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Kingdom Plantae
Plant Diversity II
Professor Andrea Garrison
Biology 3A
Illustrations ©2014 Cengage Learning unless otherwise
noted
Text ©2014 Andrea Garrison
Plant Diversity II
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Plant Classification
• Bryophytes – nonvascular plants
– Phylum Hepatophyta – liverworts
– Phylum Anthocerophyta – hornworts
– Phylum Bryophyta – mosses
• Seedless vascular plants
– Phylum Lycophyta – club mosses
– Phylum Pterophyta – ferns
– Phylum Psilotophyta – whisk ferns (text incl in Pterophyta)
– Phylum Sphenophyta – horsetails (text incl in Pterophyta)
• Now we move into seed plants 
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Gymnosperms
• Seed not enclosed
inside fruit
(gymn=naked;
sperm=seed)
• Seeds inside cone or
similar structure
• Conifers, Ginkgos,
Cycads (sego palms)
• Sizeable trees, shrubs
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Gymnosperm Trends in Plant Evolution
• New adaptations allowed gymnosperms to be
successful in a variety of new environments
– Increased size
– Major changes in methods of reproduction
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Further Trends in Plant Evolution
• Increased size
– Apical meristem allowed increase in height
– Evolution of lateral meristem allowed secondary
growth
• Increase in diameter as plant ages
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Further Trends in Plant Evolution
• Reproductive adaptations
– Heterospory
– Sporophyte produces:
• Microspores  male gametophyte
• Megaspores  female gametophyte
– Retained inside sporangium and covered with integument
• Over time
– Microspores  male gametophyte  pollen
» Many fossilized pollen grains from this period (Devonian)
– Megaspores developed integument
» Retained inside reproductive structure
» Similar to modern ovule which develops into seed
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Modern Gymnosperms
• Spores sheltered inside parent plants
– Different than seedless plants which disperse spores
– Sporophyte produce haploid spores
• Retained inside reproductive structures
• Grow into multicellular gametophytes
– Male gametophyte = pollen grain
» 2 non-motile sperm develop inside each pollen grain
– Female gametophyte with egg develops inside ovule
• Protected gametophytes more likely to survive
– Hidden inside parent sporophyte
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Modern Gymnosperms
• Pollination = transfer of pollen to female
reproductive parts of plant
– Accomplished by air, insects, birds
• Pollen grain grows into ovule and releases sperm
• Reproduction no longer requires water
– A few gymnosperms still have motile sperm that swim
to egg
• Cycads & Ginkgoes
• Not very successful (few species)
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Modern Gymnosperms
• Pollination leads to fertilization
• Fertilization produces sporophyte embryo
• Seed = embryo + food reserves for embryo
+ tough outer coat
– Much tougher than spores and small
gametophytes, so seed species very successful
– Gymnosperm seed food reserves come from
tissues of female gametophyte
• Embryo (in seed) grows in reproductive
structure
– Same place where female gametophyte
produced the egg
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Phylum Coniferophyta
• Most common gymnosperms
–
–
–
–
Pines trees
Sequoias > 80 m tall
Redwoods >112m tall
Bristlecone pine
• One specimen >5000 yrs
• Most evergreens
– Shed some old leaves, but
keep most of them
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Phylum Coniferophyta
• Needle-like or scale-like
leaves
–
–
–
–
Adapted to dry habitats
Thick cuticle
Sunken stomata
Fibrous epidermis
Plant Diversity II; photos: top & bottom left by A. Garrison; bottom right by Walter Sigmund,
http://creativecommons.org/licenses/by-sa/3.0/legalcode
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Phylum Coniferophyta
• Seeds inside cones (strobili)
Plant Diversity II; photos by Didier Descouens, http://creativecommons.org/licenses/bysa/3.0/deed.en
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Phylum Coniferophyta
• Seeds inside cones (strobili)
Plant Diversity II; photo by A. Garrison
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Phylum Coniferophyta
• Male and female cones
dimorphic
• Male cones smaller, fragile
– Scales = sporophylls
– 2 microsporangia develop on
underside of each scale
• Produce microspores
– Develop into pollen
Plant Diversity II; photo by Menchi,
http://commons.wikimedia.org/wiki/Commons:GNU_Free_Documentation_License
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Phylum Coniferophyta
• Male and female cones
dimorphic
• Females larger, longer lived
– Develop higher in tree
– Scales = sporophylls
– 2 ovules develop on each scale
• Megasporocyte in each ovule
– Meiosis  4 megaspores
– Only 1 megaspore survives
– Matures into female gametophyte
slowly ( 1 yr in pine trees)
» Completed during pollination
» Several archegonia w/1 egg
each
Plant Diversity II; photo by A. Garrison
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Phylum Coniferophyta
• Single tree may produce billions of
pollen grains
• Female cone structure channels air
currents to deposit pollen grains
• Once pollinated, scales close up
– Seed development can take up to 2 yrs
• Pollen grain grows tube into ovule
• Sperm released and fertilize egg
• Seed forms
– Scales open up and seeds released
– Some cones require fire for scales to
open
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Phylum Coniferophyta
• Seeds have wings that
catch wind and help with
dispersal of species
Plant Diversity II; phots by Didier Descouens, http://creativecommons.org/licenses/bysa/3.0/deed.en
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Coniferophyta
Life Cycle
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Phylum Cycadophyta
• Sego palms
• Strobilus in center
– Clusters of sporophylls
• Bear pollen or ovules
• Pollinated by air or
beetles
– Some tissues toxic
• Seeds and flour edible if
toxins rinsed away
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Phylum Ginkgophyta
• Fan-shaped leaves
– Only found in wild in
China
– Grown in nurseries
– Male is popular for
landscaping
– Female has fleshy seeds
with foul odor
Plant Diversity II; photo by A. Garrison
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Angiosperms
• Flowering plants
• Seeds enclosed in carpel
(angi = enclosed; sperm =
seed)
– Carpel later produces fruit
• Most diverse plants on
earth
– Duckweed (1mm);
Eucalyptus (100m)
• All angiospserms assigned
to phylum Anthophyta
(antho = flower; phyt =
plant)
Plant Diversity II; photo by A. Garrison
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Phylum Anthophyta
• Very abrupt appearance
in fossil record
– Evolutionary history not
well understood
• Several clades
– Basal angiosperms
• Not monophyletic
• Magnolias, avocados
– Most monocots or
eudicots
• Based on plant structure
Plant Diversity II; photo by A. Garrison
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Further Evolutionary Trends
• Modification of vascular tissue
– Allow more rapid transport of water up from roots and P/S
products down from leaves
• Flower = reproductive structure
– Contribute to reproductive success of plants that bear
them
• Enhanced nutrition and protection for embryos
– Double fertilization forms diploid zygote and nutritive
tissue (endosperm)
– Ovule enclosed in ovary
• Protects against desiccation and predation
• Develops into fruit
– Protects and disperses seeds
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Further Evolutionary Trends
• Most angiosperms require pollinators
– Internal flower structure complex
– Plants coevolved with specific types of pollinators
• Hereditary change in one species puts selective
pressure on species that use it as a resource
– Nectar food source for many animal species
• As flowers changed, animal species changed with it
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Further Evolutionary Trends
• Most angiosperms require pollinators
– Most flowers structured so pollen rubs off onto
animals that feed from it
• Birds, bats, insects, rodents, etc.
• Flowers with deep calyx pollinated by hummingbirds or
moths with long mouthparts
• Sweet scent attracts ants, bees
• Foul scent attracts flies, beetles
• Some flowers have target in center of plant only seen in
UV light
– Bees see with UV light
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Anthophyte
Life Cycle
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THE END
Modern Gymnosperms
• Coniferophyta
– Needle-like or scale-like
leaves
•
•
•
•
Adapted to dry habitats
Thick cuticle
Sunken stomata
Fibrous epidermis
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