Evolution of Plants

Plant Evolution

All Plants have Alternation of Generations  gametophyte….  plant body that produces gametes  Sporophyte –plant body makes spores  Spore =  reproductive structure protected by hard wall. Used for dispersal. germinates by breaking out of wall.

 Spores (1n) germinate and grow into gametophytes (1n)  Gametes fuse and grow into sporophytes(2n)  Sporophytes 2n….make spores (1n) by  meiosis  Gametophytes 1n …make gametes by  mitosis

Charophytes: Link btwn plants & algae  Charophytes no alternation of generation  so not plant  Produce cellulose cells walls in same unique fashion, Chloroplast DNA similar  Only non-plant with anti-photorespiration enzymes

True plants with alternation of generations (evolved 50 mya)  Primitive plants have:  a) swimming sperm  b) gametophyte dominant  c) sporophyte supported by gametophyte  d) no veins  e) no seeds

Ordovician : Ozone allows first land plants shared derived trait: waxy cuticle

Advantages to life on land  More direct sunlight  Higher CO 2 concentration  Soil nutrients  No herbivores

Challenges to Life on Land  Desiccation  Lack of support vs gravity

Silurian : 1 st vascular plants = have veins to transport H 2 O & sugars  Rhyniophytes  Seedless, only stems but no roots or leaves

Devoinan: Seedless vascular plants : Lycophytes, horsetails & ferns  New trait: upright growth due to lignin in cell walls  First dominant sporophyte  But still primitive with swimming sperm & no seeds  Underwent adaptive radiation took over Devonian swamps

Lycophytes :club moss or ground pines

Horse tails: scouring rushes

Ferns  These are sporophytes  sori full of spores  Gametophytes microscopic

Carboniferous Period: coal deposits form  Seedless vascular plants as tall as trees  Δ sea level dry out and flood swamps  Layers of dead plants build up faster than they  decompose

Carboniferous = first conifers  Conifers = seed plants with cones  Gymnosperms = ‘naked’ seeds  Ovules fertilized by sperm nuclei carried in pollen  Pollen = freedom from water, it is carried by wind so can disperse on land

Advantage of Seeds  Multicellular vs spores unicellular  Have stored energy  (starch/oil)  1) allows delayed germination  2)enhanced early growth  Protective coating over embryo  May have Fruit or dispersal aids

Angiosperms = flowering plants  Seed plants with flowers  Seeds form in Ovary of flower  Ovary may form fruit  Most modern group now 90% of all plant species  Reproductive adaptation to pollinators

All but bryophytes…  Dominant sporophyte (2n) grows from embryo  Small gametophyte (1n)