COVENANT UNIVERSITY

Department of Biological Sciences

NAME: OBUEKWE CHUKWUEMEKA AZUBUIKE

MAT NO: 12CQ014230

PROGRAMME: MICROBIOLOGY

COURSE: BLY121(PLANT DIVERSITY:FORMS AND FUNCTIONS)

TOPIC: THE DISTRIBUTION OF HIGHER PLANTS ON EARTH

{DR CONRAD O.A.}

ABSTRACT

Since photosynthesis first became a co-ordinated process, evolutionary development in the

autotrophic world has come a long way — from the prokaryotic blue-green algae to the eukaryotic

angiosperms and gymnosperms, Higher plants have come a long way in becoming the primary

producers on the earth. Plants, with an estimated 300,000 species, provide crucial primary

production and ecosystem structure.

The studies presented in this paper analyse diversity patterns of Higher plants ( ferns, gymnosperms,

and angiosperms) at continental to global scales. A revised version of the earlier world map of

vascular plant species richness and the first maps of species richness of mosses and gymnosperms

on a global scale are presented. Diversity patterns of vascular plants are correlated with different

measures of geodiversity (the diversity of the abiotic environment). Global centres of vascular plant

diversity coincide with highly structured, geodiverse areas in the tropics and subtropics. These are

the Chocó-Costa Rica region, the tropical eastern Andes and the north western Amazonia, the

eastern Brazil, the northern Borneo, and New Guinea, as well as the South African Cape region,

southern Mexico, East Himalaya, western Sumatra, Malaysia, and eastern Madagascar. Constraints

imposed by the physical environment, such as the length of the thermal vegetation period or water

availability, shape large scale trends of biodiversity. However, important centres of species richness

and endemism can only be explained when taking into account the history of the floras. The main

diversity centres in SE Asia are the same for gymnosperms as for all other vascular plants, but in

other parts of the tropics and subtropics there is low gymnosperm diversity. The exceptions to this

pattern are Mexico and California, which have almost as many species of gymnosperms as SE Asia.

VOCABULARY: VASCULAR PLANTS, ANGIOSPERMS, GYMNOSPERMS, TRACHEOPHYTES, SEED

BEARING PLANTS, BIOMES.

INTRODUCTION

Also known as Vascular Plants, Higher Plants evolved about 500 million years ago. They faced a

problem that did not exist for aquatic plants: they needed to live in two different worlds. They

needed to be part of the soil world, to get water, nutrients, and stability, but they also needed to be

in the air, to get sunlight and carbon dioxide. Land plants solved this problem by developing roots as

well as stems and leaves, and a system of vessels (xylem and phloem) to connect them. All four of

the land plant groups have these features (except mosses do not have vessels). Their differences are

seen in whether or not they have seeds or flowers, and in aspects of these features.

The first land plants appeared in the Silurian period of the Paleozoic era. Most botanists connect

them with the origin of the extinct forms of green algae. The transition to a terrestrial existence, to

live simultaneously in two different environments (air and soil) was accompanied by the elaboration

of devices for water supply, protection of reproductive organs from drying out and ensure that the

sexual process. To strengthen the roots in the soil appeared, formed stem with leaves for

photosynthesis in air. In parallel with their development of the differentiation of tissue systems:

developed conductive and mechanical systems of tissues, epidermis and stoma appeared, formed

multicellular organs of sexual reproduction - gametangia. Male gametangia are called antheridia,

they formed the male sex cells (gametes) - sperm or sperm. Female gametangia are called

archegonia, the female gametes are formed - the egg. All devices were expressed in the increasing

divergence in the structure of the gametophyte and sporophyte. In the life cycle of higher plants was

fixed, which occurred even in algae, the alternation of two phases (or generations) - sexual

(gametophyte) and asexual (sporophyte). On gametophyte develop organs of sexual reproduction,

and the sporophyte formed sporangia, within which, as a result of reduction (meiotic) division,

spores are formed from a haploid (n), ie single set of chromosomes.

HIGHER PLANTS: WHAT, WHEN AND HOW?

Higher plants (spread Moss family, Horsetail, lycopsids, ferns, gymnosperms and angiosperms).

However the major higher plants are the Angiosperms and Gymnosperms because of their vascular

system and their external morphology differentiated into true roots, stems and leaves.

There are over 352 000 species of vascular plants in the world. More than 95% of vascular plants are

flowering plants, also called angiosperms (e.g. grasses, orchids, maple trees). The other types of

vascular plants are gymnosperms (cone-bearing trees, e.g. pine trees, spruce trees) and seedless

plants (e.g. ferns, horsetails). 5111 species of vascular plants have been found in Canada. When

excluding species ranked as Extinct, Extirpated, Undetermined, Not Assessed, Exotic or Accidental,

the majority (71%) of vascular plants in Canada have Canada General Status Ranks (Canada ranks) of

Secure, while 13% have Canada ranks of Sensitive, 12% have Canada ranks of My Be At Risk and 4%

have Canada ranks of At Risk. A total of 25 species of vascular plants that used to be present in

Canada are now Extirpated from the country. A large number of species (1252) of vascular plants are

Exotic.

Angiosperm (Latin angi-, “enclosed”; Greek sperma, “seed”) is the common name for the division or

phylum comprising flowering plants, the dominant form of plant life. Members of the division are

the source of most of the food on which humans and other mammals rely and of many raw

materials and natural products. Included in the division are most shrubs and herbs, most familiar

trees except pines and other conifers, and specialized plants such as succulents, parasites, and

aquatic types. The flowering plants (angiosperms), also known as Angiospermae or Magnoliophyta,

are the most diverse group of land plants. Angiosperms are seed-producing plants, such as the

gymnosperms, that can be distinguished from the gymnosperms by a series of synapomorphies

(derived characteristics). These characteristics include flowers, endosperm within the seeds, and the

production of fruits that contain the seeds. Etymologically, angiosperm means a plant that produces

seeds within an enclosure; they are fruiting plants, although more commonly referred to as

flowering plants. The ancestors of flowering plants diverged from gymnosperms around 245–202

million years ago, and the first flowering plants known to exist are from 140 million years ago. They

diversified enormously during the Lower Cretaceous and became widespread around 100 million

years ago, but replaced conifers as the dominant trees only around 60–100 million years ago. The

number of living angiosperm species is estimated to be in the range of 250,000 to 400,000.

Flowering plants (Magnoliophyta) are the most successful of all plant groups in terms of their

diversity. The group includes more than 250,000 species, and at least 12,000 genera. This group is

usually referred to as angiosperms because, as their name implies, their seeds are enclosed in a

carpel (in a vessel). The carpel is the primary feature that distinguishes angiosperms from

gymnosperms. Angiosperms live in all terrestrial and aquatic habitats on earth. Except for conifer

forests and moss-lichen tundras, angiosperms dominate all the major terrestrial zones of vegetation.

Gymnosperms are primitive seed plants. They have a long evolutionary history. The earliest

gymnosperms appeared in the Paleozoic and became the dominant plants worldwide during the

Mesozoic and Caenozoic periods. Many species of existing gymnosperms emerged in the Tertiary

Period, then went through the Glacial period and survived and multiplied till now. The total number

of living gymnosperms of the world is about 850 species, belonging to 79 genera of 15 families.

Although the number of species of gymnosperms accounts for only 0.36% of that of the

angiosperms, they have formed large areas of various kinds of coniferous forests and are widely

distributed all over the world, especially on mountains from middle to alpine latitudinal zones in

cold-temperate and subtropical latitudes of the Northern Hemisphere. Gymnosperm (Latin gymn-,

“naked”; Greek sperma, “seed”) is the common name for any seed-bearing vascular plant without

flowers. There are several types: the cycad, ginkgo, conifer, yew, and gnetophyte. Gymnosperms are

woody plants, either shrubs, trees, or, rarely, vines (some gnetophytes). They differ from the other

phylum of seed plants, the flowering plants (Angiosperm), in that the seeds are not enclosed in

carpels but rather are borne upon seed scales arranged in cones. The gymnosperms are the most

ancient seed plants; they appear to have arisen from fern ancestors in the Devonian Period. Cycads

retain the most primitive characters of the extant seed plants. Gnetophytes are considered from

morphological and molecular evidence to share a common ancestry with the flowering plants. Living

gymnosperms are distributed worldwide, with a majority, particularly the conifers, in temperate and

subarctic regions. Cycads and gnetophytes are mainly tropical to subtropical. There are about 70

genera with 600 species of living gymnosperms, far less than many families of flowering plants.

Scientific classification: Gymnosperms are contained in four phyla: Cycadophyta, Ginkgophyta,

Pinophyta, and Gnetophyta.

THE EVOLUTIONARY BRIGDE

The Green Algae are the cradle of the higher plants. In other words, they are regarded as one end of

an evolutionary bridge — with the higher plants being the other. But where in the higher plants did

the bridge span to? The Bryophyta are frequently regarded as the most elementary of land plants.

Some, however, would doubt this. It is perhaps unfortunate that because of its ubiquity Marchantia

is often the only liverwort that elementary botanical textbooks consider in any detail, and many

people may have formed the idea that this bryophyte is the most elementary of higher plants. In

reality it is quite advanced among the bryophytes because, for example, it has barrel-pores, which in

some species can to some extent open and close like stomata; well-developed air-chambers with

photosynthetic filaments the presence of archegoniophores and antheridiophores (both of which

are highly specialised structures); two kinds of rhizoids — smooth and peg-walled. So maybe when

we are thinking of the bryophytes as the place among the land plants to which we connect our

evolutionary bridge, we should not keep Marchantia too much in the forefront: rather, we should

think of something a little less advanced — e.g. Riccardia, Pellia.

Others would prefer to consider that the bridge should be connected to the simplest known vascular

plants — the Psilophytales. Such folk think that at least some of the bryophytes may have been

derived from this group, for it is known that even those psilophytalean examples which have

survived the rigours of fossilisation were not quite so far removed from the hornworts

(Anthocerotales) or maybe even the mosses and liverworts as one might at first suppose. In other

words Bryophytes could have been derived from the Psilophytales and as such might be regarded

more properly as a red herring in the present conception of the continuum of plant evolution. But

even though bryologists and pteridologists cannot give any clear-cut indication of what constituted

the first thoroughgoing land plant, they all agree that the ultimate origin of the Tracheophyta seems

to lie within the Chlorophyta. He who subscribes to a monophyletic origin of the land plants sees this

‘hypothetical ancestral form (or forms) somewhere between the Chlorophyta and the most primitive

known extinct Psilopsida but he knows it to be as yet a “missing link” unsupported by concrete fossil

evidence.’ Irrespective of what were in fact the bridging organisms between the Green Algae and

the most primitive land plants, it cannot be denied and one must never lose sight of the fact that at

no time earlier or later in the evolution of the Plant Kingdom was such a momentous evolutionary

transition set in motion as when those early members of the Plant Kingdom began to move from an

aqueous to a terrestrial environment.

BIODIVERSITY

The variety of life on Earth and its biological diversity is commonly referred to as biodiversity. `The

regions that contain similar ecological species groups create ecological groups that are

homogeneous habitats with similar ecologic and floristic composition, which can be used in habitat

classification. With development of restoration ecology and understanding of principles of

biodiversity, it is realized that species composition and diversity are fundamental characteristics of

ecosystems and vegetation diversity should be considered. Plant species distribution over a high

geographical range is controlled by climatic factors, mainly temperature and rainfall. Over a small

range, however, species distribution is related to edaphic factors The number of species of higher

plants and not just higher plants but also their lower counterparts, animals and microorganisms, the

enormous diversity of genes in these species; the different ecosystems on the planet such as

deserts, rainforests and coral reefs are all part of a biologically diverse Earth. Biological diversity

means the variability among all living organisms from all sources including inter alias, terrestrial,

marine and other aquatic ecosystems and biological diversity within a species and of ecosystems.

Biodiversity is the degree of variety in nature and not nature itself.

Out of the 1.4 million known species of living organisms only about 2,50,000 are higher plants and

1.03 million are animal (WWF, 1989). According to another estimate, worldwide there are 2,70,000

known species of vascular plants (Table-1).

Taxonomic Group Number of Species

Bacteria 3,600

Blue green algae 1,700

Fungi 46,983

Bryophytes 1,700

Gymnosperms 750

Angiosperms 2,50,000

Global patterns of angiosperm diversity

Even though the map presented in Fig.1 shows species richness of all vascular plants, the patterns

mainly reflects angiosperm diversity. Fig.2 shows that the absolute maximum of gymnosperm

diversity peaks at less than 60 species per 10,000 km2. The proportion of fern species within floras

reaches maxima of approximately 15% only on some oceanic islands or in montane rainforests (see

below). Thus, 85 to 99% of the patterns shown in Fig. 1 are patterns of angiosperm diversity. Areas

representing global maxima of vascular plant species richness are the Chocó-Costa Rica region,

tropical eastern Andes and north western Amazonia, eastern Brazil, northern Borneo, and New

Guinea, as well as the South African Cape region, southen Mexico, East Himalaya, western Sumatra,

Malaysia, and eastern Madagascar. In general, regions of high geodiversity especially in mountain

areas of the humid tropics and subtropics, harbour the highest species numbers. A comparison of

species richness of biomes, shows that tropical broadleaf forest reaches species numbers up to

10,000 species per 10,000 km2, e.g., in the mountain ranges of Costa Rica (Davis et al. 1997) or c.

5,000 species on 1,200 km2 at the Mt. Kinabalu, Borneo. These absolute maxima are closely linked

to mountainous areas. However, also lowland forests, e.g., in the western Amazon basin, harbour

very high plant diversity. A high number, 473, of tree species and a total of 1,000 vascular plant

species are documented in 1 ha lowland rainforest in the Amazonian part of Ecuador (Valencia et al.

1994), and 3,000 species have been found in 24 ha in Chribibiquete-Araracuara-Cahuinarí region of

Colombian Amazon (Davis et al. 1997). Tropical and subtropical coniferous forests and

Mediterranean climate areas are also very species rich. In contrast, Tundra and Taiga regions

harbour lowest mean species richness, whereas absolute minima can be found in hyperarid areas of

the Sahara and Atacama desert, as well as in Arctic and Antarctic environments.

FIG. 1

Global patterns of gymnosperm diversity

Though new genera are still being described, the gymnosperms might be one of the best

documented groups of Higher plants. However, until now, there has been no global map of total

gymnosperm diversity. Thus, in Fig. 2 we present a first draft of a species richness map of all

gymnosperms at the global scale. The most important centres of gymnosperm diversity are located

in SE Asia. Especially the forests of the Chinese provinces of Yunnan and Sichuan with almost 60

species co-occurring on an area size of 10,000 km2 are very species rich. Other centres with more

than 30 species per 10,000 km2 are SE China in general (with more than 100 species in total), New

Caledonia, northern Borneo with Mt. Kinabalu, the central range of New Guinea, southern Mexico,

and California. Large areas of the southern hemisphere harbour no or only few gymnosperm species.

Exceptions are New Caledonia with more than 40 species, eastern Australia, Tasmania, and New

Zealand, the South African Drakensberg area, and parts of the South American Andes.

FIG. 2

The largest contiguous coniferous forests of the world, the northern hemisphere boreal forests or

taigas, harbour only few species with only 5 to 10 species co-occurring in an area of 10,000 km2.

Less than 15 species in total can be found in the almost 10 Mio. Km2 in Siberia. Only few

gymnosperm species are found in tropical Africa. The whole continent harbours 90 species, which

are mainly concentrated in southern Africa and the Mediterranean. There are, e.g., only two species

documented for West Tropical Africa and less than 15 species in the rainforests of the central Congo

basin. Areas without or with very few species are large parts of the Sahara, southern parts of the

Arabian penninsula, the western part of the Amazon basin and parts of the Cerrado and Caatinga

regions in South America, and the central dry lands of Australia.

GEOGRAPHICAL DISTRIBUTION OF HIGHER PLANTS

The study of the geographical distribution of plants over the earth is one of the most profound

interest, not only to the botanist but to mankind in general. To the former it is of especial interest on

account of the intimate relations existing between it and the origin of the different species of plants.

It is a trite remark that although there may be places identical in temperature, in soil, in humidity,

and other circumstances governing the stations of plants in both North America and Europe, and in

South America and Africa, still it does not necessarily follow that the species of plants in these

identical localities are alike or even at all similar. Indeed, researches show it to be rarely or never the

case. In almost every country, however, there seems to be a certain though sometimes a small

proportion of plants which are found in other and distant parts of the world, Where we find an

isolated example of a group of plants existing in one country, while its nearest congeners are in

another perhaps thousands of miles off, we naturally feel interested in trying to discover the cause

of this wide separation, and the means by which the plant has reached its present location. The

geographical distribution of higher plants is one of the most difficult and important subjects

connected with the study of plants. Before it can be well organized it will be necessary to bring

together very many more observations of plants in all parts of the world than is possible now.

However, a few facts are known which are both interesting and suggestive. In order to make their

presentation as definite as possible, this section of the term paper will be restricted to a brief

account of the geographic distribution of vascular plants.

One of the two great groups of vascular plants is known as the Gymnosperms, a group which in our

region is represented by pines, spruces, hemlocks, cedars, etc. In the tropics the group is

represented by a very different type of trees, known as the Cycads. They resemble in general habit

tree-ferns, or palms. The group of Gymnosperms with which we are acquainted have been called

Conifers on account of the very characteristic cones which they bear. Several principles connected

with geographic distribution may be illustrated by considering briefly these two groups of

Gymnosperms. The Cycads are absolutely restricted to the tropics, a few forms reaching into semi-

tropical conditions, as in southern Florida. If a comparison be made between the eastern and

western tropics, it will be discovered that the Cycads are almost equally divided between, the two

regions. For an unknown time, but certainly a very long one, these eastern and western Cycads have

been separated from one another. As a consequence they have become so unlike that one kind of

Cycad is never found in both hemispheres. Their long separation from one another, and their

somewhat different conditions of living has resulted in working out differences of structures which

botanists recognize as species, genera, etc. The Conifers, on the other hand, are characteristic of

temperate regions. If the distribution of Conifers were indicated upon a world map, there would be

shown a heavy massing of them in the northern region and a lighter massing in the southern region,

the two being separated from one another by a broad tropical belt. This tropical belt is traversed in

just two places; one is by means of the East Indian bridge, across which certain Australasian forms

reach China and Japan; the other is the chain of the Andes mountains, along which a single northern

type has, worked its way into the southern part of South America, The two great masses of Conifers,

therefore, lie in the northern and southern hemispheres, rather than in the eastern and western

hemispheres, as is the case with the Cycads. This long separation has resulted just as it did with the

Cycads; that is, the northern and southern Conifers are not any longer alike, but differ so widely

from one another that botanists cannot discover any form which is common to both the northern

and southern hemispheres, excepting the single one already mentioned, which has succeeded in

crossing the tropics by means of the Andes bridge. Another interesting fact in connection with the

distribution of the Conifers is that their great centers of display are in regions which border the

Pacific Ocean, and they have often been spoken of as a Pacific group. There are three special centers

of display; one is the China-Japan region, a second is the general Australasian region, and the third is

western North America just why this border region of the Pacific is especially favorable for this sort

of plant life is a question which we do not as yet pretend to answer. Another fact which illustrates

this persistent distribution in connection with the Pacific is that in the case of the Conifers which

belong to the southern hemisphere, the continental masses which pair in the display of similar forms

are Australia and South America. Another fact, which is true of all large groups, is that certain forms

have a very extensive distribution, and others are very much restricted in their occurrence. For

example, the greatest genus of Conifers is the genus made up by the pines, at least seventy kinds of

which are recognized. This great genus sweeps throughout all the north temperate regions of the

globe. There is a similar extensive distribution of the different kinds of spruce, larch, juniper, etc. On

the other hand, the giant redwood, known as Sequoia, is restricted to certain comparatively small

areas in California. In China and Japan, and also in Australia, there are numerous illustrations of

forms very much restricted in their occurrence.

Nigeria harbours rich diversity of vascular plants having 285 families (42 ferns and fern allies, 5

gymnosperms, and 238 angiosperms), 1541 genera, and 5029 species (including 183 intraspecific

taxa consisting of 45 subspecies, 133 varieties, and 5 forms). Leguminosae, Poaceae, Rubiaceae,

Orchidaceae, and Cyperaceae are the largest 5 families. Primitive families of angiosperms are quite

scarce excepting the aquatic Nymphaeceae. The 243 seed plant families consist of 171 tropical

families, 56 cosmopolitan families and 16 temperate families, the tropical elements are absolutely

dominant.

ECOLOGICAL DISTRIBUTION OF HIGHER PLANTS AND MAJOR BIOMES

It is a trite remark that although there may be places identical in temperature, in soil, in humidity,

and other circumstances governing the stations of plants in both North America and Europe, and in

South America and Africa, still it does not necessarily follow that the species of higher plants in these

identical localities are alike or even at all similar. Indeed, researches show it to be rarely or never the

case. In almost every country, however, there seems to be certain though sometimes a small

proportion of plants which are found in other and distant parts of the world.

Biomes of the World

Ecologists divide the Earth’s ecosystems into biomes; regions in which the dominant vegetation has

a distinctive growth form. Growth form is the outward appearance or shape of the leaves or body of

a plant. For example, tree, grass, and shrub are different plant growth forms. Trees and shrubs can

be further subdivided into evergreen or deciduous, and broadleaf or needle-leaf (coniferous) growth

forms. Ecologists recognize at least ten different biomes. The world’s major land biomes include

tropical rain forest, tropical dry forest, tropical savanna, desert, temperate grassland, temperate

woodland and shrubland, temperate forest, northwestern coniferous forest, boreal forest, and

tundra. Each of these biomes is defined by a unique set of abiotic factors – particularly climate – and

has a characteristic higher plant ecological community.

Global distribution of major terrestrial biomes (Adapted from PhysicalGeography.net © Dr.

Michael Pidwirny, University of British Columbia – Okanagan).

Tropical Rain Forest

Tropical rain forests are home to more species than all other land biomes combined. The leafy tops

of tall trees – extending up to 70 meters above the forest floor – form a dense covering called a

canopy. In the shade below the canopy, a second layer of shorter trees and vines forms an

understory. Organic matter that falls to the forest floor quickly decomposes and the nutrients are

recycled.

Dominant higher plants: broad-leaved evergreen trees; ferns; large woody vines and climbing plants,

orchids and bromeliads.

Eco- Geographic distribution: parts of South and Central America, Southeast Asia, parts of Africa,

southern India, and northeastern Australia.

Tropical Dry Forest Tropical dry forests grow in places where rainfall is highly seasonal rather than

year-round. During the dry season, nearly all the trees drop their leaves to conserve water. A tree

that sheds its leaves during a particular season each year is called deciduous. The areas associated

are generally warm year-round; alternating wet and dry seasons; rich soils subject to erosion.

Dominant higher plants: tall, deciduous trees that form a dense canopy during the wet season;

drought-tolerant orchids and bromeliads; aloes and other succulents.

Eco-Geographic distribution: parts of Africa, South and Central America, Mexico, India, Australia, and

tropical islands.

Tropical Savanna

Receiving more seasonal rainfall than deserts but less than tropical dry forests, tropical savannas, or

grasslands, are characterized by a cover of grasses. Savannas are spotted with isolated trees and

small groves of trees and shrubs. Compact soils, fairly frequent fires, and the action of large animals

such as rhinoceros prevent some savanna areas from turning into dry forest warm temperatures;

The area is characterised by seasonal rainfall; compact soil; frequent fires set by lightning.

Dominant high plants: tall, perennial grasses; sometimes drought-tolerant and fire resistant trees or

shrubs.

Eco-Geographic distribution: large parts of eastern Africa, southern Brazil, northern Australia.

Desert

All deserts are dry in fact, a desert biome is defined as having annual precipitation of less than 25

centimeters. Beyond that, deserts vary greatly, depending on elevation and latitude. Many undergo

extreme temperature changes during the course of a day, alternating between hot and cold. The

organisms in this biome can tolerate the extreme conditions.

Dominant higher plants: cacti and other succulents; creosote bush and other plants with short

growth cycles

Eco-Geographic distribution: Africa, Asia, the Middle East, United States, Mexico, South America,

and Australia.

Temperate Grassland

Characterized by a rich mix of grasses and underlaid by some of the world's most fertile soils,

temperate grasslands – such as plains and prairies – once covered vast areas of the midwestern

United States. Since the development of the steel plow, however, most have been converted to

agricultural fields. Periodic fires and heavy grazing by large herbivores maintain the characteristic

plant community

Dominant High plants: lush, perennial grasses and herbs; most are resistant to drought, fire, and cold

Eco-Geographic distribution: central Asia, North America, Australia, central Europe, and upland

plateaus of South America.

Temperate Woodland and Shrubland This biome is characterized by a semiarid climate and a mix of

shrub communities and open woodlands. In the open woodlands, large areas of grasses and

wildflowers such as poppies are interspersed with oak trees. Communities that are dominated by

shrubs are also known as chaparral.

Dominant Higher plants: woody evergreen shrubs with small, leathery leaves; fragrant, oily herbs

that grow during winter and die in summer.

Eco-Geographic distribution: western coasts of North and South America, areas around the

Mediterranean Sea, South Africa, and Australia.

Temperate forests

They contain a mixture of deciduous and coniferous trees. Coniferous trees, or conifers, produce

seed-bearing cones and most have leaves shaped like needles. These forests have cold winters that

halt plant growth for several months. In autumn, the deciduous trees shed their leaves. In the spring,

small plants burst out of the ground and flower.

Dominant plants: broadleaf deciduous trees; some conifers; flowering shrubs; herbs; and a ground

layer of ferns.

Geographic distribution: eastern United States; southeastern Canada; most of Europe; and parts of

Japan, China, and Australia.

Northwestern Coniferous Forest

Mild, moist air from the Pacific Ocean provides abundant rainfall to this biome. The forest is made

up of a variety of conifers, ranging from giant redwoods, along the coast of northern California. To

spruce, fir, and hemlock farther north. Moss often covers tree trunks and then forest floor.

Flowering trees and shrubs such as dogwood and rhododendron are also abundant. Because of its

lush vegetation, the northwestern coniferous forest is sometimes called a "temperate rain forest.."

Dominant plants: Douglas fir, Sitka spruce, western hemlock, redwood.

Geographic distribution: Pacific coast of northwestern United States and Canada, from northern

California to AlaskaBoreal Forest.

Boreal Forest

Along the northern edge of the temperate zone are dense evergreen forests of coniferous trees.

These biomes are called boreal forests, or taiga Winters are bitterly cold, but summers are mild and

long enough to allow the ground to thaw. The word boreal comes from the Greek word for "north,"

reflecting the fact that boreal forests occur mostly in the Northern Hemisphere.

Dominant plants: needleleaf coniferous trees such as spruce and fir; some broadleaf deciduous

trees; small, berry-bearing shrubs

Geographic distribution: North America, Asia, and northern Europe

Tundra The tundra is characterized by permafrost, a layer of permanently frozen subsoil. During the

short, cool summer, the ground thaws to a depth of a few centimeters and becomes soggy and wet.

In winter, the topsoil freezes again. This cycle of thawing and freezing, which rips and crushes plant

roots, is one reason that tundra plants are small and stunted. Cold temperatures, high winds; the

short growing season, and humus-poor soils also limit plant height

Dominant plants: ground-hugging plants such as sedges, shrubs and short grasses.

Geographic distribution: northern North America, Asia, and Europe.

Global Vascular plant distribution in relation to topography, soils, micro-climate and other

influencing factors.

Topography, soils, climate, disturbance, herbivory and competition can affect distributions of higher

plant species and hence community composition (Körner 2003). In mountain systems, climate can

have a major effect on vegetation. As a result, most communities have been identified as being

particularly at risk from predicted changes in climate (Grabherr et al. 2000; Walther et al. 2005).

With increasing temperatures and changes in snow cover regimes predicted for many regions

around the world (Hennessy et al. 2003; Pauli et al. 2007; IPCC 2007; Van de Ven et al. 2007), it is

important to determine the relative importance of environmental factors including climate on

current vascular plant composition within and among the various eco-geographical habitats of the

world.

Over the past few decades there has been increasing concern about the effects of human activities

on the natural environment (McNeill 2001). Lately, because of urban and agronomy development,

forests and rangelands destruction and natural changes, some of these higher plants are reported as

extinct species It became clear that ecosystem interference largely predates the 20th century and

that it has far reaching consequences beyond the major industrialised areas of the world (Crosby

1972; Richards 2003; Simmons 1989; Turner et al. 1990). Along with the effects of habitat

destruction, nutrient loading is one of the most important threats to plant diversity, leading to

declines of distribution area and even regional extinction . If climatic factors such as temperature

and precipitation change in a region beyond the tolerance of a species phenotypic plasticity, then

distribution changes of the species may be inevitable. There is already strong evidence that plant

species are shifting their ranges in altitude and latitude as a response to changing regional climates.

When compared to the reported past migration rates of plant species, the rapid pace of current

change has the potential to not only alter species distributions, but also render many species as

unable to follow the climate to which they are adapted. The environmental conditions required by

some species, such as those in alpine regions may disappear altogether. The result of these changes

is likely to be a rapid increase in extinction risk. Adaptation to new conditions may also be of great

importance in the response of plants. Predicting the extinction risk of plant species is not easy

however. Estimations from particular periods of rapid climatic change in the past have shown

relatively little species extinction in some regions, for example. Knowledge of how species may

adapt or persist in the face of rapid change is still relatively limited. Changes in the suitability of a

habitat for a species drive distributional changes by not only changing the area that a species can

physiologically tolerate, but how effectively it can compete with other plants within this area.

Changes in community composition are therefore also an expected product of climate change.

The winds undoubtedly exercise an immense influence on the distri- bution of plants. Many seeds

are furnished with a pappus or feathery appendage, by means of which they are easily carried along

by the wind. Many of these belong to the Composite, such as the dandelion, the thistles, hieraciums,

etc. Others are provided with wings, as in the ash and the maple ; still others with cottony or

feathery tails, as in the anemones and clematis. Again, many are so minute as to be visible to the eye

only in the form of smoke, and are so numerous as to be almost uncountable.

CONCLUSION

The appearance of a plant group in a given area isn’t accidental, but occurs in response to changes in

climatic, topographic, edaphic and biotic parameters. In fact, vegetation groups are determined by

the combined effects of a whole range of ecological factors. Thus, change in the soil, topography and

grazing factors can lead to vegetation responses in each area of the landscape .The regions that

contain similar ecological species groups create ecological groups that are homogeneous habitats

with similar ecologic and floristic composition, which can be used in habitat classification. Higher

Plant species distribution over a high geographical range is controlled by climatic factors, mainly

temperature and rainfall. Over a small range, however, species distribution is related to edaphic

factors. Unfortunately, nowadays higher plant species conversation is less considerable on a global

platform.

REFERENCIES/BIBLIOGRAPHY AND LITERATURE CITATIONS

PATTERNS OF VASCULAR PLANT DISTRIBUTION AT CONTINENTAL TO GLOBAL SCALES

Jens Mutke , Wilhelm Barthlott(2008)

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THE GREEN ALGA: CRADLE OF THE HIGHER PLANTS(Tuatara; vol 23, issue3)

H.W. johston,( Botany Department, Victoria University of Wellington, NZ)

VASCULAR PLANT DISTRIBUTION

C.M. Pickerg, K Green,( school of environment, griffith university, australia)

PLANT PHYLOGENY AND PHYTOGEOGRAPHY

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DIVERSITY AND DISTRIBUTION OF VASCULAR PLANTS IN NIGERIA

Abiodun E. Ayodele(university of Ibadan, Ibadan), Yong yan(institute of botany, the chinese

academy of sciences)

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RELATIONSHIP BETWEEN ENVIRONMENTAL FACTORS AND PLANT DISTRIBUTION

Salman Zare, Mohammad Jafari(Faculty of Natural Resource, University of Tehran, Iran)

MAJOR BIOMES OF THE WORLD-TEACHERS DOMAIN

www.teachersdomain.com

GLOBAL PATTERNS AND DETERMINANTS OF VASCULAR PLANT DIVERSITY

Holger Kreft, Walter Jetz(Nees Institute for Biodiversity of Plants, University of Bonn)