Transcript Plant Groups

Plant Groups
• In order to begin to classify plants,
consider the structure by which the plant
absorbs water.
• Plants are either vascular or non-vascular.
Vascular plants have tube-like structures
that transport water from the roots to the
stem to the leaves.
• Non-vascular plants absorb water only
through their surfaces.
Non –Vascular Plants
• Non-vascular plants are plants that lack
water-conducting vessels in their tissue
known as tracheids.
• Tracheids are located in the xylem, along
with wood vessels.
• They are the most important waterconducting vessels in seedless vascular
plants and in gymnosperms.
Bryophytes
• Bryophytes do not have a true vascular system and are
unable to pull water and nutrients up from the ground at any
significant distance.
• Lacking this specialized system distinguishes bryophytes
from ferns and flowering plants. It is for this reason that they
are considered to be rather primitive plants.
• They are regarded as bridge between water plants like algae
and higher land plants like trees.
• They are extremely dependent upon water for their survival
and reproduction and are usually found in moist areas like
steams and forest floors.
• They first evolved about 500 million years ago and were
likely the earliest land plants.
• The lack of vascular tissue limits their size, generally
keeping them under 12 centimeters high. Roots are absent
in bryophytes, rather there are root-like structures known as
rhizoids.
Bryophytes (cont’d)
• The word bryophyte refers to a group of plants that
includes the mosses, liverworts, and hornworts. There
are about 25,000 different species.
• Although small in size, they are one of the largest
groups of land plants and can be found almost
everywhere in the world.
• There are more species of bryophytes than the total
number of conifer and fern species combined.
• A common example of the Bryophytes are Mosses.
• Aside from lacking a vascular system, they have a
gametophyte-dominant life cycle, i.e. the plant's cells are
haploid for most of its life cycle.
• Sporophytes (i.e. the diploid body) are short-lived and
dependent on the gametophyte.
Bryophytes (cont’d)
• These plants do not flower and as a result never produce
seeds.
• They reproduce by spore production
• The process by which they produce spores is termed
alternation of generations.
• Liverworts and mosses have been found in the fossil
record dating as far back as 300 million years ago - the
Paleozoic era. As a result of an incomplete fossil record
they are believed to have shared a common ancestry
with the green algae.
• Bryophytes have very distinct characteristics that has
allowed for the development of three distinct classes the Hepaticae (liverworts), Anthocerotae (hornworts),
and Musci (mosses).
Tracheophytes (Vascular Plants)
• The vascular plants have specialized
transporting cells xylem (for transporting water
and mineral nutrients) and phloem (for
transporting sugars from leaves to the rest of the
plant).
• When we think of plants we invariably picture
vascular plants.
• Vascular plants tend to be larger and more
complex than bryophytes, and have a life cycle
where the sporophyte is more prominent than
the gametophyte
Major evolutionary advances of the vascular plants.
Advance
Development of the rootstem-leaf vascular system
Reduction in the size of the
gametophyte generation
Development of seeds in
some vascular plants
Spores/Pollen
Green Algae
nonvascularized body
(thallus) that may be
variously shaped,no leaves,
shoots, or roots
wide range of life cycles,
some gametophyte
dominant, others sporophyte
dominant
no seeds
spores for resisting
environmental degradation
Bryophytes
Tracheophytes
no vascular system,leaflike
structures are present, but
lack any vascular tissue
early vascular plants are
naked, rootless
vascularized stems,later
vascular plants develop
vascularized leaves, then
roots
sporophyte generation
dependant on gametophyte
generation for food;
gametophyte is free-living
and photosynthetic
progressive reduction in size
and complexity of the
gametophyte generation,
leading to its complete
dependence on the
sporophyte for food ,in
angiosperms, 3 celled male
gametophyte and a (usually)
8 celled female gametophyte
no seeds
seed plants retain the female
gametophyte on the
sporophyte
Spores that germinate into
the gametophyte generation
Spores that germinate into
the gametophyte generation
or spores that have the
gametophyte generation
develop within themselves
Ferns
• Ferns are a very ancient family of plants: early fern
fossils have been found before the beginning of the
Mesozoic era, 360 million years ago.
• They were thriving two hundred million years before the
flowering plants evolved.
• As we know them now, most ferns are leafy plants that
grow in moist areas under forest canopy.
• They are "vascular plants" with well-developed internal
vein structures that encourage the flow of water and
nutrients.
• Unlike other vascular plants, where the adult plant
grows from the seed, ferns reproduce from spores and
an intermediate plant stage called a gametophyte.
Ferns (cont’d)
• There are two main differences between the
ferms and other vascular plants.
• The first is that ferns are delicate plants that will
only grow in areas which are moist.
• They prefer sheltered areas on the forest floor,
near streams and other sources of permanent
moisture.
• They cannot grow in hot dry areas like flowering
plants and conifers.
• They do no have structures to prevent
dessication - drying out.
Ferns (cont’d)
• The second is linked to the first: ferns reproduce
differently from the conifers and flowering plants.
• It all has to do with moisture. Not just the moisture that
allows the plant to live where it does, but the moisture
that allows it to reproduce there. They have a more
complicated method that depends on there being liquid
water for the process to complete.
• The sperm cell (male gamete nust "swim" to the egg).
• As a result, they can only reproduce where there is
sufficient moisture: reproduction requires moisture.
• Higher plants have a very "tough" reproductive
system: the pollen from the male flower is very
resilient, and the female flower nurtures the
seed until it is ready to grow.
• The seeds themselves are able, because of their
structure, to wait for long periods in adverse
conditions before they grow.
• So the higher vascular plants have evolved to
occupy nearly every place on the land surface of
the earth.
Seed Plants
• The seed plants are divided into two groups too.
These groups are the gymnosperms and the
angiosperms.
• Gymnosperms are plants which produce seeds
in cones.
• One well-known type of gymnosperm is the
conifer, which includes pine, fir and spruce trees.
• In this province the Gymnoserms are our
dominant vegetation.
• Angiosperms are plants which make their seeds
in flowers thus we call angiosperms flowering
plants.
• Gymnosperms have seeds but no fruits or flowers.
Gymnos means naked, sperm means seed: in other
words gymnosperm equates to "naked seeds".
• Gymnosperms developed during the Paleozoic Era and
became dominant during the early Mesozoic Era.
• There are over 700 living species that are placed into
four divisions. These being:
• Conifers,
• Cycads,
• Ginkgos, and
• Gnetales
• The largest, most widespread, and most familiar group
are the conifers, Division Coniferophyta, that has about
550 species in 50 genera. T
• hey include many familiar trees such as Douglas firs,
Black Spruce and White Spruce.
• The other three Divisions of gymnosperms are much
smaller and rather obscure.
• Division Cycadophyta contains about 140 species of
mainly tropical palm-like plants called cycads.
• Division Ginkgophyta contains but one species, an 80
million-year-old evolutionary leftover known as the
maidenhair tree.
• Finally, Division Gnetophyta contains about 70 species,
some with some very odd characteristics.
Cycads
Cycads retain some fern-like features,
notably their leaf shape.
Cycads were much more prominent in the
forests of the Mesozoic than they are
today.
Presently, they are restricted to the tropics.
Ginkgos
The ginkgos were also a much more prominent group in
the past than they are today.
The sole survivor of this once hardy and varied group is
Ginkgo biloba, the maidenhair tree.
Extensively used as an ornamental plant, Ginkgo was
thought extinct in the wild until it was discovered growing
natively in a remote area of China.
Ginkos have separate male and female plants. The
males are more commonly planted since the females
produce seeds that have a harsh odor.
Pollination is by wind.
Recently, Ginkgo has become the current herbal rave.
Conifers
The conifers remain the major group of
gymnosperms.
In this province and other regions of the
world which possess similar climates and
soil they are the dominant tree type.
Their needle shaped leaves and other
structures allow for survival in this type of
environment.
•
Angiosperms
The angiosperms, were the last of the seed plant groups to evolve,
and appeared over 140 million years ago during the later part of the
of the Age of Dinosaurs.
All Angiosperms produce flowers.
Within the female parts of the flower angiosperms produce a diploid
zygote and triploid endosperm.
Fertilization is accomplished by a variety of pollinators, including
wind, animals, and water.
Two sperm are released into the female gametophyte: one fuses
with the egg to produce the zygote, the other helps form the nutritive
tissue known as endosperm.
• The angiosperms produce modified leaves that are grouped into
flowers that in turn develop fruits and seeds.
• There are approximately 230,000 known species. Most
have larger xylem cells known as vessels that improve
the efficiency of their vascular systems.
• The classical view of flowering plant evolution suggests
they developed from evergreen trees that produced
large Magnolia-like flowers.
• Recent Fossil evidence though appears to contradict this
notion and a debate among botanists has ensued.
• Regardless of their origin though it is agreed that the
angiosperms underwent a significant adaptive radiation
during the Cretaceous, and for the most part escaped
the major extinctions that occurred at the end of the
period