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Demystifying
Plants:Botany for
Gardeners
Plants in our Ecosystem
• Capture sun’s energy
• Food source
• Replenish atmospheric oxygen
• Participate in water cycle
• Moderate world climate
• Provide shelter
• Source of numerous raw materials
• Support a myriad of other living things
When scientists study plants,
what do they study?
• The way plants grow and function (plant
morphology and physiology)
• The way plants are genetically related to each
other (plant taxonomy)
• How plants interact with their natural
environment (plant ecology)
• How plants evolve and adapt to the environment
at a gene and molecular level (plant genetics)
Horticulture = Botany applied
• Identify plants
• Grow & propagate plants
• Influence flowering & fruit
production
• Control unwanted growth
• Maintain plant health
• Modify plant features through
breeding and selection
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Horticulture is the study of
useful plant oddities
In disturbed, reorganized, and
coddled landscapes
Variegated Norway maple
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Plants don’t live in isolation
• Physical environment
(soils, climate,
moisture, etc.)
• The living
environment (other
plants, people,
animals, insects,
fungi, etc.)
Plant communities are always
changing
• This is called plant
succession
• Examples from
native landscapes
• Examples from
gardening
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Horticultural plant classifications
• Sun or shade
• Acid or neutral or alkaline soils
• Drainage preference
• Growth habit (woody vs. herbaceous; tree
vs. shrub; evergreen vs. deciduous; etc.)
• Cold hardiness
• Reproductive strategy: annual, biennial,
perennial.
• Plant family
How do plants get through
winter?
Climate zones define the average low winter temperatures for large areas.
Your property may be in a micro-climate that differs (either warmer or colder) from the general cold winter pattern for your region.
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The importance of life cycles
• Annuals– winter
– summer
• Biennials
• Perennials
– Herbaceous
– Woody
• deciduous
• evergreen
Winter annuals
• Spread exclusively by
seeds that germinate in
the fall/winter and go to
seed in the spring to early
summer and die.
• Some, in this climate, grow
year round
• Examples: chickweed,
groundsel, red dead
nettle Groundsel – Senecio vulgaris
Summer annuals
• Also spread by seed
that germinate in the
spring and summer
• Flower and seed by
fall and die
• Compete with
vegetable crops
• Examples: pigweed,
lambsquarter, and… Purslane
Biennials
• Spread by seed that
germinate in spring-fall
• Overwinter as a
“rosette”
• Flower and seed next
year in the late spring-
summer and die
Bull thistle – Cirsium vulgare
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Herbaceous perennials
• Tops die back
• New shoots each
spring from
roots/crown
• Spread by seed
and vegetative
pieces and don’t
die
Hedge bindweed Calystegia sepium
aka Morning glory
Woody perennials• Tend to spread by
seeds.
• Some vegetative
spread with some
species e.g. ivy,
& root suckers on
some trees. We
propagate by seed,
cuttings, grafting, etc
• Don’t die
Classifying plants into families
• Why do we care?
• What are the key
botanical characteristics
used? Why?
Why flowers?
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Linnean classification of plants
• Lower vs. higher plants
• Gymnosperms (conifers
and others) and
Angiosperms
• Monocots and dicots
• Family: Aceracea
• Genus: Acer
• Species: rubrum
• Cultivar: Autumn Blaze
Summary of differences, monocots & dicots
Chloroplasts capture light energy
CO2 + H20 + light energy = sugars + O2
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What are the requirements for
plant growth?Light energy
Heat (some)
Stored energy
Water
Carbon, hydrogen, oxygen
Mineral elements
A few other important concepts
• Meristems
• Plant
hormones
Meristems
• Areas of actively
dividing cells
that develop into
plant tissues
and organs
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Plant hormones aka plant growth
regulatorsChemicals present in
tiny quantities that
affect plant
development and
response to
environment including
dormancy, growth rate,
fruit, flowering, etc.
Plants have to start from
something
Dr. B. Rathinasabapathi - U. Florida
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Seed Anatomy
• Embryo - miniature plant in an arrested state of development
• Endosperm - food supply (can be comprised of proteins, carbohydrates, fats)
• Seed coat - hard outer covering that protects from disease and insects; also repels water
• Temperate seeds measure winter temperatures
Cut away seed
• Seed is a dicot with
two seed leaves
• Root apex at lower
left
• Root connected to
hypocotyl where
cotyledons are
attached
• Seed coat
• Endospeerm
Seeds and Seedlings Seed germination requirements
• Activation of embryo
within seed
• Preceded by water
penetrating seed coat
• Oxygen, favorable
temperature cycle, and
(in some species) light
required
• Other cues
.
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Other germination factorsDicot
Monocot
Cotyledons = modified leaves
beandicot seed = 2 cotyledons
monocot seed = 1 cotyledon
cotyledons
first true leaves
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Vascular system (“plumbing”)
Root functions
• Anchors the plant
• Absorbs water and
minerals
• Stores food
• Reproductive organ
• Compete with other
plants for water and
minerals
Root Structure
Lateral Root
Primary Root
Root Hairs
Root Tip
Root Cap Meristematic Zone
Zone of Elongation
Zone of
Maturation
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Meristematic Zone
Root Cap
Root Tip
Zone of Elongation
Photo: Source Unknown
Tap Root Fibrous Root
Dicots
Monocot
Modified roots
Tuberous root – sweet potato Storage root of beet
Tuberous root, dahlia Storage root – carrot
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Root Anatomy
Epidermis
Cortex
Endodermis
Xylem
Phloem
Photo: Botany for Gardeners, Capon
What’s inside a root?
buttercup
The vascular system is in the center
What’s inside a root?
buttercup
xylemcortex
phloem
cambium in woody roots
Root Tissues
• Xylem - conduct water & nutrients
• Phloem - carry sugars & starches
• Endodermis - contain vascular tissues
• Cortex - primary tissue surrounding vascular bundle
• Epidermis - outermost layer of plant tissues, protective layer
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Unique to roots!
root cap -located at root tip & protects growing point
Origin of lateral roots
Notice the root cap on the lateral root –cut away section
Root hairs on a radish seedling
Root hairs absorb most of the water a plant gets –very tiny
Root hair cross-section
• delicate
• thin-walled
• room for lots of water
• has lower water pressure than the outside soil
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Let’s review Mycorrhizae = fungal partners
on/in higher plant roots
Mycorrhizal fungus
Which partner gets what?
How much water do these plants move?
Corn Big leaf maple
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Factors influencing root growth
• Light captured
• Gravity
• Temperature
• Soil texture
• Oxygen
• Moisture
• Minerals
• Salt
Storms happen
and so do shallow
roots
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Root spread
Issues: construction, covering & stability
certain herbicides problems
yard invasion and suckering
other problems
What does a stem do?
Physically support leaves, buds, flowers & fruits
Transport water, minerals & sugars and other compounds
Provides storage in some plants
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What’s inside the stem?
cortex cells add structural strength to the stem
vascular bundles
corn
Vascular bundle arrangement
herbaceous dicot (sunflower)
Phloem
Xylem
Vascular bundle
Phloem transports photosynthetic products to areas of the plants needing energy
Xylem is like tiny straws and transports water and minerals from the soil to other parts of the plant and out through the leaves
Vascular cambiumcells make more xylem and phloem
Vascular cambium
• Cambium is a meristematic tissue,
meaning it divides to produce new tissues
• Cambium divides to produce
– xylem: to the inside (heartwood, pith)
– phloem: to the outside (part of bark)
• Responsible for “girth growth,” or
increased stem diameter in woody plants
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Stem cross-section
Herbaceous dicot
(clover)Herbaceous monocot
(corn)
xylem
phloem
Notice the relative position of the xylem, phloem, and cambium!
cambium
Herbaceousmonocot (corn)
Stem cross-sections
Woody dicot(maple tree)
Carry H2O & dissolved nutrients
Cells are:
long, open-ended, connected end to end
have thick cell walls
resemble straws
Xylem cells
Xylem cells are really strong. Why?
P. Dahiya: Nature Cell Biology
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Phloem cells
Transport actively photosynthetic products
from leaves to roots, stems, flowers & fruits
Cells are:
long and tube-like
without extra cell wall thickening
vascular cambium
bark
phloem
xylem
What’s this area?
Woody Stem Anatomy
Vascular
Cambium
Sapwood
-
functional
xylem
Inner Bark
(phloem)
Outer Bark
Heartwood -
nonfunctional
xylem
?What is bark?
Answer. Bark is the outer layer of cells on a tree containing
cambium, compressed phloem, and sometimes, cork.
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Stems evolve in response to selection pressure
Thorns for defense (rose) Corky extensions (Euonymus alata)
Photosynthetic stems (Blueberry and Christmas cactus)
Stems selected by humans for storage
Stems evolved for vegetative propagation
External parts of the stem
node = place where leaf is
(or was) attached to
the stem
internode = distance
between nodes
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Lenticel
(breathing pore)
Bud Scale Scar
Leaf Scar
Node
Node
Node
Internode
Terminal Bud
Axillary or
Lateral Bud
Lateral or axillary buds
Located in the angle where the leaf attaches to the stem
Apical dominance
Lateral buds kept dormant due to plant hormone (auxin) cascading from top downwards until auxin source removed
Apical (apex = top) dominance
Auxin= plant growth regulator or “hormone”
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Axillary bud
May produce lateral shoot or branch –less auxin effect further from the apex due to dilution
Auxin and fruit trees
Phototropism –
another auxin effect
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Auxin
Phototropism
Buds and
vegetative
dormancy –
what triggers
the dormancy
process and
what brings
them out of
dormancy?
Winter chilling requirement – hours below 45 degrees
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Leaf Functions
• Use sunlight to make
sugars – photosynthesis
• Use sugars to make
energy and other
compounds – respiration
• Move water from roots
throughout the plant -
transpiration
Major leaf parts
• lamina (leaf blade) -highly variable in size and shape
• petiole - stalk at base of leaf that attaches leaf blade to stem
catching insects
Modified leaves
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floating spinesscales
tendrils Succulence
More modified leaves Leaves modified for storage
leaf blade
petiole
Remember monocots & dicots?
dicots monocot
Monocot or Dicot?
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Leaf arrangement on a stem
opposite
whorled
alternate
These characteristics are important in identifying plants
bedstraw Japanese knotweed
What are the leaf arrangements of these plants?
snowberry
Compound vs. Simple leaves
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Simple leaf
Buds are in the axils between leaf and stem
Compound leaves
pinnately compound palmately compound
leaflet
What’s going on inside the leaf
and plant?
• Photosynthesis
• Respiration
• Transpiration
Balancing act
What is photosynthesis?
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Chloroplasts capture light energy
CO2 + H20 + light energy = sugars + O2
Mid-rib cross-section
central vein
or mid-rib
upper epidermis
lower epidermis
Epidermis
May have special adaptations like hairs or waxy layer that help with drought tolerance
stinging nettle
Other adaptions on the
epidermis?
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Leaf cut-away
mesophyll
Stomata
Stomatal
cycle
Factors that affect
photosynthetic rate
• Carbon dioxide
availability
• Water
• Light (quality, amount,
quantity)
• Temperature
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What is transpiration?
Transpiration is water loss (as vapor) from a plant
Transpiration rate is controlled by opening and closing of the stomates, which is influenced by humidity, temperature, and time of day.
Functions of transpiration
•Cool plant
•Transport
minerals
•Move sugars &
plant chemicals
around
•Maintain turgor
What is turgor?
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Transpiration requires…
• soil moisture
• functional root system
• functional stem & branch
plumbing
• functional leaves
Transpiration Rate
• Transpiration rate is controlled by…
– stomatal aperture
• in response to…
– relative humidity
– temperature
– light
– wind
• under constraint of…
– water availability
– plant nutrition
How does water get from the soil to the top of a tree?
Stomates control evaporation
Root hairs (often with the help of mycorrhizae) absorb water from the soil
Xylem cells transport water via capillary action and cohesive force of water
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Respiration is the opposite of
photosynthesis
In respiration, sugars, water, and oxygen are used to create energy to drive biochemical reactions and carbon dioxide and water are released.
What is respiration? Factors affecting respiration rate
Temperature
Oxygen
Soil condition
Sugars + oxygen = chemical energy + CO2 + H2O
A Comparison
• occurs in sunlight
• uses food
Photosynthesis Respiration
• releases oxygen
• uses carbon dioxide
• uses water
• stores energy
• produces food
• releases energy
• produces water
• releases carbon dioxide
• uses oxygen
• occurs in dark and light
Plant Processes in Balance
• Water Uptake vs Transpiration
• Photosynthesis vs Respiration
• Carbohydrate allocation
• Nutrient allocation
• Growth vs Storage vs Reproduction
vs Defense…
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. How plants reproduce
(or are propagated by clever
gardeners)
Vegetative (asexual)
propagation
Divisions
Cuttings
Layering
Grafting/Budding
Tissue culture
Cuttings
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Responses involving auxin
Formation of
adventitious roots
Layering
Grafting Grafting
Scion
Rootstock
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Tissue cultureCytokinin and auxin & tissue
culture
Flowers and sexual propagation
Flowers facilitate pollination.
If fertilization occurs, seeds are produced and carried in cones (conifers) or fruits (flowering plants)
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Flower Types
• Complete – Has all floral parts present (sepals, petals, stamens, pistils)
• Incomplete -flower lacks 1 or more of the 4 parts
Flower Types, Continued
• Perfect – Has both stamens and pistils (male and female parts)
• Imperfect – Lacks either stamens or pistils
“male” flower
(staminate)
“female” flower
(pistillate)
Complete or Incomplete?Perfect or Imperfect?
Imperfect flowers can be either
monoecious (on the same plant) or
dioecious (on different plants)
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Walnut:
monoecious
Holly:
dioecious
Male and female trees
Pollination
Method: wind, insects, bats, lizards, etc.
Incompatibility: What is it and
why it has evolutionary value?
Hybrids: Mostly man-made but not always
Pollination vs. fertilization
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beetles wind hummingbirds
big leaf maple cape fuchsiawillow
butterflies flies bees
yarrow skunk cabbage cat’s ear
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Dranuculus
vulgaris
Carrion beetles
? Can you think of any modified
flowers?
Hint: think veggies!
pollen grains
ovary
pollen tube
ovule
Fertilization
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Seed dispersal
• Wind
• Water
• Animals
• Insects
• Others
Fruit: Facilitates seed dispersal
185
Seeds release hormones that cause cells to divide
and expand. When seeds are only on one side
lopsided fruit results.
Very incomplete pollination = fruit drop
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Ethylene
Fruit ripening
Five plant growth regulators
Auxins
Gibberellins
Abscisic acid
Cytokinins
Ethylene
Auxin
Apical dominance
Phototropism
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Gibberellic acid
Stimulate cell division and elongation
Speeds seed germination
Breaks seed dormancy
Abscisic acid
Induce and maintain dormancy
Control stomatal closure
Leaf abscision
Cytokinins
Stimulate cell division
Delay senescence
Ethylene
Stress response: epinasty and leaf drop
Fruit ripening
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