origin of the land plants. alternation of generations

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  • Origin of the Land Plants

  • Alternation of Generations

  • Charophycean AlgaeDont display alternation of generationsMost closely related to land plants by homologyOrganisms are haploidExamples: Chara and ColeochaeteSingle-celled zygote produces haploid spores by meiosisGametes are bi-flagellate

  • Homologies Between Charophyceans and Land PlantsChloroplasts have chlorophyll a & b, carotenoids and other accessory pigmentsCell walls with cellulose (20-26%)Peroxisomes with anti-photorespiration enzymesPhragmoplasts for cell plate formationRosette cellulose-synthesizing complexes Molecular systematics: DNA, rRNA, chloroplast DNA

  • Chara Pond Algae

  • Challenges of Moving to LandLack of moistureUltraviolet lightSeparation of water, minerals, and carbon source (CO2)Lack of support for the plant bodyRapidly changing environmental conditions

  • BryophytesNonvascular plantsDominant form is the haploid gametophyteSwimming gametes require waterDiploid dependent sporophyte produces haploid spores by meiosis.Spores grow into gametophyte plants that produce haploid gametes by mitosis.Mosses, liverworts, hornworts

  • LiverwortGemmae cups of Marchantia

  • Marchantia

  • MossSporophyte and capsuleGametophyte plant (n)

  • Polytrichum - Moss

  • Peat Bogs Store Carbon

  • Spagnum Moss


  • Pteridophytes (Seedless Vascular Plants)Branched, independent sporophytesSporophytes are the dominant plantAsexual reproduction: SporesSexual reproduction: GametesSwimming gametes require waterPossess Xylem and PhloemTrue roots, stems and leaves in some groups

  • Lycophyta: Club MossesPterophyta: Whisk FernsSphenophyta: HorsetailsPterophyta: Ferns

  • LycophytaWoody trees dominating Carboniferous period (300 mya)Epiphytes Air PlantsClub-shaped spore-bearing cones called strobiliSpores very flammable

  • SphenophytaWoody trees during Carboniferous periodHollow ribbed stems jointed at nodesSilica (silicon dioxide) granulesEquisetum hyemale or Scouring rush

  • Polypodium fern

  • Fern Life Cycle

  • Sori on lower side of frond

  • Sorus and mature sporangium

  • Fern Prothalus(Gametophyte Plant)


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