Origin of the Land Plants
Alternation of Generations
Charophycean Algae
• Don’t display alternation of generations
• Most closely related to land plants by homology
• Organisms are haploid
• Examples: Chara and Coleochaete
• Single-celled zygote produces haploid spores by meiosis
• Gametes are bi-flagellate
Homologies Between Charophyceans and Land Plants• Chloroplasts have chlorophyll a & b,
carotenoids and other accessory pigments
• Cell walls with cellulose (20-26%)
• Peroxisomes with anti-photorespiration enzymes
• Phragmoplasts for cell plate formation
• Rosette cellulose-synthesizing complexes
• Molecular systematics: DNA, rRNA, chloroplast DNA
Chara –Pond Algae
Challenges of Moving to Land
• Lack of moisture
• Ultraviolet light
• Separation of water, minerals, and carbon source (CO2)
• Lack of support for the plant body
• Rapidly changing environmental conditions
Bryophytes
• Nonvascular plants
• Dominant form is the haploid gametophyte
• Swimming gametes require water
• Diploid dependent sporophyte produces haploid spores by meiosis.
• Spores grow into gametophyte plants that produce haploid gametes by mitosis.
• Mosses, liverworts, hornworts
Liverwort
Gemmae cups of Marchantia
Marchantia
Moss
Sporophyte and capsule
Gametophyte plant (n)
Polytrichum - Moss
Peat Bogs Store Carbon
Spagnum Moss
VASCULAR PLANTS(TRACHEOPHYTES)
•Branched, independent sporophytes
•Sporophytes are the dominant plant
•Asexual reproduction: Spores
•Sexual reproduction: Gametes
•Swimming gametes require water
•Possess Xylem and Phloem
•True roots, stems and leaves in some groups
Pteridophytes (Seedless Vascular Plants)
Lycophyta: Club Mosses Pterophyta: Whisk Ferns
Sphenophyta: Horsetails Pterophyta: Ferns
Lycophyta
• Woody trees dominating Carboniferous period (300 mya)
• Epiphytes – “Air Plants”
• Club-shaped spore-bearing cones called strobili
• Spores very flammable
Sphenophyta
• Woody trees during Carboniferous period
• Hollow ribbed stems jointed at nodes
• Silica (silicon dioxide) granules
• Equisetum hyemale or Scouring rush
Polypodium fern
Fern Life Cycle
Sori on lower side of frond
Sorus and mature sporangium
Fern Prothalus(Gametophyte Plant)