Origin of the Land Plants. Alternation of Generations.

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)