Prepared by Mwl Skylight Lucas From Sokoine university of Agriculture second year education

1. Prepared by mwl skylight lucas
INTRODUCTION.
The origin and early evolution of plants on land it based on interval of plants life from a simple
to complex, gradually. The origin and early diversification of land plants involve specialized
sexual organs, stems, structural tissues (wood), epidermal structure for respiration and gaseous
exchange (stomata), leaves, roots and spore bearing organs . This Paleozoic eras divide into the
several periods, according to their distinctive characteristics such as Ordovian , Silurian ,
Devonian , and Permian . Within periods there were several epoch evidenced on origin and
diversification of land plants has come mainly from dispersed spore and mega fossils.These
epochs were Eoembrophytic , Eotracheophytic and Eutracheophytic.Then the evolution of the
Angiosperms or flowering plants, they become the dominant species in the world, although
flowering plants was the last and recent group to evolve about 300 million years later than the
first vascular plants called pteriophytes and in 220 million years later than the seed plants known
as gymnosperms. The flowering plants now is the most dominant group of the most vascular
plants in the world accounting between 300 and 400 families and 250,000 and300,000 species as
compared to approximately 10,000 species of pteridaphtes and 750 species of gymnosperms.
Therefore evolution of flowering plants is considered as an evolutionary interest;
Evidence on the origin and diversification of land plants has come mainly from dispersed
spore and mega fossil. Pattern in the easily fossil record recognized by three new plant based on
epochs . The following are the pattern in the fossil record
EOMBRYOPHYTIC (Mid _Ordovian early lanvirn _476 Million Years ago to the Silurian 432
Million years.)
In period of mid ordovian the spore tetrads appeared overbroad geographic area ,also provides
good evidence of land plants. The combination of decay resistant wall ( imply the presence of
sporollennin ) and tetrahedral configuration (imply haploid meiotic products) is diagnostic of the
land plant.
In late Silurian and Devonian mega fossils as well as data of the spore wall ultrastructure and the
structure of fossil , cuticles , support previous suggestion of the land flora of liverworts like
plants . Some early spores and cuticles may also represents extinct transitional line ages between
charophycean algae and liverworts. So due to that charophycean algae and liverworts are seen to
the to be the plants products coilbi n this period and are member of eoembryophytic .
EOTRACHAEOPHYTIC (early Silurian 432Myrs to early Devonian 402Myrs)
Early Silurian marks the beginning of a decline of a decline in diversities of tetrads rise to a
dominance of individually dispersed , simple spore which are found. In several basal land such
horn roots , some mosses and early vascular plant. Although tetrads remain dominant in some
early Devonian localities from North Western Europe , the elaboration of simple spore and
turnover of spore species provide evidence of increasing land plants diversity and vegetation

2. change . Although spore have been observed in Silurian , mega fossils , the most dispersed from
remain unknown indicating that substantial land plant diversity is currently un detected in the
mega fossil records. Data from N.Europe , Siberia , Podolia southwestern Ukraine) , Libya,
Bolivia Australia and Xinjiang and Yunnan (china) document increasing land plant diversity into
the base of the Devonian.
EUTRACHEOPHYTIC
This was the period of early Devonian 398M years to Mid Permian 256M years where spores
and Mega fossil increased dramatically. At that period it was where eutracheophytes become
more complex with true vascular tissues (xylem and phloem) such as ferns , conifers , and
flowering plants compared to Eotracheophytic periods the plants were classified into three
groups
a) ccoksonoids example cooksonia
b) Lycophytes example clubmosses
c) Euphyllophytes example fern
During the eutraphytic period the plants it was able to adapt in harsh condition like drought
where it has long roots for absorption of water in the ground as well as shedding of leaves to
avoid desiccation as well as they have the ability to undergo alternative generation where byboth
gametophyte phase and sporophyte phase.

3. BUILDING A LAND PLANT
Origin of land plant originated from the charophycean green algae this is due to phylogenetic
studies. The fresh water origin of plants seems likely but direct evidence from fossil records
which is inclusive as mid –paleozoic charophytes are found in both fresh water and more
commonly marine farcies.

4. These charophycean green algae had ability to produce spore pollen , cutin , phenotic compounds
and the glycolate oxidase pathway. During the transitions of absences of well developed
saprophytes, gametophytes with sexual organs of land type , cuticle and non motile , air borne
sporopollenin walled spore were evolved. Also in this period of transition from an aqueous to a
gaseous medium exposed plants to new physical conditions that resulted in physical change and
structural changes.
Phylogenetic studies predict that early land plants were small and morphological simple, thus
early fossil bears a strong resemblance to the simple spore producing phase of living mosses and
liverworts. The gaseous exchange surface and sexual organs seems to have been primary
responses to life on land. This changes land to highly differentiated plants with stomata, multi
cellular, sexual and spore bearing organs, water conducting and other tissues system. This
morphological differentiation occurred in both phases of life cycle includes gametophyte phase
and saprophytes phase
EARLY TERRESTRIAL ECOSYSTEM.
 The earliest terrestrial ecosystem is firstly described by the exisistence of the land plants
 Early vascular plants (which have modified prostrate stem bearing rhizoids resembling
those of living bryophytes (evolved in early Devonian)
 More substantial roots capable of anchoring large trees evolved independently in several
group during the middle to late Devonian
 Biosynthesis of lignin and the origin of lateral meristems in those group resulting in
stratified forest communities. by the end of middle Devonian trees evolved independently
in several major group resulting in stratified forest community
 The early evolution of lignin decomposing fungi (some are ascomycetes and
basidomycetes) is still poorly understood but this group would have been essential for
recycling much of the organic carbon.
 The earliest land plants probably encountered terrestrial ecosystem that has been
occupied by Bacteria and protists ,algae, lichens and fungi since the late proterozoic.
 Some of the plants such as enigmatic plants like protosalvinia,grew in late Silurian and
the early Devonian about 400 millions years and some of the largest elements may have
been fungi which may have been extracted in the Silurian and early Devonian sediments .
 The discovery of fungi arbusculae in early Devonian megafossils confirms that
endomycorrhizal association were an important innovation in the colonization of land.
 By the end of megascopic plants which appeared to have colonized the land only once,
many animals groups made the transition to terrestrial existence independently and
overcome the problems of water relations n different ways like centipedes ,collembolans
and some of possibly bristle tails.
 Available evidence indicates that these animals were mainly predators and detrivores and
until the appearance of vertebrates herbivores in the latest palazoezoic. These arthropod
fauna are known from several localities in north America germany and united kingdom.
These fauna proves the tissues of some fossils plant.

5. FUTURE DIRECTION.
 The fossils records of spores combined with phylogenetic studies indicates that groups
related to living bryophytes were early colonizer of land. bryophytes eg moss, liverwort ,.
This suggest that several linage of vascular plants had already evolved by the mid
Silurian. The megafossils of land plants however appears much later and in these
assemblages there is a conspicuous bias toward the recognition and perhaps
representation of vascular plants. The source of data of early megafossils has been the
northern europian region and siluan megafossils are from marine sediments
 This seem onset of continental conditions in the Devonian of northern Europe allowed
megafosssils to be preserved at a time when vascular plants were well established but still
diversifying, rapid appearance of vascular plants lead to changes in geological condition
due to Rapid biological diversification
 Paleontological is the evidence shows that major group of living land plants are relicts
(some remains and others died) even though much modern species diversity within these
groups may have been evolved . Such combined studies of living and fossils plants
provide an improved basis for comparative studies at plants development. This indicates
for example that ontogeny of leaves and spore bearing in clubmosses are likely to share
substantial similarities but are unlikely to exhibit common features with leaves in seed
plants such as spore bearing organs ,stems ,stomata and sexual organs are each under the
same kind of development control in all groups
 Generally more data are needed to explore this issue further on molecular basis of plant
development from a broader selection of land plants.
THE FIRST PLANTS.
The earliest bacteria were probably heterotrophs single celled organisms that were incapable of
manufacturing their own food instead they digested other bacteria through the use of enzymes
andfermentation reactions.
The next step was the evolution of autotrophs single celled bacteria that are capable of
manufacturing their own food through various chemical reactions and there is three major types
of autotrophic bacteria this are
1. Nitrifying bacteria which use ammonia to manufacture their food.
2. Sulphur bacteria which use hydrogen sulphide to manufacture their food
3. Photosynthetic bacteria this use carbon dioxide and sunlight to manufacture their food,
this type of bacteria are known as photoautotrophs since the basic reaction they use is the
same reaction today used by plants.
The next major development occurred simultaneously with evolution of eukaryote was
development of large cells with enclosed nuclei that propagated through sexual reproduction and

6. the most accepted hypothesis for this development is that one prokaryote assimilated another
without actually digesting and this was symbiotic relationship at first. Those eukaryotes
containing assimilated photoautotrophs are likely the ancient ancestors of the plants.
The first photosynthetic eukaryotes were chlorophyte which today include green algae they
would like to have developed in shallow oceans like stromatolites, eventually the sea algae
would have begun to populate on terrestrial lakes and streams.
B.Diversication (Paleozoic).
The first fossilized plants were found in the late Silurian sedimentary rocks, with small size (may
be 5cm high), very features, no leaves, no branches or true roots, more advanced than
chorophytes that they were derived from. Therefore plants were metazoan (multicellular) and
looked as cooksonia ssp.
Advancement of these plants are the presence of vascular plants.
Reproduction by lot of plants is still through spores. But water as a necessary agent for them to
reproduce can be limitation.
Thereforethose depends on water for reproduction found around swampy areas.
Prothallus is a tiny root like structure lives or found entirely below ground feeding on rotting
substances, is where the sex cell develop.
Male cells develop in the Antheridium and female cells develop in Archigoium.
Botanists prefer to use divisions inseted of phyla. Example in cooksonia ssp, classified as of
division Psilophyla. Most people call them as Psilopsids. Another psilopsids was Rhynia sp,
developed in the middle Devonian. These are evidenced vascular system in plants than cooksonia
sp.
Note: General consensus the psilopsids first developed in the late Sluvian. Before this time the
land mass were largely devoid of all life forms. That is , no vascular plants, no animals and no
insects.
Rain fell, river flowed, the wind blew, glacier advanced and retreated and huricanes and tornados
woured around. But happened over an empty landscape.
The ocean were teaming with life by the time the first vascular plant started to develop on land.

7. It was a far better place to live, but we get to Devonia things are realy going to change in both
the ocean and plants. Hence the Devonian is known as both the age of the fishes and plants.
The major development of plants occurred in the early Devonia (perhaps the late Slurian),
includes the appearance of leaves, to increase the surface area for photosynthesis.
Findings:
 The first leaves were small and located close to stem of the plant.
 Sporangia shifted to the underside of the leaves.
 Plants were getting large. Example, by the middle Devonia, some stood 30m ( 100 feets)
high. This is an advantage of vascular system because get up as long way up from the
ground. Also the taller the trees get the more sunshine.
Therefore, The Devonia is known as the age of plants because of the appearance of a bunch of
new plant division. These divisions includes;
i. Lycopodium sp, examples the club mosses
ii. Sphenopsida. Example, the horsetail which are interesting plants that have joined stem.
iii. Pteropsida (true ferns)
 Have well developed leaves that usually radiates from the stem
 New leaves extends from the top of the stem in a coil roll
iv. Division Pinophyta (gymnosperms)
This consists of 4 major sub divisions or classes
a. Pteridospermophyta(the seed ferns)
Range from devonia to recent.
b. Pinopsida (the conifers)
Range from the misssissipian to recent.
c. Cycadopsida(the cycads)
Range from Triassic to recent
d. Ginkgopsida (the Ginkgos)
Ranges from Jurassic /Cretaceous to recent
All these four (4) classes share one important feature that first appeared during the Devonian
period: Their seeds were considered naked because they were not enclosed in the fruits.
Some seeds seem to be enclosed or encased now days; examples are Peaches, Apples and Grapes
but all these are gymnosperms

8. The seeds ferns look very much like other ferns except that they have seeds on the underside of
their leaf fronds instead of spores.
In contrast the Conifers are very abundant that includes Cedars trees, Spruces trees, and Pines
trees.
One species of Gingko regarded as a longest tree species in the history of Earth, they consists of
male and female Gingko where female is aromatic, thisfemale gingkos is really stink. The only
solution to the smell of it is an axe (to cut off the tree).
During Mesozoic period
There were domination of the seed plants whereby, the cycads, ginkgophyta and glossopteris,
conifers also flourished mostly in Triassic era.
Also gingko and ferns were common in forests during the Jurassic flora whereby the evidence
shows that caytoniaceous seed ferns were another group of important plants during this period
and are said to have been shrub to small tree sized.
During cretaceous flora , which was the important era since the flowering plants known as
angiosperms spread during this period whereby are the common and dominant plant on the earth.
Their evolution was aided by the appearance of bees and birds which developed the symbiotic
relationship between them and the flowers. They also helped in the transport of pollen grains
from one plant to another which facilitated the pollination of plants. Also the evidence shows
that, in the evolution of angiosperms also another major development was the development of
encased seed whereby fruits and nuts are seeds that enclosed within the ovary and in many cases
the ovaries are yummy. This will be explained more.
Evidence for the first Angiosperms
The following are the evidence which shows the different characteristics which separate
flowering plants from other seed plants like gymnosperms, Angiosperms have an ovary enclosed
naturally by carpel or carpels, they have flowers, they have specialized conducting cells in xylem
and phloem, their ovules have double layered seed coat, their pollen have distinctive grain wall
made up of columellae, in their life cycle they undergoes double fertilization where by one sperm
fertilize an egg in which is develop to an embryo, while another sperm fertilize embryo sac
which develop to the endosperm.
Traditionally Angiosperms classified into two major groups that are monocotyledons and
dicotyledons, but recent systematic study there are two monophyletic groups of dicotyledons
recognized which are magnoliids and eudicots. Eudicots with the pollen having three apertures
while magnoliids having a single aperture.
Differences between monocotyledons and dicotyledons
Features Monocotyledons Dicotyledons
Flower parts Have three Have four or five

9. Pollen Have one pore Have three pores
Cotyledon One Two
Primary vascular
bundle in a stem Complex arrangements In a ring
True secondary growth
with vascular cambium Absent Present
Leaf venation Parallel Netlike
FLOWERS PARTS.
The flower parts were divided into two types as that follows
1.Such few features parts like stamens, carpels, number of ovule/seeds per carpel , number of
perianth member and they small (<1 diameter ) possibly unisexual flowers where this flowers are
compared to these of existing angiosperm families as chloranthaceae.
2. They have numerous flowers parts and large bisexual flowers (up to 65mm in diameter) where
by the fossil evidence indicate that the both types of flowers were present at around the same
time. Therefore the number and arrangement of floral organs changed many times during
evolution and that extremes in these features in the earliest angiosperms was not necessary an
expression of distant relationship.
FRUITS
Evidence of fossil angiosperms fruits dates back to the aptian and albian (-121Ma ) with example
from the localities in asia and north America including the fruits of ceretophyllales, juglandels,
and ranunculids where by many of these fruits their seeds were small (1-40mm in length) in
relation to later group in the fossil record a features that is thought to be inductive of the weedy
stature of these early flowering plants so even now there are some fruits that have the small seeds
in side like orange.
LEAVES
Where the distinguish characteristics of leaves include reticulate, venation, forming areoles on
dicotyledon leaves , together with vein that end blind within the areoles and parallal major vein
arranged in the sets of various size and interconnected by smaller veins on the lamina of
monocotyledon.Where in the monocotyledon the leaf is ussualy differentiated int blade and
shealth ,where as in dicotyledon the leaf is usually differentiated into a blade and petiole.where
in the early cretaceous has led to the suggestion that although angiosperms were initialy early
successional plants within a matter of 20 million years they had formed the canopy of late
successional forest.
POLLEN
They have non –saccate ( without the bladder) and in the eudicots has the numerous
symmetrically arranged pores and furrows, where in all angiosperms the pollen wall divided into
an outer layer the (tectum)supported one short ,radial structure which provide an extensive

10. chamber system for the deposition by biologically active substances that acts as recognition
substance on reaching the stigma. In this evidence there were four morphological ear list
angiosperm pollen namely clavitipollenites, pre-afropollis, spinatus and liliacidites
Clavitipollenites, they have possess the characteristics columellae wall with usually one
germination furrows.
Spinatus, with short spines on the margin of the grain.
Pre-afropollis, contain grains that are inaperture (no furrow) but have the grain wall pattern.
Lliacidites, they distinguished due to their single germination furrow and a cell wall composed
of very high columellae.
Nature and distribution of the earliest Angiosperms.
Trees, shrubs or herbs?
Various evidence from the fossil record includes; fossil flowers, fossil records, pollens, leaves
and wood, suggesting that by 100 million years ago (Albian / Cenomanian) there was an
increasing diversity of angiosperms in the flora.
There are three schools of thought.
1. The earliest angiosperms were arborescent shrubs or small trees.
2. The second suggest that, they were herbaceous and rhizomatous in habit such as
chloranthaceae or piperaceae.
3. A third intermediet hypothesis suggested that they were mostly probably herbaceous,
weedy and small shrubs.
Evidence from fossil and molecular records appears to support the third hypothesis.
Angiosperm wood is rare in the early cretaceous fossil record compared with that of gymnasium
wood, and it is not until the late cretaceous that a diverse angiosperm wood flora is apparent.
Most of the specimens of early cretaceous angiosperm wood are also extremely small. It
assumed therefore, this lack of angiosperm fossil wood is a reflection of the herbaceous nature
of the earliest angiosperms.

11. Also the earliest angiosperms seeds tend to be small ( 1 – 40 mm in length) with seed walls and
the small leaves (2 – 4 cm in diameter) with expanded laminae and reticulate venation.
Note: This finding, therefore, support the intermediate hypothesis, that the earliest angiosperms
were herbaceous, weedy and small shrubs.
Dicotyledons and Monocotyledons?
The earliest flower and most of the leaves and pollen appear to the from dicotyledons. Early
monocotyledon fossils are rare.
Suggestions as to why there is the rare early monocotyledons.
i. The majority of monocotyledons were herbaceous and would not have been as well
preserved as the woody dicotyledons.
ii. Similar to the present-day situation, there are many more genera of dicotyledons than
monocotyledons.
iii. Monocotyledons evolved from dicotyledons, and therefore were later evolutionary terms.
Note: Recent estimates; - Based on a phylogeny of monocotyledons angiosperms, suggest that
the major radiation of monocotyledons occurred during the early cretaceous.
Place of Origin and Radiation
Currently, the most favoured hypothesis suggested that;-
 Angiosperms originated in the paleotropics (0 -30), radiating out to colonize higher –
latitude environments some 20 – 30 million years ago.
 The earliest well-dated angiosperm pollen has been found in late Valanginian ( ~ 135 Ma
) fossil localities in Israel and Morocco.
Example.Angiosperms dominated low latitude pollen assemblages, according for 60 – 80 % of
pollen, but in high latitudes, they encounted for only between 30% and 50% floras was made up
of gymnosperms and pteridophytes.

12. WHY ANGIOSPERMS SO LATE TO APPEAR?
Angiosperms were present from as early 140Ma (Berriasian Valangirian)
But in plant evolution terms this late.
The 1st unequivocal evidence for angiosperms in the fossils records is up to 300 million yrs later
than the 1stvascular plants.
Why so late to appear?
Hypothesis,
 Fossils records (the evolved much earlier but went undetected)
 Evolution were triggered by a particular set of environmental conditions
 Biotic interactions Eg. Co-evolution with fauna groups
NATURE OF THE FOSSIL EVIDENCE
Common cited explanation the angiosperms was late due to taphonomy. It suggested that there is
a bias in the fossil records against the preservation of the earliest angiosperms vegetative or
reproductive parts. Therefore angiosperms may have been a part of global vegetation much
earlier than the cretaceous, but were situated in dry up land environments where preservation
potential would have been poor (Axelrod 1952)
Fossil evidence for a pre-Cretaceous origin of angiosperms is based on early examples of
angiosperms such as pollen, fruity axes and leaves.
Angiosperm like pollen, recognized by a restate pollen wall, has found in deposits dating as far
back as the Triassic (220Ma) and includes several species of grains with a single furrow that
have been classified loosely in the Crinopolles group
ENVIRONMENTAL CONSIDERATION
Effects of major environmental changes; including oceanic anoxia, increased tectonic activity
and seafloor spreading that occurring in the mid-cretaceous (140-80Ma)
While there is no clear evidence (as yet) that the diversification and radiation of angiosperms
was triggered by these events, a number of floristic as in mid cretuceous vegetation do correlate
broadly with them. (lupia et al… 1999)

13. It suggested that major environmental changes may have conferred competitive advantages to the
angiosperms at the expense of the previously dominant gymnosperms and pteridophytes
BIOTIC INTERACTION
Dinosaur-angiosperm coevolution
Hypothesis proposal for the late appearance of the angiosperms is that evolution closed
associated with large scale radiation of certain groups of tetra pods, and that of dinosaur feeding
behavior promoted the evolution of flowering plants (bakker, 1978, 1986)
They suggested that changes in herbivore communities fossils from high-low browsers occurred
at approximately the same time as initia levolution and radiation in angiosperms.
Dinosaur fossils evidence suggests that, approximately 160 million years ago in the late of
Jurassic, 95% of the preserved biomass of dinosaurs was made up by of sauropods and
stagesaurs.
Also they suggested that these high browsing forms have put intense pressure on the canopies of
the mature trees, but permitted the development of gymnosperm saplings
Approximately 144 million years ago (Jurassic/ cretaceous boundary), the herbivorous
communities changed considerably and new groups of big, low browsing ornithischian
dinosaurs appeared in the fossil records. Thus the increasing in low browsing dinosaurs led to
increased mortality among the gymnosperm seedlings and thinned out of forest structure, thus
creating gaps in the canopy and high disturbed environment
Early angiosperm such as small structure, rapid life cycle, and high colonizing ability would
have given them the competitive advantage on these disturbed substrates there by promoting the
radiation.
INSECT-ANGEOSPERM COEVOLUTION
Early and mid-cretaceous flowers contained many features to suggest that they were insect
pollinated including stamens with small anther, aid low pollen production, pollen grains often
covered with pollen and it like maternaland they were large than the most effective size for wind
dispersal.
Insect pollination would have been highly advantageous to the early angiosperms, enabling
genetic exchange between widely spaced individuals or small populations.

14. Furthermore, suggesting that self incompatibility mechanisms were present in the early
angiosperms makes process such as insects pollination more critical for cross pollination.
Therefore suggested that the late evolution of angiosperms is closed related to that of insects
evolution.
But fossils evidence of co-evidence of pollination insects with angiosperms is ambiguous.
There is some fossils evidence for insect herbivores on cretaceous angiosperms such as leaf
mines, and other damage to leaf caused by seeding.
EVOLUTIONARY TREND:GYMNOSPERM TO ANGIOSPERM?
Two questions that inevitably arise when discussing angiosperm origin are from which lineage
did they evolve and when and how did divergence of monocotyledons from dicotyledons occurs?
Originally these questions were tackled by examination of only the fossil records, but more
recently techniques including morphological and molecular phylogenic analysis of extinct and
extant groups have allowed the construction of detailed evolutionary relationship between
gymnosperm and angiosperm and monocotyledon and dicotyledon. Later all recent evidence
(morphological and molecular) suggested that angiosperm were derived from a single common
ancestor (they have monophyletic origin). Two of the earliest suggestion for the possible
evolutionary pathway between gymnosperm and angiosperm were via bennettitales and gnetales.
Evidence from bennettitales as the precursor of early angiosperm was based on the fact certain
species of this fossil group had flower like bisexual reproductive organ and similar wood
anatomy. Gnetales are present in fossil records from Grateceous(140 million years ago).
Morphological similarities between species of gnetales and angiosperm, first led to the
suggestion that they were closely in evolutionary term. These include reproductive organs that
are bisexual, presence of vessels, leaves with venation pattern closely approximating to that of
dicotyledons and pollen wall. More recent cladistics analysis which also include the molecular
characteristics of extant species are in argument with the earlier morphological analysis and
demonstrate a close relation between bennettitales, gnetales and the earliest angiosperm. There
are number of hypothesis as to which of the earliest angiosperms from an evolutionary like with
gnatales must suggest that early members of the nyphaeales and prepales were the evolutionary
link between gnetales and angiosperm. Other have suggested a single genus ceratopylum with
the nymphaeles and all members of Laurales. However there is also strong support for woody
Magnoliales. More recent and extensive molecular studies of angiosperm phylogenetics have
however found a number of relationship on their head. Evidence from various cladistic analysis
discribed above have also indicated the relationship between early monocotyledon and
dicotyledon. Again the analysis support the fossil evidence in suggesting that monocotyledon s
were an early branch in angiosperm evolution. However the species or group that forms the
evolutionary link between the monocotyledon and dicotyledon is steel under debate.
BIOGEOGRAPHICAL DISTRIBUTIONOF GLOBAL VEGETATION DURING THE
LATE CRETACEOUS (84-65ma)

15. During the late cretaceous (100-65ma) angiosperm increase in both specious number and
diversity. Angiosperm and shrubs evolve during this time.
Evidence from fossil record suggest number of extant northern and southern hemisphere family
appeared for the first time. These families include ulmacea bethlacea junglandacea and fagacea.
The majority of trees to appear in the late cretaceous have present day distribution that is mainly
tropical or subtropical.
Therefore although many may now be classified as northern or southern temperate species by
their distribution it is probable that they still posses the traits that would enable them to survive
in condition similar to those characteristics of the early environment where they originated.
COOL TEMPERATE BIOMES
The cool temperate biome present day arctic circle comprise Canada Greenland and Siberia in
the northern hemisphere and Antarctica in the southern hemisphere .
The vegetation of cool temperate biome has also reffered to as polar deciduous forest and was
clearly one of the three remaining biome in the late cretaceous not dominated by angiosperm.
Members of pinaceas and taxodiacea were common conifer and the fossil record also include
evidence from modern generation such as pinus .
In southern hermisphere the cool temperature biomes was characterized by abundance
podocarpacean and araucarian conifers and angiosperms.
WARM TEMPERATE BIOME
The warm temperate biome is located between 45 and 65. It encompasses the present day
northern Amerca, sourthern Greenland parts of western Europe Russia and Northern China in the
northern hemisphere Australia and coastal Antarctica in the southern hemisphere
The vegetation characterize this biome include abundant dicotyledons monocotyledons decious
conifer ferns and cycads. Common angiosperm include members fagacea, bethlacea,
junglandacea and ulmacea. Conifer include araucariacea and taxodiacea.
The high diversity of angiosperms dicotyledons in fossil flora from this was thought to
indicate their dominance.
WINTER BIOME
This biome occur between latitude of approximately 30-45 was markedly less diverse than that
of the warm temperate biome and is characterized mainly by the occurance of evergreen
dicotyledons together with both evergreen and deciduous conifer and cycad. A notable feature
of the vegetation of thisregion was relative lower abundance of monocotyledons.
In the southern hermisphere Patagonian flora contained abundant fern and angiosperm families
such as lauracea.

16. The northern limit of the winter biome in northern hemisphere is marked by precence of
evaporative indicating humidit and arid condition respectively.
It is thought therefore that this biome represent transition biome between the arid desert biome
of lower latitude and humidity biomes of higher latitude temperaturideie belts
SUBTROPICAL DESERT BIOMES
Subtropical desert biomes cover north Africa China and Yukatan Penisula west Africa. No fossil
flora have yet been found in these biomes most probably reflecting both low level diversity and
productivity also low preservation potential fossil in arid environment.
TROPICAL SUMMER WET BIOME
It incorporate the margin of present day Africa south America and India from paleo latitude 0-
25. It is characterized by a tropical semi deciduous forest type vegetation .
Common element in the vegetation of this region include dicotyledon and monocotyledon
ferns, conifer and cycads.Evidence from fossils pollen and wood sugest that common conifer
include members of the araucariacea and podocarpacea.
The combined evidence from fossils flora composition leaf physiognomy and sedimentological
indicator suggest that this region was characterized by hot sub humid to semi arid climate
typical of present day summer wet or savanna region.
TROPICAL EVERWET WET BIOMES
It covers west Africa Malysia, Somalia, and Colombia. During late cretaceous period equatorial
region was dominated by species of arecacea other angiosperm present include protocea and
other dicotyledons groups.
Fern tree were also abundant . A striking feature of this biome is almost completely absence of
evidence for either evergreen or deciduous conifer with exception of araucaricea.
It is noted that the feature common both upper cabornferous and present days are the precence
of polar ice caps high latitude temperature gradient and comperatively low atmosphere
concentration.
CONCLUSION
From the above discussion it seem that there is advancement of plant species from one era to
another for instance vascular system in plants like Rhynia sp than Cooksonia sp in the middle
Devonian. Also the appearance of leaves for photosynthesis which were small and located close
to the stem of plant in late Devonian.Also it shows that angiosperms were the first to emerge

17. although they late evolved because their evolution were triggered by a particular set of
environmental condition hence remained undetected earlier.
REFERENCE
Taylor T.N &Taylor .L The Biology and Evolution of fossil plants (Prentice Hall, New Jersey
1993)
Gray, J & Shear, W. Early life on land(1992)
Niklas K.J Plant allometry. The sculing of form and process( Univ.Chicago Press 1994)