Plant Classification,
Function, and Structure
Introduction




Plants are complex organisms that consist of tissues and cells
Plants consist of leaves, stems, roots, and flowers
Understanding plant growth and the function of plants is very
important in horticulture
Horticulturists apply their knowledge of plant anatomy of the
different plant organs to promote growth and high quality
crops
Objectives
Explain why it is important to classify plants
1.

•
•
2.
3.
Explain different ways plants are classified according to
their taxonomy, and use scientific naming
Explain the hierarchal classification system
Use a dicotymous key to classify organisms
Describe the differences among annuals, biennials,
and perennials
Explain the processes of photosynthesis and
respiration
Objectives (Learning Goals)
4. Identify and describe the functions of the vegetative plant parts
a. Leaves
Identify and describe the parts the functions of the internal and external
leaf structures
Discuss the differences between simple and compound leaves, and
identify types of compound leaves and their arrangement on a stem
b. Stems
Identify and describe the parts and functions functions of the internal and
external stem structures
c. Roots
Identify and describe the parts and functions of the internal and external
root structures
Describe the differences between taproot, fibrous, and adventitious root
systems
5. Identify and describe the parts and functions of
reproductive plant parts
Explain the difference between complete and
incomplete flowers
Identify types of flower inflorescences
6. Explain the economic importance of all plant parts
7. Describe the structural differences between monocots
and dicots
Plant Classification
Explain why it is important to classify plants
Explain different ways plants are classified
1.
2.
•
•
•
3.
Explain and use Scientific Plant Classification
and Naming
Explain the hierarchal classification system
Use a dicotymous key
Describe the differences among annuals,
biennials, and perennials
Why Classify Organisms?

Classification systems improve:




our ability to explain relationships among things
aid our memory
aid our prediction
provide unique, universally used names for
organisms
Classifying Plants


Scientists use the similarities of plants to
classify them into groups.
There are different classification systems
based on





Stem Type
Foliage Retention
Life Cycle
Use
Scientific classification

Stem Type Classification


Herbaceous Plants – have
stems that are soft and not
woody (herbs, vines,
turfgrasses) that die back to
the ground each year
Woody Plants- shrubs, trees,
or certain vines which
produce wood and have buds
surviving above ground over
winter

Foliage Retention


Deciduous Plantsleafless during portion of
the year (winter)
Evergreen- keep leaves
year round


Narrow leaf (needle like
leaves) evergreens
Broadleaf (flattened leaf
blade) evergreens

Life Cycle –



Vegetative phase: part of life when a plant seed germinates
and grows producing leaves, stems and roots.
reproductive phase: plant flowers and produces fruit
senescence or dormancy phase: inactive or slow plant
growth



Annuals – complete life cycle in less than one year
Biennials – complete their life cycle in two years
Perennials – herbaceous or woody plants that grow indefinitely
from year to year

Annuals- flowering, then
production of seed is a sign
of death


Dead-heading: the removal of
flowers and seeds to continue
life and bloom for longer
periods of time
Annuals are often divided
into groups based on what
season or climate is best for
growth

Biennials


During first season of
growth the plants grow
vegetatively then become
dormant in winter
The following spring the
plants produce flowers
and fruit then die.

Perennials: plants that
live for more than two
seasons


Above ground portions
of perennials generally
die in winter but grow
new shoots and leaves
the following spring
from the below-ground
portions of the plant
Can be deciduous or
evergreen

Hardiness


Tender plant: unable to
survive extreme climate
and temperature
Hardy plant: able to
withstand colder
temperatures

Use




Edible
Ornamental
Medicinal
Back in the day:


Poisonous
safe
Scientific Naming


Avoid confusion concerning the names of
plants.
Scientific names of plants are expressed in
Latin because it is a international language and
was used by early scholars to express plant
names

Scientific Classification


Based on morphology of plants (form and structure)
Botanical Nomenclature: scientific classification of plants


Includes Genus, Species, Variety, Cultivar
Scientific Name:




written in Latin
First letter is always capitalized and the species is lower case
Plants in same genus have similar characteristics
Variety or cultivar: given to plants of the same species that have a
sufficiently different appearance
Latin names of plants are
italicized:


Because it is conventional to italicize words
and phrases that are expressed in a different
language.
Example - The most commonly known
cultivars of Acer rubrum ( red maple) are “Red
Sunset” and “Autumn Flame,” which are the
most reliable for brilliant reds and a longlasting display of foliage.
The generic name of the
plant is:

Placed first and begins with a large letter.

Examples: Acer-(maple), Papaver-(poppy),
Pinus-(pine)

When classifying plants, it is important to first
understand that the more they are categorized
the more specific the plant categories are.
Classification begins with Kingdom and
continues with Phylum, Classes, Orders,
Families, Genera, and Species. Each of these
can be further subdivided.
A genus can be defined as:

A group of plants that have more in common
with each other than they have with the
members of any other genus.
A species can be defined as:


A group of plants that are alike in almost every
feature and consistently produce like plants.
Example - Betus lutea is yellow birch (lutea
means “yellow”)
TAXONOMIST

A person who identifies and classifies plants!
Kingdom Plantae


Plants dominate the land and many bodies of
water. Plants exhibit tremendous diversity.
Some plants are less than .04 inches in width,
and some plants grow to more than 328 ft in
height.
All organisms in this kingdom are
multicellular and most are photosynthetic and
live on land.


The first true plant is thought to have been
similar to a green alga, with adaptations that
enabled it to survive the dry conditions of land.
From that algal ancestor, a wide variety of
plants have evolved.
Phylum Bryophyta

Know as mosses:




More than 10,000 species
No vascular tissue
Seedless, reproduce with
spores
Sphagnum moss is a genus
of moss that is a major
component of peat bogs
and has a high water
holding ability, making
very useful to the world of
horticulture
Phylum Hepatophyta

Know as liverworts



6,500 species
Unusual looking plants
that grow in moist shady
areas
Non-vascular
Phylum Anthoceroophyta

Known as Hornwarts




100 species
Nonvascular
Resemble liverwarts
They share an unusual
characteristic with algae;
each cell usually has a
single large chloroplast
rather than numerous
small ones
Phylum Psilotophyta

Known as whisk ferns




10-13 species
Vascular, seedless
Not actually ferns, have
no leaves or roots
Epiphytes- grow on other
plants but not considered
parasites
Phylum Lycophyta

Club Mosses





1,000 species
Vascular seedless
Look like miniature pine
trees
Bear spores and have
roots
Many are endangered
species
Phylum Sphenophyta

Horsetails





15 species
Vascular seedless
Jointed stems
Outer cells contain silica,
the major component of
sand
Often used by american
pioneers to scour pots
and pans
Phylum Pterophyta

Ferns





12,000 species
Vascular, seedless
Beautiful and feathery
leaves
Most have an
underground stem
Most produce spores on
the underside of their
leaves
Phylum Cycadophyta

Cycads






Gymnosperms
Vascular with seeds
100 species
Most lived in age of
dinosaurs
Now mostly ornamental
Look fernlike
Phylum Ginkgophyta

Ginkgo





Gymnosperms
Vascular with seeds
1 species
Also flourished in age of
dinosaurs
Ginkgo biloba is only
remaining species native
to China
Phylum Coniferophyta

Conifers





550 species
Gymnosperms
Vascular with seeds
Important sources of
wood, paper, turpentine,
resin, ornamental plants
(used in horticulture)
Gin flavored with juniper
seeds
Phylum Gnetophyta

Gnenophytes





Gymnosperms
Vascular with seeds
70 species
Odd cone bearing plants
Ephedra is a species that
produces the drug
ephedrine used for
weight loss
Phylum Anthophyta

Flowering Plants




Vascular with seeds
Produce flowers for
reproduction
240,000 species, largest
phylum
Monocots vs. Dicots
Parts of the Plant and
Their Functions
Chapter 4
Introduction


Plants are living organisms that
have complex chemical processes
that direct growth and
development
They have four main body parts
where these processes take place.




Leaves
Stems
Roots
Flowers
Plant Parts
Plant Parts

Vegetative


Leaves, stems, roots
Reproductive

Flowers
Leaves



The food factory of the
plant, producing all food
that is used by the plant and
stored for later use by the
plant or by animals
Leaves are the most obvious
and more diverse structures
of plants and leaves
Vary in shape and size as
well as arrangement around
the stem, this helps in plant
classification
Leaf Functions



Make food for plant (photosynthesis)
Food/energy storage
Gas Exchange



Water vapor
Carbon dioxide
Oxygen
External Leaf Structure





Petiole= leaf stalk, stem
Blade= a larger, usually the
flat part of the leaf used to
collect light
Midrib= large center vein w/
extensions
Veins= extensions of midrib
that give leaves their form
and move water, minerals
and nutrients
Margin= edge of leaf, varies
and aids in plant
classification




Leaf apex: tip of leaf
(round, pointed,
indented, etc.)
Leaf base: place where
blade attaches to petiole
Leaf covering: may be
waxy or hairy
Stomata: tiny pores
through which gases
and vapor pass in or out
of leaf
Leaf Venation Pattern

Parallel Venation


Veins are parallel to the
midrib and nearly equal
in size and extend length
of leaf
Grasses, tulips, daffodils

Pinnate Venation

Midrib with smaller,
lateral veins branching
from it

Palmate Venation

Leafs have three or more
major veins that extend
from the base of the leaf
blade. Smaller veins
branch from these main
branches
Monocot vs Dicot Leaf Venation

Arrangement of veins in
a leaf


Monocots, like grasses
have parallel venation,
meaning veins are
roughly parallel to each
other
Dicots have pinnate or
palmate net venation,
meaning that the main
vein or veins repeatedly
branch to form a
conspicuous network of
smaller veins
Types of Leaves

Simple Leaf


Consists of a single leaf
blade and a petiole
Compound Leaf

Made of a petiole and
two or more leaf blades
called leaflets
NOTE


To determine type of leaf, one must first look
for the position of the axillary bud located at
the base of the entire leaf
Leaflets of compound leaves do not axillary
buds

Compound leaves may be:



Palmately Compound: leaflets come from a point
at the tip of the petiole
Odd Pinnate: leaflets arranged along both sides of
the petiole with a leaflet occurring on the end of
the petiole
Even Pinnate leaflets arranged along both sides of
the petiole without a leaflet occurring on the end of
the petiole
Leaf Arrangement on Stems

Leaves are attached to stems in patterns that
can aid in plant ID



Opposite: leaves and buds are directly across from
one another
Alternate: leaves and buds are alternated or
staggered along the stem
Whorled: three or more leaves and buds arise from
the same point on the stem
Modified Leaves



Bracts: leaves located
just below the flower
Tendrils: extensions that
allow plants to climb
Some thorns
Internal Leaf Structure

Internally, leaves have specialized cells which
perform very important tasks.


Epidermis- skin of plant, single layer of cells that protect
plant from loosing moisture
Guard Cells- cells that open and close a small space or
pore, known as stoma, on the under side of the leaf. They
allow the plant to transpire, or give off moisture and
exchange gases such as oxygen and carbon dioxide. Guard
cells are crescent shaped and as the cell walls become
turgid, due to water pressure in the cells, they open the
stoma.


Mesophyll- a ground tissue composed of
chloroplast-rich parenchyma cells (loosely
packed, cube-shaped cells with thin flexible
walls)
Chloroplasts- cells that make food


The green color of the chloroplasts, which gives
green leaves their color, comes from the
chlorophyll they contain.
These cells, through a process called
photosynthesis, manufacture food.


Palisade mesophyll- a layer of cells that occur
directly beneath the upper epidermis and is the
site of the most photosynthesis
Spongy mesophyll- irregularly shaped cells
surrouinded by large air spaces, which allow
oxygen, carbon dioxide, and water to diffuse
into and out of the leaf
Leaf Cross Section
Photosynthesis

The process by which Carbon dioxide and
water in the presence of light are converted to
sugar and oxygen
It is the process that creates the beginning of
the food chain for all living things on earth
6 CO2 + 6 H2O + 672 kcal = C6H12O6 + 6O2

Carbon Dioxode +

Watch and Learn


Water
+ light energy
=
Sugar
+
oxygen
Respiration




Plants respire 24 hours a day just like animals
do
They consume oxygen and give off carbon
dioxide
All parts of plants must have adequate access
to oxygen in order to survive
Plants produce more oxygen than they
consume
Dicot Leaf Cross Section
Monocot Leaf Cross Section
Dicot Epidermis
Monocot Epidermis
Stems

Functions:




Movement of materials, such
as the movement of water and
minerals from roots upward to
the leaves and movement of
manufactured food from the
leaves down to the roots
Support of leaves and
reproductive structures
Sometimes used for storage
(Irish Potato)
Green stems also manufacture
food just as the leaves do
External Stem Structure




Leaf Scar: Heart-shaped scar on twig
where last years leaf grew.
Node: Growth region on stem. Region
around bud or leaf stem.
Internode: segments of stems, between
nodes
Bundle Scar: Tiny bumps in leaf scar
where veins enter the leaf from the
stem.


Bud: part of plant capable of developing into a
new shoot, contains apical meristem tissue and
is enclosed by specialized leaves called bud
scales
Lenticels: tiny pores located on the stem that
allow for gas exchange between the plant and
the environment. Some plants, like cherry
trees, have conspicuous lenticels



Terminal Bud: Bud on end of a branch,
where all of next years length (of branch) is
added.
Lateral (axillary) Bud: Small buds along
length of branch that develop into leaves,
lateral branches, or flowers.
Apical Dominance: The terminal bud
dominates all other lateral buds by giving
off hormones. If the terminal bud is cut off,
the lateral buds will grow longer.
Internal Stem Structure

Stems are composed of three tissue types

Epidermal tissue-Stems are encased by a
transparent epidermis which is usually about one
cell thick and which often has trichomes. The
trichomes serve various purposes; some plants
secrete juices to attract insects, which others have
sharp trichomes which often entangle the insects
and keep them from feeding while they struggle to
free themselves.

Vascular Tissue: tissues that serve as a
transport system within a plant and act
like straws
Xylem: responsible for the movement of
water and nutrients from the roots of a plant
to the stems, leaves, and reproductive organs
 Phloem: responsible for transporting sugars
made by photosynthesis from leaves to
stem, roots, and reproductive organs where
they will be used for growth, repair, and
reproduction


Ground tissue-Between the epidermis and the ring
of vascular tissue in dicots is the cortex. Most cells
of the cortex are parenchyma. Cortical cells are
photosynthetic in plants and often store starch. In
dicots, the ground tissue with the parenchyma
cells in the center of the stem is specialized for
storage and is called pith. Pith cells are often
lignified, arranged loosely, and the pith may
contain secretory structures such as laticifers.
Because monocots have vascular bundles
throughout their ground tissue, their stems do not
have a discernible pith; the parenchyma cells in
monocot stems are referred to simply as ground
tissue
Specialized or Modified Stems





Specialized stems serve as underground food and
water storage
Bulbs: short flattened stems that bear fleshy food
storage leaves. At the base of each fleshy leaf there is
a bud (onion, lily, tulip, narcissus)
Corms: look like bulbs but are more globe shaped
(crocuses and gladioluses)
Rhizome: underground horizontal stem (iris, calla
lily, ferns) stem tubers are swollen tips of a rhizomes
Stolon (runner): grows horizontally above ground,
produce roots at tip or nodes
Economic Importance of Stems


The stems of some
plants, such as the Irish
potato and asparagus,
are used as food.
Others are used as
building materials, such
as the lumber from tree
trunks
Roots

Roots are underground and therefore, are not
easily visible and are often forgot about. Roots
function to:




Anchor the plant and hold it upright
Absorb water and minerals from the soil and
conduct them to the stem
Store large quantities of plant food
Propagate or reproduce some plants
Types of Roots

Taproot: a system of
roots that has longer and
fewer roots


Can reach lower water
supplies and have large
food holding capacity
Roots may be lost or cut
off when dug up
Types of Roots

Fibrous Roots: a system
with shorter, smaller,
and more compact roots


More prone to drying
Easier to dig up and
transplant
Types of Roots

Adventitious Roots:
specialized roots that
grow from stems and
leaves




Can prop up plants
Some absorb water and
nutrients from the air
Some used in vegetative
reproduction
Help plants climb walls
(ivy and other vines)
Root Structure
Internal Root Structure

Similar to that of
the stem.

Made of phloem
and xylem
External Root Structure

Primary Root:



First structure to emerge
from a germinating seed
that immediately absorbs
water and minerals for
growth.
Grows and branches out
Secondary Roots

Extensions of the
primary root
External Root Structure

Root Cap: protection for root tip.


It produces a slimy substance that
functions as lubricating oil, allowing
the root to move more easily through
the soil as it grows.
Root Hairs: extensions of roots

Increase surface area and plants ability
to absorb water
Watch Me
And Me Too
FLOWERS-Fruits-Seeds
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Introduction



To people, flowers are something
beautiful that symbolize many
feelings such as love, happiness,
and sorrow
To the plant, they are the means of
reproducing and ensuring their
survival
Flowers are considered to be a
highly specialized branches and
parts of flowers to be leaves
Flower Parts


Receptacle: swollen tip
of the branch where all
parts of flower stem
from
Sepals: outermost whorl
on flower that surrounds
and protects the other
parts of flower before it
opens as it is developing
Flower Parts

Petals: 2nd whorl on flower generally used by
plants to attract insects for pollination
Male Plant Parts

Stamen: collective name for male parts


Anther: contains microsporangia, which produce
microspores that develop into pollen grains
Filament: supports the anther
Female Plant Parts

Pistil: collective name for
female sex organs which are:



Ovary: enlarged base of pistil;
contains ovules which develop
into seeds once fertilized
Style: stalk-like part of pistil
leading from ovary to:
Stigma:sticky or hairy part of
pistil that is capable of catching
pollen grains
Types of Flowers

Complete:

Contains both male and
female parts within the
same flower

Incomplete

Contains male or female
parts, but not both
Flower Inflorescences

To help identify the plants, flower
forms are grouped as to their
position or arrangement on a
stem.
 Solitary Flowers: one flower
on a stem
 Inflorescence: arrangement of
flowers on a stem
Inflorescence Types

Cyme:



Takes on several forms
Usually flat topped
Baby’s breath

Spike



Elongated inflorescence with
a central axis along which are
sessile flowers
Sessile flowers are attached
directly without a stem or
stalk
gladiolus

Raceme
 Elongated inflorescence with
a central axis along which are
simple pedicels of more or
less equal length
 Snap dragons, delphiniums,
Scotch broom, and stalk

Panicle


Elongated inflorescence
with a central axis along
which there are branches
that are themselves
branched
Astilbe, begonias

Corymb


Flat topped inflorescence
having a main vertical
axis and branches of
equal length
yarrow

Umbel


Inflorescence having
several branches arising
from a common point
Queen Anne’s lace,
amaryllis

Spadix


Spike with a thickened,
fleshy axis, usually
enveloped by a showy
bract called a spathe
Calla lily, anthurium

Catkin


Spike, raceme, or cyme
composed of unisexual
flowers without petals
and falling as a unit
Willows, alders, birch
Pollination



Pollination occurs when pollen grains are transferred from the
anther to the stigma
Pollen grains then germinate and a pollen tube grows down the
style until it reaches the ovules in the ovary
Fertilization occurs when one sperm nucleus fuses with the
egg cell nucleus, forming a zygote that will become a seed

The other sperm nucleus fuses with two nuclei in the ovule to create the
endosperm
Cross Pollination

Controlled cross-pollination is an important technique
used by plant breeders in developing new cultivars



Occurs when pollen grains from the flowers on one plant
transfer to the stigmas of flowers of another plant
Occurs between closely related plants
Hybrids: offspring resulting from cross-pollinating two
different varieties of a species

Done to improve traits or characteristics
Seeds

Mature, fertilized
ovules, or eggs, that are
contained in a fruit




Range in size from a few
millimeters to several
centimeters
Can be flat, cylinder
shaped, or rounded
Distributed my animals,
wind, fire, etc.
All viable (living