Green algae

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Green algae Land Plants
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Algae

• Named for their green chloroplasts
• Single celled (Chlamydomonas)
• Single celled colonial (Volvox)
• multicellular thallose mats (Ulva)

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Multicellularity

• Model begins with colonial algae, like Volvox
• Formation of colonies
• Specialization of cells
• Interdependence of cells

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Algae life cycle

• Alternate generations
• Multicellular diploid haploid forms
• Gametes of similar size
• n and 2n stages are independent
• n stage gametophyte
• 2n stage sporophyte
• Morphological differences between n and 2n stages
  are slight to non-existent

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Algae life cycle
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Plants evolved from green algae

• Evidence
• Green chloroplasts
• Similar cell wall construction machinery
• Similar mechanism for forming cell plate during
  division
• Similar enzymes in peroxisomes
• Flagellated sperm
• Genetic similarity

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Synapomorphies of Green Plants

• Apical meristems
• Alteration of haploid and diploid generations
• Walled spores in sporangia
• Male female gametangia
• Multicellular, dependent embryos

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Synapomorphies reflect Adaptation for life on land

• Absorbing transporting resources
• Air and water provide different resources
• Transport nutrients H2O (xylem, phloem) from
  one part of plant to another
• Support body against gravity (lignin)
• Preventing dessiccation
• Maintain moisture while exchanging gases
  (cuticle stomata)
• Spread gametes in dry, high-gravity environment
• Shield offspring from harsh environment

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Adaptations for terrestrial life
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Plant phylogeny

• Nonvascular Plants (Bryophytes)
• Liverworts, hornworts, mosses
• Vascular plants
• Seedless
• Pterophytes (ferns)
• Lycophytes (club mosses)
• Seed plants
• Gymnosperms (conifers)
• Angiosperms (Flowering plants)

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Bryophytes

• 475 Mya
• Apical meristems
• Embryos contained in parent plant - gametophyte
  (n) is dominant

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Seedless Vascular Plants

• 420 Mya
• Lignin-hardened vascular tissues
• Roots, stems, fronds
• Sporophyte (2n) is dominant life stage

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Seed Plants

• 360 Mya
• Seeds! protective covering food supply
  (endosperm)
• Prevent dessication, microbial attack
• Pollen dispersed
• Eliminates reliance on water allows wide
  dispersal

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Angiosperms

• 140 Mya
• Flowers reproductive structures modified to
  attract pollinators
• Modified seed coats Fruits Enhance dispersal
• Stick to animal fur, use digestive tracts,
  stimulated by fire

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Seeds Fruits

• Ovule develops into seed
• Ovule develops into fruit