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Saturday, January 28, 2006

Types of Trees

1. Angiosperms vs. Gymnosperms

Trees are scientifically divided into two major categories: angiosperms and gymnosperms.
Angiosperms are flowering plants and their seeds are encased in a protective ovary. This division contains the larger number of species can be further subdivided into dicots and monocots. Dicots have two seed leaf structures and include many broadleaf trees such as the elm, maple and oak. Monocots have one seed leaf structure and include species such as the palm.

Gymnosperms, on the other hand, do not produce flowers. Their seeds have structures such as cones, rather than a protective ovary. Conifers (needle-leaf trees) are a major group of gymnosperms.

2. Deciduous vs. Coniferous

Trees can also be divided into deciduous and coniferous categories.

Deciduous trees are also known as broadleaf trees because the leaves are generally larger and wider than those of conifers. The larger leaf size means a greater surface area for photosynthesis, but it also mean the leaf is too fragile to withstand winter conditions. Therefore, most deciduous trees drop their leaves in autumn.

Coniferous trees keep their leaves throughout the year, shedding only the oldest leaves. Usually these leaves are lower down on the tree and do not receive as much sunlight as newly developed leaves higher up. Some of the best-known members of the conifer family are pines, spruces, firs, and hemlocks. The cones of the conifers are its flowers.

3. Tropical Trees are grown in warmer climates. In tropical rain forests trees grow very tall. They are trying to get sunlight. Palm trees are mostly found in the tropics. The coconut palm produces a large nut with a liquid "milk". Another tropical tree is the eucalyptus. These trees are fast growing. They like dryer conditions and are found in the outback and subtropical areas of Australia.

Friday, January 27, 2006

Reproduction of Gymnosperms

A group of plants called gymnosperms developed wind borne pollen. These were trees -- cycads, ginkos and needle-bearing trees such as pines and redwoods. Tall plants get more wind than those close to the ground, and the gymnosperms developed small male pollen-bearing cones. Their pollen was released into the air and drifted to other trees in the forest. Today, if you are in a pine forest in spring, you can often see a golden haze of pollen grains in the air.

The plants also developed female cones which are essentially ovaries. The pollen falls directly on the female cones, and the pollen grains grow tiny tubes into the ovary to find the chromosomes and join with them. The female cone grows into the cones that we are familiar with, and the seeds are tucked safely between the bracts.

Gymnosperm means naked seeds. These seeds have only a very thin covering that probably does not offer them much protection.

Wind pollination seems rather extravagant, as surely most of the pollen grains never find a female cone. However, the system works, and has worked for millions of years. Gymnosperms grow in forests and groves, where the tall individual plants grow close together, so there are many potential targets for the pollen grains.

Wednesday, January 25, 2006

The Development of Flowers

A new group of plants, the angiosperms, appeared about 110 million years ago. These plants had developed a number of structural innovations, the most striking of which is the flower. Flowers enchant us with their beauty, delicacy, and variety of form, but they represent a very practical development. Plants, by growing flowers and fruit, formed partnerships with animals who provided transportation for pollen and seeds.

Some flowering plants still use wind to transfer their pollen to other plants. The grasses, growing thickly together in meadows and on plains, continue to rely on wind pollination.

Many flowering plants, however, use insects or birds to distribute their pollen. Insects can be lured to the flowers by a few drops of sweet nectar. Brightly colored petals guide the insects toward the nectar and pollen. Bees can fly for several miles in a day, and, if all members of a plant species come into bloom at about the same time, the bees spread their pollen far and wide. Pollen sticks to the hairy bodies and legs of insects, and is easily carried away. Many of the fruits that we eat are dependent on insect pollination.

Another invention of the Angiosperms is the development of the seed coat on their seeds. Each seed is enclosed in a tough little covering to help it to survive in the world until conditions favor successful germination and development..

Tuesday, January 24, 2006

Illustration of Plant Life Cycle

Monday, January 23, 2006

How Plants and Flowers Grow

Picture showing anatomy of a flower

Plants can be divided into two types: flowering plants and non-flowering plants. The are many flowering plants such as the rose, daisy, tulip and others. Non-flowering plants include coniferous trees such as the pine and spruce.

Both types of plants follow a similar process of growth. Plants have both male pollen and female parts of the flower. Pollen from a plant is carried by the wind, or by insects, to fertilize the female parts of the plant. Once fertilized, a cone or seed is produced that is capable of creating a new plant.


  • A fruit is a ripened ovary - it contains the seeds
  • Often the fruit is edible
  • There is a wide variety of fruit types - but all fruits are basically formed from a ripened ovary
  • A seed is a ripened or mature ovule
  • Often the seed is edible - this serves the same function as do edible fruits
  • There is a wide variety of seed types
  • A vegetable is an edible part of a plant that is not part of the reproductive organs (edible roots, stems, leaves, etc.)

Wind Pollination

Many plants, such as grass, weeds and even large pine trees, rely on the wind for pollination. The pollen is small and light, allowing it to be blown by the wind. The pollen lands on other plants a fertilizes them.

Insect Pollination

Worker bees collect pollen and nector from flowers in order to create the wax they need to build their hive. The queen bee creates the wax in her abdomen, which she uses to build chambers or cells where she lays her eggs.

In the process of building their hive, bees play a very important role pollenating flowers and plants. As a bee gathers nectar from a flower, tiny grains of pollen will stick to its hairy legs and body. When the bee flies to another flower for nector, the pollen on its legs and body brushes off to help furtilize the flower.


Since most plants cannot travel from place to place, they rely on animals and the wind to scatter their seeds.

Seeds come in a wide variety of sizes, from small flower seeds to large acorn seeds and pine cones.


Many plants and flowers reproduce from bulbs. The parent plant produces buds or bulbs that split off and start to grow a new plant.

Sunday, January 22, 2006

Plant Reproduction

Asexual Reproduction

Some plants can grow from cut off leaves or stems. Many of our house plants are shared this way. Some plants even grow little plants on their leaves or root when a piece of stem is buried.

All these methods of reproduction work well. However, they do not make it possible for plants to move to new locations. They result in plants with the same characteristics as the parents: the same resistance to the same diseases, the same responses to flood, drought, heat and cold, and the same schedules of growing. They are vulnerable to everything that might destroy the parents. A viable community needs members with diverse strengths and vulnerabilities.

In addition to reproducing asexually, most land plants also reproduce sexually.

Sexual Reproduction

Once plants got out of the water and onto the land, they faced real challenges. One of those problems was to invent ways to share and to scatter genetic material. Some of the early plants, ferns, for instance, found ways to exchange reproductive material in water, and later released many tiny spores into the air. However, much of the earth is too dry for this strategy. Plants had to find ways to deal with the dry air.

Saturday, January 21, 2006

How Plants Reproduce

Plants have two methods of reproduction, asexual reproduction and sexual reproduction.

Asexual reproduction is cloning. A piece of a plant may root or sprout and grow into a new plant which is genetically identical with the parent.
  • Sexual reproduction results in a new plant which contains genetic material from two parents, but which is not genetically identical with either one. These new plants may be able to adapt more successfully to environmental changes than their parents could.

To live and multiply on land, plants needed to evolve new structures and methods for reproduction. An important advance was the development of the flower, a structure which allowed widespread scattering of its pollen and yet provided a stable, nurturing environment in the ovary for developing seeds. Pollen could be carried from flower to flower by insects, the wind, or, sometimes, birds.

The seed was another important innovation, as significant for plants as the amniotic egg was for land animals. Seeds would form when the chromosomes of the parents were united in the ovary. A seed is a compact package made of a cell capable of growing into a plant, food to help the plant get started, and, in angiosperms, a seed coat that protected the seed from dehydration and damage in the environment. Properly protected seeds could survive until conditions favored their development. In the deserts today, some seeds may lie dormant for many years until the rains come and provide conditions in which the seeds may germinate and grow into plants. Some seeds also are contained in, or attached to, structures which help the seeds to be carried to other places that may be suitable for them.

Flowering Plants Reproduction

Questions on Plants Reproduction

Friday, January 20, 2006

Leaf Shapes and Arrangements

Picture of Leaf Shapes

A tree's leaf is one major marker that helps in keying out and identifying any species of tree. Most trees can be identified by the leaf alone.

As you can see in the illustration, leaves come in many shapes and sizes. The "star" shape of sweetgum is totally different from the heart-shaped leaf of an eastern redbud. Note that leaves can be described by observing their base, their margin and their tip or apex. Each characteristic has a name and is used a part of the identification process.

Also a leaf can either be simple (no extra leaflets) or compound (three or more leaflets). On a compound leaf, all leaflets are attached to a single leafstem or rachis.

Leaf Tips: These can be rounded, pointed, or take on other forms.
  • Attenuate: a sharp-pointed apex with concave margins that form an angle less than (<) 45 degrees.
  • Acuminate: a sharp-pointed apex with straight or convex margins that form an angle less than (<) 45 degrees.
  • Acute: an pointed apex with margins that form an angle between 45 and 90 degrees.
  • Obtuse: a blunt apex with margins that form an angle greater than (>) 90 degrees.
  • Rounded: an curved apex with margins that form a smooth arc.
  • Caudate: an attenuate apex with a slender tail-like appendage at the tip.
  • Cuspidate: an acute apex with a stiff tip or cusp.
  • Mucronate: with a small extension of the midrib barely extending beyond the blade apex.
  • Emarginate: with a shallow depression at the apex, not exceeding ? of the distance to the centre of the leaf blade
  • Truncate: a broad, flat apex, abruptly ending at right angles to the midvein.
  • Retuse: a rounded summit with a shallow depression at the apex, not exceeding 1/16 of the distance to the centre of the leaf blade.
  • Obcordate: apex with prominent, rounded lobes, cut ? to ¼ of the distance to the centre of the leaf blade.
  • Cleft: apex divided into rounded or straight-margined lobes, cut ¼ to ½ of the distance to the centre of the leaf blade.

Thursday, January 19, 2006

Leaf Shapes

Leaf shapes:
These can be flat, broad leaves.

The leaves can be thin and narrow as pine needles.

The leaf shape can be scaley like cedars.

Leaf Margins: These can be smooth, toothed or lobed.

Palmate leaves
(picture on left ) :These can take on several forms, having a shape similar to that of a hand with the fingers extended and having three or more veins, leaflets, or lobes radiating from one point.

Pinnate leaves ( picture on right ) They resembling a feather; having parts or branches arranged on each side of a common axis.

Pictures of Leaf Shapes

Leaf shapes of trees

Leaf Morphology

Wednesday, January 18, 2006

Function of Leaf

Each plant has a basic limb, branch, and leaf structure that has been adapted by this plant's to meet it's habits. A conifer will have thin leaves to reduce water and sun requirements The habits of trees make it possible to identify and classify each tree.

What are leaves?

To a plant, leaves are
food producing organs. Leaves "absorb" some of the energy in the sunlight and takes in carbon dioxide from the surrounding air in order to create photosynthesis.

The green color of leaves, in fact, is caused by a pigment "chlorophyll" that is the specific chemical agent that acts to capture the sunlight energy needed for photosynthesis. The products of photosynthesis are sugars and polysaccharides. An important "waste product" of photosynthesis is oxygen.

Leaf Shapes on tree leaves

The shape of a tree's leaves are a response to the tree species' long term ecological and evolutionary histories. Understanding of the "logic" behind the varied forms of leaves is facilitated by a firm grasp of the precise functions a leaf must accomplish.

1. A leaf must "capture" sunlight for photosynthesis (and as it does this it may also absorb a great deal of heat!)

2. A leaf must take in carbon dioxide from the surrounding air. When these leaf stomatae are open to allow the uptake of carbon dioxide, water from inside the leaf is lost to the atmosphere.

3. The leaf, then, is affected by these balancing acts: enough sunlight and carbon dioxide to run photosynthesis, but not too much associated heat absorption or water loss. The shape and design of the leaf is to adjust for the plant requirements.

Leaves high in the tree canopy receive a great deal of sunlight and tend to be smaller in size. Needle-shaped leaves have a very low light absorptive surface area and also have a very thick, outer cuticle coating and is not able to capture very much sunlight energy for photosynthesis and is designed to prevent excessive water loss.

Tuesday, January 17, 2006

Why Trees have Different Shapes

There are many reasons why tree shapes differ. A tree growing in poor soil may be stunted due to lack of nutrients, and a tree growing right next to an apartment building may have more leaves on the side facing the sun. Different kinds of trees have their own unique form, but the form that any tree has is also affected by the environment where it grows.

Sunshine and water are both essential for a tree to survive, and both influence tree height, crown shape (for example, a round treetop or the cone shape of a pine tree), and the form of leaves.

Some tree species grow quite tall and receive much sunlight. But what about those trees left in the shadows? Many trees collect sunlight that is filtered through the leaves of taller trees. These shaded understory trees survive by gathering indirect sunlight or sun flecks that break through openings in the canopy. A rounded crown seems to work best for gathering filtered, understory sunlight, which comes from many different directions.

The shape of the tree's crown also has a lot to do with where it lives. Nearer to the equator, the noontime sun is almost directly overhead all year. Tall trees with flat treetops (or crowns) are very common in this part of the world because the flat shape helps expose more of their leaves to the direct, overhead light.

Up nearer to the Arctic circle, the sun is never directly overhead and is usually quite low in the sky. Trees in this part of the world tend to be cone-shaped (think of pine trees), with leaves from the top of the tree to the bottom, to make the most of this sunlight.

Finally, many of the trees up nearer to the Arctic circle (like spruce, pines, and fir trees) have needles, partly because needles are especially adapted to cold, dry climates. Needles retain water better than broad-leafed trees like oaks and maples.

Monday, January 16, 2006

Facts about Trees II

Bristlecone Pines grow at high elevations on soils developed from carbonate rocks. The trees can survive for more than 4,000 years in these difficult conditions, where almost nothing else can grow. This tree is in the White Mountains in California's Basin and Range Province.

Tree Biology

  • Trees are the longest living organisms on earth.
  • Trees and other plants make their food through a process called photosynthesis.
  • The inside of a tree is made of cork, phloem, cambium, and xylem.
  • The xylem of a tree carries water from the roots to the leaves.

Trees and the Environment

  • Trees renew our air supply by absorbing carbon dioxide and producing oxygen.
  • Two mature trees can provide enough oxygen for a family of four. One tree produces nearly 260 pounds of oxygen each year.
  • One acre of trees removes up to 2.6 tons of carbon dioxide each year.
  • Shade trees can make buildings up to 20 degrees cooler in the summer.
  • Trees lower air temperature by evaporating water in their leaves.
  • Tree roots stabilize soil and prevent erosion.
  • Trees improve water quality by slowing and filtering rain water, as well as protecting aquifers and watersheds.
  • The cottonwood tree seed is the seed that stays in flight the longest. The tiny seed is surrounded by ultra-light, white fluff hairs that can carry it on the air for several days.

Record-Setting Trees

  • One of the tallest soft wood trees is the General Sherman, a giant redwood sequoia of California. General Sherman is about 275 ft or 84 m high with a girth of 25 ft or 8 m.
  • The 236 ft or 72 m high Ada Tree of Australia has a 50 ft or 15.4 m girth and a root system that takes up more than an acre.
  • The world's tallest tree is a coast redwood in California, measuring more than 360 ft or 110 m.
  • The world's oldest trees are 4,600 year old Bristlecone pines in the USA.

Picture: The General Sherman tree (
Sequoiadendron giganteum) in Sequoia National Park
is the largest living thing on earth. This tree measures 31 m (101.5 feet) in circumference at its base, and is 83 m (272.4 feet) tall, and has a total estimated weight of 6,167 tons.

Sunday, January 15, 2006

Facts about Trees I

Picture of Acer japonicum Aureum


  • Trees keep our air supply fresh by absorbing carbon dioxide and producing oxygen.
  • In one year, a single tree can absorb as much carbon as is produced by a car driven 26,000 miles.
  • Trees provide shade and shelter, reducing yearly heating and cooling costs by 2.1 billion dollars.
  • Trees lower air temperature by evaporating water in their leaves.
  • The average tree in metropolitan area survives only about 8 years!
  • A tree does not reach its most productive stage of carbon storage for about 10 years.
  • Trees cut down noise pollution by acting as sound barriers.
  • Tree roots stabilize the soil and prevent erosion.
  • Trees improve water quality by slowing and filtering rain water as well as protecting aquifers and watersheds.
  • Trees provide protection from downward fall of rain, sleet, and hail as well as reduce storm run-off and the possibility of flooding.
  • Trees provide food and shelter for wildlife.
  • Trees located along streets act as a glare and reflection control.
  • The death of one 70-year old tree would return over three tons of carbon to the atmosphere.

Trees and Science

  • Dendrochronology is the science of calculating a tree's age by its rings.
  • Tree rings provide precise information about environmental events, including volcanic eruptions.
  • A mature birch tree can produce up to 1 million seeds per year.
  • Moon trees were grown from seeds taken to the moon by Stuart Roosa, Command Module pilot of the Apollo 14 mission of January 31, 1971. The effort included 400-500 seeds, which orbited the moon on the first few days of February 1971. NASA and the USFS wanted to see if being in space and in the moon's orbit would cause the seeds to grow differently than other seeds.

Classification of Tree

Saturday, January 14, 2006

Song That Teaches Plant Growth

A Plant Will Grow

My plants are growing, from the seeds down in the ground
Soon they'll be showing how the plant world gets around
Just plant a seed, and when you're done
Give it air and water and lots of sun
And in a couple of weeks or so,
You know a plant will grow!

A seed sprouts a root, isn't that cute?

My plants are growing, from the roots and the seeds down in the ground
Soon they'll be showing how the plant world gets around
It grows some roots, which uncoil
To soak up nutrients from the soil
And in a couple of weeks or so,
You know a plant will grow!

Plants grow a stem, every one of them!

My plants are growing, from the stems to the roots from the seeds down in the grownd
Soon they'll be showing how the plant world gets around
At first just a tiny stem is seen
You know it's growing 'cause it's green
And in a couple of weeks or so,
You know a plant will grow!

Look what the stem achieves - it's growing some leaves!

My plants are growing,
from the leaves to the stems to the roots from the seeds down in the ground
Soon they'll be showing how the plant world gets around
The leaves get bigger by the hour
Then it might grow fruit, it might grow a flower
And in a couple of weeks or so,
You know a plant will grow!

From the fruit or the flower
to the leaves
to the stem
to the roots
from the seeds down in the ground

And now you know - just how a plant will grow!

Life Cycle of Pumpkin

Plants Life Cycle - good educational site

Life Cycle of Bean Plant

Illustration of Life Cycle of Plant Life cycle of plant - Flash Quiz

Friday, January 13, 2006

Life Cycle of Plant

A plant's life cycle describes how long a plant lives or how long it takes to grow, flower, and set seed.

Plants begin their life as a seed. With water, right temperature and right location, the seed germinates. It becomes a seedling. Roots push down into the ground to get water and minerals. The stem reaches for the sun, and leaves begin to unfold. A bud appears. The plants then produce flowers. The flowers are then pollinated in many ways – by bees, moths, butterflies, insects, moths, bats, butterflies and even by the wind. The pollinated flower turns into fruit. The new seeds are inside the fruit. The ripe fruit drops to the ground and the cycle begins again.

Plants can be either an annual, perennial, or biennial.

tomato plant Annual

A plant that completes its life cycle in one growing season. It will grow, flower, set seed, and die.

    Examples: marigolds, tomatoes, and petunias.

roses Perennial

A plant that lives for 3 or more years. It can grow, flower, and set seed for many years. Underground parts may regrow new stems as in the case of herbaceous plants, or the stems may live for many years like woody plants (trees).

    Examples: daisies, chrysanthemums, and roses.

carrots Biennial

A plant that needs two growing seasons to complete its life cycle. It grows vegetatively (produces leaves) one season, goes dormant or rests over the winter, and then grows flowers, sets seed, and dies the second season.

    Examples: parsley, carrots, and foxglove.

Tuesday, January 10, 2006


The scientific or botanical name
of a plant is the means by which we give it its unique place in the scientific and biological world. Begun by Carolus Linneaus, a Swedish botanist, in the eighteenth century, this name is binomial (has two parts), consisting of genus and species, both of which are expressed in Latin. The genus or generic name is a noun which usually names some aspect of a plant, such as Coffea, the Latinized form of the Arabic word for beverage, kahwah. The species or specific name is usually an adjective that describes the genus. In the case of coffee, the species is arabica, indicating that the plant was thought to originate in Arabia. The coffee plant botanical name, Coffea arabica, refers to only one plant and cannot be confused with any other. Its botanical name is unique to that particular plant the world over.

The botanical name is often followed by a letter or letters which stand for the botanist who named that plant. The coffee plant's complete botanical name is Coffea arabica L., the L. standing for Linneaus. If the original botanical name of a plant is later changed, the original classifier is still noted in parentheses. Other often used abbreviations are Sarg. for Charles Sprague Sargent, founder of Harvard University's Arnold Arboretum; Lam. for Jean Baptiste Lamarck, French evolutionist and botanist; and Audub. for John James Audubon, ornithologist, naturalist, and painter. (Interestingly, this convention of naming the discoverer is not found in the naming of animals.) Sometimes the Family name is included, which groups the genera. It can usually be distinguished by its ending--"eae."

Linneaus's book Species Plantarum (The Species of Plants), published in 1753, continues to influence the naming of plants today. It is the starting point for checking whether a name has been used previously to insure that each plant is given a unique name. The earliest name for a plant is usually the official name should a dispute arise.


The genus and species names often tell something about the plant. They can describe the appearance of the plant, reflect the common name of the plant, indicate a chemical present in the plant, tell how the plant tastes or smells, or describe how the plant grows. The genus or species name can honor someone, a botanist, a person in power, someone historically prominent. The name can reflect the country or origin of a plant.

For example, Erythroxylum coca, the plant from which we derive cocaine, is named after erythro meaning red and xylo meaning wood, literally "red stem." (Coca, the species name, is the common name of the plant.) The jaborandi tree Pilocarpus jaborandi has a genus name which indicates that the alkaloid pilocarpine can be extracted from the plant. The species name jaborandi means "one who makes saliva or one who spits," referring to the use of the plant as an expectorant.

Plant classification can be painstakingly difficult. Plant species can resemble one another quite closely; plants can sometimes interbreed within species or across species, producing hybrids and varieties that complicate classification. A case in point is the cinchona tree, a plant instrumental in world history as a result of its alkaloid derivative, quinine, which helped to reduce the incidence of the terrible disease malaria. The cinchona tree, with its many species and hybrids and varieties within species, has resisted absolute classification. It's ambivalent ways have left botanists puzzled as to the exact number of species which exist. In fact, one species grouping of cinchona has been labeled 'Cinchona officinalis.' Officinalis (meaning 'of the workshop') is a common species name used for many medicinal plants, particularly, it seems, under the trying circumstances of difficult taxonomy.

Monday, January 09, 2006


Science classifies living things in an orderly system through which they can be readily identified. Living things are grouped into categories of increasing size, based upon relationships within those categories. For example, all plants can be put in order from the more primitive to the more advanced. Such a ranking would look like this:

Plant Kingdom

Bryophytes: Small with leaflike, stemlike, and rootlike structures.

Disseminated by spores: mosses, liverworts, hornworts.

Vascular Plants: Larger with true leaves, stems, and roots.

  1. Seedless: Ferns, horsetails, club mosses.

  2. Seed Plants:

    1. Gymnosperms: Usually have cones, no flowers, seeds not enclosed in fruit: pines, spruces, firs, hemlocks, cycads, ginkgo.

    2. Angiosperms: Have flowers, seeds enclosed in fruit

      1. Monocotyledons: Leaves have parallel veins, one seed leaf: grasses, orchids, lilies, palms.

      2. Dicotyledons: Leaves have netted veins, two seed leaves: cherry trees, maples, coffee, daisies, etc.

This informal way of describing plant classification gives an overview of how plants are classified. Botanists use a more complex system. A botanist divides the plant kingdom into Divisions, similar to the Phyla used to divide the animal kingdom. There are twelve divisions. Referring to the above ranking, three of these divisions are Bryophytes, four are seedless plants, four are Gymnosperms, and one is Angiosperms. Each Division is further divided into Classes, which are divided into Orders, which are divided into Families, which are divided into Genera (singular, Genus), which are divided into species, which is the "basic unit" of classification. Put somewhat simply, individuals in a species are able to breed with each other, while in broader categories individuals do not interbreed.


Despite the great advances made in botany, there are many, many plants yet to be discovered, classified, and utilized; unknown plants are treasures waiting to be found. Today's ethnobotanists are combing regions of the world, looking for tomorrow's medicines and food crops. They are exploring the functional properties and relationships of plants within ecosystems to help us to understand the need for diversity in the way we manage our plant resources.

The plant world, our world, is in constant flux. Due to human and other factors, we are seeing the possibility of extinction for many plants and animals. Plant classification aids in keeping track of our planet's endangered inhabitants. Just as importantly, we are realizing the need to understand ecological systems which preserve biodiversity. Today's scientists are exploring how genetic diversity and ecological sensitivity are necessary in solving such problems as feeding the population and fighting disease. Plant classification is vital to these endeavors. As is plain to see, a name is not just a name.

Sunday, January 08, 2006

Classification of Plants

The most important method of classification has been standardized among botanists for centuries. This method attempts to formulate groupings based upon the evolutionary characteristics inherited genetically among related species. This method uses information from genetics, biochemistry, developmental biology, paleobotany, morphology, anatomy, physiology. Related groups should share evolutionarily-derived characteristics. A natural classification would have very few characteristics that appear to evolve multiple times in related groups. Thus our goal in botanical classification is to arrive at a natural classification that involves the fewest evolutionary steps. If we are successful then groups with the most shared characteristics will naturally be classified closely together.

All living organisms can be divided into a few major kingdoms. The kingdoms commonly recognized include: Archaea and Bacteria (the prokaryotic kingdoms), Protista, Fungi, Plantae, and Animalia. Those organisms that carry out photosynthesis include the cyanobacteria in kingdom Bacteria, the algae in kingdom Protista, and the plants in kingdom Plantae.

Each kingdom is composed of plants of at least some similar organisms. Plantae. for example, holds mosses, ferns, conifers, and flowering plants. Because these groupings are quite distinct from each other, the kingdom is divided further into phyla (singular: phylum). Thus Plantae includes the phyla bryophyta (mosses), pterophyta (ferns), coniferophyta (conifers), and anthophyta (flowering plants). Plants within each phylum share certain important features. For example the anthophyta reproduce by means of flowers including having their ovules enclosed in carpels.

Nevertheless a phylum includes plants with some fairly fundamental differences, so it requires further subdivision into classes. Among the flowering plants we find two major groups: those with a single seed leaf and those with two seed leaves. These differences are accompanied by several other morphological and other differences that divide the flowering plants into the classes: monocotyledonae (monocots) and dicotyledonae (dicots).

Each class is divided into orders, and each order is divided into families, and each family into different genera. Each genus is divided into a range of particular species. Thus the classification is a nested series of categories as follows:

Kingdom --> Phylum --> Class --> Order --> Family --> Genus --> Species

Each species has a scientific name which is a Latin binomial. The binomial is composed of the genus name and the specific epithet (the add-on name of the species). For example the human binomial is Homo sapiens. We are in the genus Homo (meaning self!), and the specific kind of homo that we are is the one that can think rationalize (sapient!). Please note that our name is Homo sapiens whether we speak of one human or the entire population. There is no such thing as a "Homo sapien."

You might wonder why we choose Latin for our binomials. Well, Latin is a dead language; no one speaks it any longer, so its definitions do not change over time! This reduces confusion drastically. For example, a brightly colored plant named a century ago might have been called "gay" if English were the language of binomials. But today that epithet might lead a scientist to wonder whether this meant something about the plants reproductive biology. The definitions in Latin are static. The second reason we choose Latin is that it has become universal among scientists worldwide...preventing much confusion.

"Black-eyed Susan" is an English common name for over 100 species of plants, depending upon which part of the world you come from. Scientists cannot use that name in their research as this would be very confusing. However Rudbeckia hirta is a black-eyed susan about which there is no confusion. If you open a journal written in Chinese characters, right there in the title will likely be a Latin bionomial to help you decide whether to have it translated or not.

Plant binomials are often despised by non-scientists as hard to remember. Yet, they aren't too difficult in many cases if you can simply dissect out the root words. Rosa is the genus name for roses. So Rosa multiflora is a rose that has multiple flowers in each cluster. Rosa grandiflora is a rose with very large flowers. Rosa floribunda produces many flowers over a long summer season...abounding in flowers.

People have modifed some species quite drastically and so having a binomial is sometimes insufficient to describe the specific plant being used. A good example is Brassica oleracea, the mustard of the garden. Europeans long ago prized this plant that grew rapidly in the cool and short summers of norther Europe. To make this plant more diverse as a source of food, they selected from the ancestral (wild) plants plants that showed different characteristics. Through selective breeding they created several different food plants from this single important species. Because these are subdivisions of a natural species, we had to create a subdivision beneath species! This is called variety. Brassica oleracea can now be found in these varieties:

Brassica oleracea capitatacabbage
Brassica oleracea acephalakale
Brassica oleracea gemmiferaBrussels sprouts
Brassica oleracea italicabroccoli
Brassica oleracea botrytiscauliflower
Brassica oleracea caulorapakohlrabi

Of course any perusal of a seed catalog will show that even this is insufficient. The cabbages, for example, exist in dizzying array of different cultivated varieties (cultivar). There is Brassica oleracea capitata 'Late Flat Dutch' and Brassica oleracea capitata 'Copenhagen Market' to name just two examples. You will notice that the cultivar name is given in the "home language" and is put within single-quotes, while the binomial and any botanical variety names are in Latin italics.

Classification of Plants

Friday, January 06, 2006

Classifying Plants

Plant classification is one of the older pastimes in botany. Every culture, society, and religion has taken it as its duty to name and organize the plants in its area into some manageable arrangement. The arrangement at first was meant to facilitate communication between people about the plants under discussion.

The earliest organizations, naturally, were based upon the uses of plants by people. Obviously some plants were useful as vegetables, others were fruits, some make great spices for other foods, some were a good source of sugar, or perhaps starch. Oils could be extracted from others. Some were good for spinning fibers into thread for clothing. Yet others were ornamental.

But as is true of any classification scheme based upon human uses, there are problems of several sorts. The uses of plants by one civilization might not be the same as those by another. Even among individuals in the same society, one person's fruit is another's animal fodder. Moreover there is the conundrum of what to do with plants that present several different uses. George W. Carver demonstrated many uses for peanuts. Henry Ford produced an automobile with body parts made of soybean products. But the worst problem with human-use classification is that it puts related organisms in different classification categories. There is no relationship between the classification system and the evolutionary pathway through which the diversity was obtained.

Other early attempts at classification focused upon the form of the plant. Thus one category would be the herbs; here we use herb in its botanical sense meaning non-woody plants. A second category would be woody plants. These plants have secondary xylem and would need to be subdivided into several sub-categories of form: shrubs, vines, and trees. Each of these categories would have to be subdivided into deciduous and evergreen. Of course whether an evergreen vine is closer related to an evergreen tree or to a deciduous vine is a very good question. An of course there are both woody and herbaceous vines. It is sounding messy. Also, we find that a natural grouping have members in all of these "unnatural" categories.

Humans have also noticed that the seasonality of plants varies and forms another way to divide up the plants into categories. Thus in one category we have annual plants which are planted in the spring, flower that summer, and die in the fall. Then we have the perennial plants which are planted in one year, grow vegetatively in the first year, overwinter, and then flower in each year thereafter. Nurseries like to sell annuals because they know customers will come back next year to replace them all. They sell an entire flat of annuals for a small price. Perennials are planted, and then never replaced, so nurseries place a premium price upon them. However, there is a real "gotcha" among the perennials in some nurseries, however...biennials act like perennials in the first and second year, but die all the way to the ground at the end of that second year. You will have to replace those. Many seed catalogs are divided into annual and perennial categories. However even a casual gardener will be able to find plants of the same kind in both the annual and perennial categories. Certain species of a genus may be perennial, and other species of the same genus may be annual. It is not a natural breakdown.

Another way of dividing the plants is obvious in nursery catalogs: by climate. Tropical plants originate in areas of the world between the tropics of Cancer and Capricorn. This part of the world is very warm year-round with frost never occurring in the year. This is explained as the sun passes directly overhead on at least one day each year, and may do so for much of the year. Tropical plants generally cannot withstand any kind of frost. Subtropical plants are slightly more hardy and can tolerate light frost but not heavy freezes. Hardy plants can tolerate frozen periods of various durations and temperatures. The hardy plants are classified on the basis of hardiness zones. In North America these range from Zone 1 (extremely cold and long winters) to Zone 10 (no frost at all). Subtropical plants survive in zones 8-10. Some hardy plants can only survive in the warmer zones (7-10) while others are tough enough to survive in zones 1 and 2! In nursery catalogs the coldest zone for each plant is noted and gardeners are well-advised to heed those. Connecticut is zone 6 except for the northwest corner which is zone 5. Along the shore one might experiment with some zone 7 plants if a sheltered spot is available. However, again, close relatives can be tropical plants and extremely hardy plants. This is not a natural classification scheme. It is useful but not based upon genetics and evolution, the cornerstones of biology!

Thursday, January 05, 2006

The Plant Kingdom (Plantae)

Plants provide nourishment for our bodies and souls. With the help of protists and fungi, plants provide the oxygen we breathe and the food that sustains us -- either directly or indirectly, by feeding other animals. Plants provide shade over our heads and cool carpets under our feet while surrounding us with beautiful colors and marking the change of seasons.

Prominent plants give us a handle on ecological communities. Descriptions such as "Redwood-Tanoak Forest" or "Oak Grassland" indicate not only the plants we may find there but the animals, fungi, and climate as well.

Classification of the plant kingdom can be especially confusing to the amateur naturalist. For example, according to modern botany:

  • A palm tree has more in common with a blade of grass than with other trees.
  • A strawberry plant is more closely related to an apple or apricot tree than to a clover or geranium.
  • A Ginko (Maidenhair) tree is so different from other plants that it is in a phylum by itself. But if you have to group it with other plants, it belongs with conifers such as Pine trees.

At least four classification systems are in common use: Plants are classified into 12 phyla or divisions based largely on reproductive characteristics; they are classified by tissue structure into non-vascular (mosses) and vascular plants (all others); by "seed" structure into those that reproduce through naked seeds, covered seeds, or spores; or by stature divided into mosses, ferns, shrubs and vines, trees, and herbs.

All of these higher-level groupings are decidedly lopsided: the vast majority of the 270,000 plant species are flowering herbs.

Sunday, January 01, 2006

Introduction to Kingdom Plantae

Picture of a typical plant cell

The plant kingdom, one of four eukaryotic kingdoms, is composed of multicellular, autotrophic organisms that photosynthesize to fix inorganic carbon (from atmospheric CO2) into organic molecules. Plants are the foundation of all terrestrial habitats, and serve as terrestrial Earth’s primary autotrophs, making organic molecules that will cycle through the food webs of most ecosystems. The photosynthetic capabilities of plants ultimately allow all terrestrial members of the animal kingdom to survive.

One hallmark of plant cells is the cell wall, which, in contrast to cell walls of single-celled organisms, is made of cellulose. The cell walls provide support for plant cells, as well as support and cohesiveness for plant tissue. Unlike the plasma membrane, the cell wall is not a semipermeable membrane, and so the shared cell walls between adjoining plant cells must have openings, plasmodesmata, to allow material transport and communication. Another distinguishing feature of plant cells is the large central vacuole, which stores a water reserve as well as essential chemicals, waste products of cellular metabolism, and sometimes other species-specific functions, such as storage of poisons or flower pigments. The central vacuole can also aid in cell growth by absorbing water.

Excluding a few photosynthetic protists and cyanobacteria, plant cells are the only cells that contain chloroplasts. These organelles carry out the processes of photosynthesis, converting light energy into chemical energy and storing it as sugar. As well as producing food for ecosystems, photosynthesis releases oxygen molecules as byproducts, which replenish atmospheric oxygen used in cellular respiration and form a layer of ozone, O3, which shields the earth from solar ultraviolet rays.

Plants probably evolved from multicellular green algae called charophytes and were the first multicellular organisms to colonize land. In order to do this, plants had to evolve several new characteristics in the form of distinct, specialized organs, which protists and algae lack. First of all, plants need to have a form of anchorage in the ground and rigid stem tissue for support. Thus, plants have developed root structures, which, in addition to anchoring a plant in the ground, allow the plant to take up chemical nutrients from the soil.

A 3D Picture of a plant cell

Cellulose-containing cell walls developed in plant cells to maintain a form of rigidity in the part of the plant above ground. These account for the stiffness of plant stems and from the hardness of wood. Marine algae, which are suspended in water and can absorb nutrients from all around, have neither of these structures. Also, to prevent water loss in a terrestrial environment, plants evolved a waxy cuticle, which covers stem and leaf surfaces. Gases for photosynthesis can not diffuse across this cuticle, so tiny pores called stomata are present in the cuticle.

Because plants have organs that serve different functions, they must have systems to distribute necessary substances throughout the plant. Sugars, produced in photosynthesis, must be distributed to the body and roots of the plant that do not photosynthesize. Water and nutrients from the soil, taken up by the roots, must also make their way into the plant body and leaves. To perform these essential functions, plants contain a vascular tissue network, which consists small tubes running throughout the plant. There are two types of vascular tissue: xylem, which are small tubes dead cells that transport water and minerals up from the roots, and phloem, which are living cells that distribute sugars produced in photosynthesis.

Also characteristic of plants, as well as some algae, are gametangia that protect gametes. These are pockets of cells that protect the egg cell, and where the egg is fertilized.

Plants have a life cycle unlike that of any animal, fungus, or bacteria. Probably a trait inherited from protistan (algal) ancestors, diploid and haploid generations alternate in plants, meaning that one species will often take two very different forms. In the alternation of generations, the reproductive cells of the diploid plant, or sporophyte, will undergo meiosis, creating haploid spores. Each spore can undergo mitotic divisions that will eventually form a gametophyte, or a haploid plant. The gametophyte’s reproductive cells divide mitotically to produce haploid gametes, which fuse to become a diploid zygote. The zygote grows into a sporophyte, and the process repeats. Typically, the two types of generations have different forms, and one is dominant over the other, which is smaller and grows on the dominant plant. In most plants, the sporophyte generation is dominant; for example, in pine trees, the tree is a sporophyte plant while the small cones are gametophytes.

The predominant plant divisions (the same taxon level as the animal phyla) include, in the order in which they probably evolved, the bryophytes (Division Bryophyta), the ferns ( Divsion Filicophyta ), the horsetails (Divsion Sphenophyta ), the gymnosperms (Divsion Coniferophyta), and the angiosperms (Division Anthophyta), as well as the ginkgoes (Divsion Ginkophyta).

Bryophytes, the mosses, are the only among these to have a dominant gametophyte generation, with sporophytes that grow on top of the gametophytes and contain a sporangium, similar to the gametangium of most plants, that protects the haploid spores. The seedless vascular plants, which include such organisms as the fern and the horsetail, have small gametophytes that grow on the bottom of the sporophytes. In these plants, as in mosses, the unprotected sperm require moisture to travel to the egg, where fertilization occurs. This is somewhat of a limiting factor in their spread, and the reason why these plants are usually found in areas near water or with excessive rain. The third major division of plants, the gymnosperms, consists of conifers and such plants that have sperm made by pollen grains. The dominant sporophyte generation, the tree, produces cones that contain the gametophytes.

Angiosperms, the most recent evolutionary branch of the plant kingdom, are the flowering plants that now dominate the plant world (80% of all plant are angiosperms). The success of the angiosperms lies centrally in the flower, the key part of the reproductive cycle. The flower contains the gametophytes, and controls production of sperm and eggs. Embryos, which are created in the flower, become encased in seeds, which protect the embryos. Seeds are in turn contained by fruits, which facilitate seed distribution, either by wind or animal consumption (the seeds will pass through animal digestive tracts).

The plant kingdom, one of Linnaeus’s original two, occupies a fairly solid place in modern taxonomy. The only major debate, right now, is on whether the charophytes, the algal ancestors of plants, should be classified in the plant kingdom. They share many similar features, but all algae are currently recognized in the Kingdom Protista.

Hence, the Kingdom Plantae has immense diversity, and its organisms are the foundation of the cycles of energy on Earth as well as the fixation of organic carbon, the basis for all life.