are prominent in the diet of many animals.


A leaf shed in autumn.
Correspondingly, leaves represent heavy investment on the part of the plants bearing them, and their retention or disposition are the subject of elaborate strategies for dealing with pest pressures, seasonal conditions, and protective measures such as the growth of thorns and the production of phytoliths, lignins, tannins and poisons.

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.

The leaf-like organs of Bryophytes (e.g., mosses and liverworts), known as phyllids, differ morphologically from the leaves of vascular plants in that they lack vascular tissue, are usually only a single cell thick and have no cuticle stomata or internal system of intercellular spaces.

Simple, vascularised leaves (microphylls) first evolved as enations, extensions of the stem, in clubmosses such as Baragwanathia during the Silurian period. True leaves or euphylls of larger size and with more complex venation did not become widespread in other groups until the Devonian period, by which time the carbon dioxide concentration in the atmosphere had dropped significantly. This occurred independently in several separate lineages of vascular plants, in progymnosperms like Archaeopteris, in Sphenopsida, ferns and later in the gymnosperms and angiosperms. Euphylls are also referred to as macrophylls or megaphylls (large leaves).

Morphology (large-scale features)Edit

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. The upper (adaxial) angle between a leaf and a stem is known as the axil of the leaf. It is often the location of a bud. Structures located there are called "axillary".

External leaf characteristics, such as shape, margin, hairs, the petiole, and the presence of stipules, are important for identifying plant species, and botanists have developed a rich terminology for describing leaf characteristics. Leaves have determinate growth. They grow to a specific pattern and shape and then stop. Other plant parts like stems or roots have non-determinate growth, and will usually continue to grow as long as they have the resources to do so.

The type of leaf is usually characteristic of a species (monomorphic), although some species produce more than one type of leaf (dimorphic or polymorphic). The longest leaves are those of the Raffia palm, R. regalis which may be up to 25 m (82.38 ft) long and 3 m (9.84 ft) wide. The terminology associated with the description of leaf morphology is presented, in illustrated form, at Wikibooks.

Where leaves are basal, and lie on the ground, they are referred to as prostrate.

Basic leaf typesEdit


Ferns have fronds
Conifer leaves are typically needle- or awl-shaped or scale-like
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 and many other monocots)
Other specialized leaves (such as those of Nepenthes, a pitcher plant)
Arrangement on the stemEdit

Main article: Phyllotaxis
Different terms are usually used to describe the arrangement of leaves on the stem (phyllotaxis):

Alternate – leaf attachments are singular at nodes, and leaves alternate direction, to a greater or lesser degree, along the stem.
Basal – arising from the base of the stem.
Cauline – arising from the aerial 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 and decussate if, as typical, each successive pair is rotated 90° progressing along the stem.
Whorled (Verticillate) – 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. Pseudoverticillate describes an arrangement only appearing whorled, but not actually so.
Rosulate – leaves form a rosette
Rows – The term "distichous" literally means "two rows". Leaves in this arrangement may be alternate or opposite in their attachment. The term "2-ranked" is equivalent. The terms tristichous and tetrastichous are sometimes encountered. For example, the "leaves" (actually microphylls) of most species of Selaginella are tetrastichous, but not decussate.
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° × 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 and the denominator indicates the number of leaves in the arrangement. This can be demonstrated by the following:

alternate leaves have an angle of 180° (or 1/2)
120° (or 1/3) : 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 bladeEdit


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 being 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 of 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 group of pinnules on each secondary vein forms a "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 petioleEdit

Petiolated leaves have a petiole (leaf stem), and are said to be petiolate.

Sessile (epetiolate) leaves have no petiole and the blade attaches directly to the stem. Subpetiolate leaves are nearly petiolate or have an extremely short petiole and may appear to be sessile.

In clasping or decurrent leaves, the blade partially surrounds the stem.

When the leaf base completely surrounds the stem, the leaves are said to be perfoliate, such as in Claytonia perfoliata.

In peltate leaves, the petiole attaches to the blade inside 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, lateral, as in Hibiscus.
adnate : fused to the petiole base, as in Rosa.
ochreate : provided with ochrea, or sheath-formed stipules, as in Polygonaceae, e.g. rhubarb.
encircling the petiole base
interpetiolar : between the petioles of two opposite leaves, as in Rubiaceae.
intrapetiolar : between the petiole and the subtending stem, as in Malpighiaceae.
VenationEdit

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.
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 plantEdit

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.
TerminologyEdit


ShapeEdit

Main article: Leaf shape

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


ciliate: fringed with hairs
crenate: wavy-toothed; dentate with rounded teeth
crenulate: finely or shallowly crenate
dentate: toothed, such as Castanea (chestnut)
coarse-toothed or coarsely dentate: with large teeth
glandular toothed or glandularly dentate: 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
linear: parallel margins, elongated
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).
TipEdit


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 noticeably diminutive spine, a mucronule.
obcordate: inversely heart-shaped, deeply notched at the top.
obtuse: rounded or blunt
truncate: ending abruptly with a flat end, that looks cut off.

BaseEdit


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.
SurfaceEdit



coriaceous: leathery; stiff and tough, but somewhat flexible.
farinose: bearing farina; mealy, covered with a waxy, whitish powder.
glabrous: smooth, not hairy.
glaucous: with a whitish bloom; covered with a very fine, bluish-white powder.
glutinous: sticky, viscid.
lepidote coated with small scales (thus elepidote, without such scales).
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.


The parallel veins within an iris leaf
HairinessEdit




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.
TimingEdit

hysteranthous (hysteranthy): developing after the flowers
synanthous (synanthy): developing at the same time as the flowers
Surface patterningEdit

maculate: stained, spotted, compare immaculate.
Vein patterningEdit

channelled: sunken below the surface, resulting in a rounded channel
SizeEdit

Main article: Leaf size
The terms megaphyll, macrophyll, mesophyll, notophyll, microphyll, nanophyll and leptophyll are used to describe leaf sizes (in descending order), in a classification devised in 1934 by Christen C. Raunkiær and since modified by others.

Anatomy (medium and small scale)Edit

Medium-scale featuresEdit

Leaves are normally extensively vascularised and typically have networks of vascular bundles containing xylem, which supplies water for photosynthesis, and phloem, which transports the sugars produced by photosynthesis. Many leaves are covered in trichomes (small hairs) which have diverse structures and functions.

Medium scale diagram of leaf internal anatomy
Small-scale featuresEdit

The major tissue systems present are

The epidermis, which covers the upper and lower surfaces
The mesophyll tissue inside the leaf, which is rich in chloroplasts (also called chlorenchyma)
The arrangement of veins (the vascular tissue)
These three tissue systems typically form a regular organisation at the cellular scale. Specialised cells that differ markedly from surrounding cells, and which often synthesise specialised products such as crystals, are termed idioblasts.

Fine scale diagram of leaf structure
Major leaf tissuesEdit

EpidermisEdit


The epidermis is the outer layer of cells covering the leaf. It is covered with a waxy cuticle which is impermeable to liquid water and water vapor and forms the boundary separating the plant's inner cells from the external world. The cuticle is in some cases thinner on the lower epidermis than on the upper epidermis, and is generally thicker on leaves from dry climates as compared with those from wet climates.[citation needed] 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)[which?] 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 tissue includes several differentiated cell types; epidermal cells, epidermal hair cells (trichomes), cells in the stomatal complex; guard cells and subsidiary cells. The epidermal cells are the most numerous, largest, and least specialized and form the majority of the epidermis. These are typically more elongated in the leaves of monocots than in those of dicots.

Chloroplasts are generally absent in epidermal cells, the exception being the guard cells of the stomata. The stomatal pores perforate the epidermis and are surrounded on each side by chloroplast-containing guard cells, and two to four subsidiary cells that lack chloroplasts, forming a specialized cell group known as the stomatal complex. The opening and closing of the stomatal aperture is controlled by the stomatal complex and regulates the exchange of gases and water vapor between the outside air and the interior of the leaf. Stomata therefore play the 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 are more numerous in plants from cooler climates.

MesophyllEdit

For the term Mesophyll in the size classification of leaves, see Leaf size.
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 vertically elongated cells, one to two cells thick, directly beneath the adaxial epidermis, with intercellular air spaces between them. Its cells contain many more chloroplasts than the spongy layer. These long cylindrical cells are regularly arranged in one to five rows. Cylindrical cells, with the chloroplasts close to the walls of the cell, can take optimal advantage of light. The slight separation of the cells provides maximum absorption of carbon dioxide. This separation must be minimal to afford capillary action for water distribution.[citation needed] 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 branched and not so tightly packed, so that there are large intercellular air spaces between them for oxygen and carbon dioxide to diffuse in and out of during respiration and photosynthesis. These cells contain fewer chloroplasts than those of the palisade layer. The pores or stomata of the epidermis open into substomatal chambers, which are connected to the air spaces between the spongy layer cells.
Leaves are normally green, due to chlorophyll in chloroplasts in the chlorenchyma cells. Plants that lack chlorophyll cannot photosynthesize.

VeinsEdit


The veins of a bramble leaf
The veins are the vascular tissue of the leaf and are located in the spongy layer of the mesophyll. The pattern of the veins is called venation. In angiosperms the venation is typically parallel in monocotyledons and forms an interconnecting network in broad-leaved plants. They were once thought to be typical examples of pattern formation through ramification, but they may instead exemplify a pattern formed in a stress tensor field.

A vein is made up of a vascular bundle. At the core of each bundle are clusters of two distinct types of conducting cells:

Xylem: cells that bring water and minerals from the roots into the leaf.
Phloem: cells that usually move sap, with dissolved sucrose, produced by photosynthesis in the leaf, out of the leaf.
A sheath of ground tissue made of lignin surrounding the vascular tissue. This sheath has a mechanical role in strengthening the rigidity 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 sheath, which usually includes some structural collenchyma tissue.

Leaf developmentEdit

According to Agnes Arber's partial-shoot theory of the leaf, leaves are partial shoots, being derived from leaf primordia of the shoot apex. Compound leaves are closer to shoots than simple leaves. Developmental studies have shown that compound leaves, like shoots, may branch in three dimensions. On the basis of molecular genetics, Eckardt and Baum (2010)[citation needed] concluded that "it is now generally accepted that compound leaves express both leaf and shoot properties."

AdaptationsEdit

Seasonal leaf lossEdit


A girl playing with leaves
Leaves in temperate, boreal, and seasonally dry zones may be seasonally deciduous (falling off or dying for the inclement season). This mechanism to shed leaves is called abscission. When the leaf is shed, it leaves a leaf scar on the twig. In cold autumns, they sometimes change color, and turn yellow, bright-orange, or red, as various accessory pigments (carotenoids and xanthophylls) are revealed when the tree responds to cold and reduced sunlight by curtailing 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. Optical masking of chlorophyll by anthocyanins reduces risk of photo-oxidative damage to leaf cells as they senesce, which otherwise may lower the efficiency of nutrient retrieval from senescing autumn leaves.

Interactions with other organismsEdit


Although not as nutritious as other organs such as fruit, leaves provide a food source for many organisms. The leaf is a vital source of energy production for the plant, and plants have evolved protection against animals that consume leaves, such as tannins, chemicals which hinder the digestion of proteins and have an unpleasant taste. Animals that are specialized to eat leaves are known as folivores.

Some species have cryptic adaptations by which they use leaves in avoiding predators. For example, the caterpillars of some leaf-roller moths will create a small home in the leaf by folding it over themselves. Some sawflies similarly roll the leaves of their food plants into tubes. Females of the Attelabidae, so-called leaf-rolling weevils, lay their eggs into leaves that they then roll up as means of protection. Other herbivores and their predators mimic the appearance of the leaf. Reptiles such as some chameleons, and insects such as some katydids, also mimic the oscillating movements of leaves in the wind, moving from side to side or back and forth while evading a possible threat.