Foliage and Their Function --how Plants Live and Thrive.

Autumn colours

Green leaves give way to autumn colours
Green leaves give way to autumn colours | Source

Notes from a Lancashire Countryman.

This is the second article in the series looking at how plants and trees live and thrive. In the first article  it was the roots and rhizomes that was under review. As with the previous article i will endeavour to keep the text in simple terms in the hope that it will be of interest and not bogged down in technical jargon or complicated botanical terminology.


We all know what leaves are they are a familiar feature of our everyday lives. but what is the function of these organs to the flora to which they are attached.? Leaves are the main component by which a plant breathes and they harness the energy provided by the sunlight passing through the chlorophyll, which absorbs carbon dioxide and releases oxygen back into the air. Another important function of the leaf is giving off surplus moisture {transpiration] and the formation of food reserves.

To achieve the delicate chemical reaction of changing carbon dioxide into oxygen, is dependent on the amount of daylight available and the air temperature. Thus during the hours of darkness this reaction cannot occur.  The chlorophyll {responsible for the green colouring} is no longer required. Starches and other nutrients stored is returned via the veins to the parent plant, and the green turns to russets and gold before their eventual departure from their grip.

This alludes to the deciduous  leaves, those species of plants and trees that loose all their leaves for part of the year. The term for this process is abscission. { frrom Latin ab-meaning away+ sussio- a cleaving} The word deciduous derives from Latin deciduus meaning to fall from decidere -to fall down.


Some tree including young oak trees cling on to their brown withered leaves through the winter only discarding them when the new buds of spring force them off. These leaves are termed by botanists as being marcescent leaves from the Latin marcere meaning to wither.

Young Oak in Winter

YOUNG OAK HANGING ON TO ITS WITHERED LEAVES.
YOUNG OAK HANGING ON TO ITS WITHERED LEAVES. | Source

Most of the foliage of seed bearing plants and tree consist of a leaf stalk referred to as a petiole, a leaf blade referred to as the lamina and stipules which are small growths located at either side at the base of the petiole. Where the leaf stalk joins the stem or twig it forms a junction known as the leaf axil. Not all species produce foliage with petioles. 

The leaf consists of 3 main types of tissue. --

The epidermis from the Greek epi-meaning upon, above or over+ derma skin. The epidermis forms a protective outer covering on the upper and lower surfaces.

An interior chlorenchyme called mesophyll from the Greek- misos meaning middle_phyll indicating type.

An arrangement of veins is the vascular tissue.

Basically the epidermis protects the inner cells of the leaf, but, it is also responsible for other actions such as protection against water loss by way of transpiration { to loose water through vaporisation especially through the stomata of the leaves}. The epidermis covering many leaf species is thinner on the lower surface than on the upper surface. It is built up more on leaves from dry climates as opposed to those that occur in wet climates. The epidermis is covered with pores known as the stomata { from a  Greek word meaning mouth.}

Veins are vascular tissue of the leaf and are situated in a spongy area of the mesophyll. The various patterning  formed by veins is called venation.


Leaf patterning

The various patterns formed by the veins are called venation.
The various patterns formed by the veins are called venation. | Source

Veins have two types of tubes-xylem that brings water  and liquid nutrients from the roots to the leaf while the second type-phloem tubes usually move sap, with disolved sucrose{natural sugars} in the leaf-out of the leaf.

Shape and Texture of Foliage

Now we come to the shape and texture of leaves, for this is an important identifying feature of many species of plants and trees particularly when no flowers are present. foliage is positioned on the twig or stem in various arrangements. Botanist use the term of phyllotaxus to describe these various arrangements. Below are some examples of these arrangements.

Arranged alternately leaf arrangement is alternating along the stem. For example one leaf will face left appearing from a single node, while higher up the stem and on the opposite side the next node will produce a leaf facing to the right.

Arranged opposite--two leaves opposite to each other on either side of the stem.

Arranged in whorls. -three or more leaves produced together at the same node on the stem. 

Goosegrass

The foliage of cleavers {goosegrass} are arranged in whorls
The foliage of cleavers {goosegrass} are arranged in whorls | Source

Arranged rosulate, ie, the leaves form a rosette.

Which ever way the leaves are arranged it is for one principle reason, that is to obtain the maximum light and sunshine on to each of them.

Types of Leaf

The simplest form of a leaf is named just so-a simple leaf. This type of leaf, is to most people, the familiar type. It has an undivided blade known by botanists as the lamina { from Latin meaning thin plate }. However, the shape of the leaf can vary quite a bit by way of lobes.

Nettle foliage

NETTLE FOLIAGE IS THE SIMPLE TYPE. IT ALSO HAS SERRATED TEETH ALONG THE MARGIN
NETTLE FOLIAGE IS THE SIMPLE TYPE. IT ALSO HAS SERRATED TEETH ALONG THE MARGIN | Source

The next type under review is the compound leaf which has a divided blade ,ie, leaflets on opposite side of a central stem which is known as a rachis, from the Greek rakhis meaning a ridge. A good example of a compound leaf is members of the pea and bean family especially the vetches. Unless you have a good knowledge of leaf morphology this group of leaves can be tricky to identify. Compound leaves come in various forms and are named by botanists as follows---

Palmately compound leaves, lobes spread out like fingers on the palm of the hand, good examples are horse chestnut and buckeyes. 

Young horse chestnut leaves

HORSE CHESTNUT LEAVES HAVE PALMATELY COMPOUND LEAVES
HORSE CHESTNUT LEAVES HAVE PALMATELY COMPOUND LEAVES | Source

Pinnately compound have leaflets arranged along the rachis---ODD PINNATE --have leaflets on either side of the rachis in addition they have a terminal leaflet such as the ash tree or rowan tree.   EVEN PINNATE--Lack the terminal leaflet.

Bipinnately --have leaflets that are formed along several branches that spread out from the rachis,thus the leaves are twice divided.

Trifoliate--a pinnate leaf with just three leaflets such as the foliage of clover and laburnum.

Leaves with a prominent stalks are known as petiolated leaves, those that do not are known as sessile leaves{ stalkless}. Then there are clasping leaves -the blade partially or wholly surrounds the stems; some even give the impression that the stem is growing through the leaves, such leaves are referred to as being perfoliate.

The edges of the leaves often referred to as the margins may be fringed with hairs and are termed as being ciliate.

Crenate--having edges that have scalloped or wavy margins from the Latin Crena-a notch; such leaves are lady's mantle and beech.

Margins that are smooth,ie, without teeth or wavy forms are called entire leaves.

Lobate--leaves are such as oaks whose lobes do not reach the center.

Serrate-meaning sawtoothed from the Latin serra -a saw, nettles are a good example of this type of leaf.

Spiny such as holly and thistles.


Various types of Foliage

The lobate foliage of the oak
The lobate foliage of the oak | Source
The compound foliage of vetch
The compound foliage of vetch | Source
The foliage of ash are classed as being Odd pinnate because they have a terminal single leaflet.
The foliage of ash are classed as being Odd pinnate because they have a terminal single leaflet. | Source
SPINY FOLIAGE OF HOLLY
SPINY FOLIAGE OF HOLLY | Source
The trifoliate foliage of clover.
The trifoliate foliage of clover. | Source

In the next article on foliage I will look further at leaf shape. This time looking at the tips, surface and base of foliage and the terminology applied to them.

More by this Author


Comments 6 comments

D.A.L. profile image

D.A.L. 6 years ago from Lancashire north west England Author

Hi cookibuq, thank you for reading and for taking the time to comment. Best wishes to you.


cookibuq profile image

cookibuq 6 years ago from Ireland / Hong Kong

Very informative, will keep an eye out for the different plant characteristics on my next nature walk. Thanks for the posting this :)


D.A.L. profile image

D.A.L. 6 years ago from Lancashire north west England Author

Hi darski thank you for being the first to comment,again!, the tree roots are well down in the soil below the frost level and therefore can take any water they need to see them through until spring. Then the sap will start to rise and the buds will be encouraged to open. Plants especially those in tubs just want enough water to survive, the more water the soil/compost retains the more likely it is to freeze. Thank for rating my friend.Best wishes - Love D.A.L.

LillyGrillzit Thank you so much for your appreciated comments.Best wishes to you.

Kaie Arwen , You are welcome to use it . The whole reason for my writing is to share my knowledge with interested readers and especially the young. Thank you for the compliment and for leaving your kind comment. Best wishes to you.


Kaie Arwen profile image

Kaie Arwen 6 years ago

If you don't mind I'll be printing this and using it in class. It's better written on this subject than our text! Thanks for this ~ Kaie


LillyGrillzit profile image

LillyGrillzit 6 years ago from The River Valley, Arkansas

I love this Hub. I am bookmarking and voted up and sharing. Thank you for sharing your vast knowledge of this foliage! Very smart and intelligent work. I am grateful you wrote this and shared here on HubPages. :0)


Darlene Sabella profile image

Darlene Sabella 6 years ago from Hello, my name is Toast and Jam, I live in the forest with my dog named Sam ...

Wow this is so fantastic and interesting, I had NO idea leaf's were how the tree breaths, our leafs are all gone here in Colorado. The weather is so dry this year, it's really cold but here in the plains, no rain or no snow. How do these sleeping trees survive without water, should we be watering even in the cold weather. I enjoyed this hub and I must say it's one of my favorites and I rate it up up and up even more. Love darski

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