Plants (Kingdom Plantae)
• Multicellular eukaryotes
• Photoautotrophs
• Terrestrial?
– Not all plants are terrestrial
• Return to water from land
• Move to land was a major step
Move to Land Required Significant
Adaptations
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Water uptake and loss
Gas exchange
Reproduction
Support
Move to Land
• Plants probably
evolved from a group
of green algae called
the charophytes
• Are a fringe species
exhibiting
multicellular traits
• Why a fringe
species?
Features Common to Green Algae and
Plants
• Chlorophyll a and other accessory
pigments (Chl b, b-carotene)
• thylakoid membranes stacked into grana
Features Common to Green Algae and
Plants
• Chlorophyll a and other accessory
pigments (Chl b, b-carotene)
• similar photosynthesizing organelles
• cell walls of cellulose
• store carbohydrates as starch
• alternation of generation
Highlights of Plant Evolution
• Four major periods
• Move onto land (~425 - 475 mya)
– prevent desiccation of whole plant
– protect reproductive structures
– Features seen in mosses (bryophytes)
Highlights of Plant Evolution
• Evolution of vascular tissue and
diversification (~400 mya)
– simple diffusion not an option
– Mosses - water-conducting tubes
– transport and support
– larger body size
These are features first seen in ferns, horsetail,
whisk ferns
****Similar protection of gametes
Whisk Fern
Horsetail
Highlights of Plant Evolution
• Evolution of seed (~360 mya)
– additional protection from desiccation
and predation
– dispersal
Highlights of Plant Evolution
• Emergence of flowering plants (~130 mya)
– Seeds in protective ovary
– Expanded potential for diversity
– Complex structure with great potential
for adaptation
– Greater sexual reproductive success
– Coevolution between insects and
angiosperms
Nontracheophytes
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Mosses, liverworts and hornworts
Probably closest to ancestral form
protected gametangia
lack vascular tissue
Encrusting
Water needed for fertilization
Gametophyte
Sporophyte
Sporophyte relies on gametophyte for nutrients
Nonseed Tracheophytes Plants
• Ferns, horsetail, club mosses
• Retain some traits of mosses
• Evolved some traits also seen in seedproducing vascular plants
Traits Shared with Nontracheophytes
• Antheridia and archegonia retain similar
structure
• Require water/moisture for sexual
reproduction
• Production of spores
Traits Shared with Seed-Producing Plants
• Vascular tissue - greater body size
• Sporophyte is dominant stage of life cycle
Sporophyte
Gametophyte
Seedless tracheophytes were the dominant
vascular plants for ~ 50 million years
• Continents in tropical/subtropical zone
• As continents drifted away from equator,
conditions changed
• Seed-producing plants were present
during height of seedless vascular plant
success
Rise of Seed-Producing Tracheophytes
• Well suited for environmental changes
• Gametophyte smaller and retained in
moist tissues of sporophyte
• Pollination rather than swimming sperm
• Evolution of seed
• gymnosperms and angiosperms
Gymnosperm
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“naked seed”
still have a seed coat
four divisions
Coniferophyta best known
evergreens
needle-shaped leaves, thick cuticle
Sporophyte
Gametophyte
Gametophyte passes within sporophyte
Angiosperms
• “protected seed”
• most diverse group
– 235,000 known species vs. 721 species of
gymnosperms
• One division - Anthophyta
• Two classes
– Monocotyledones
– Dicotyledones
Angiosperms
• successful and effective design
• different themes of the same design
Sporophyte
Gametophyte
Gametophyte passes within sporophyte
Develops
into fruit
Develop into
seeds