evolution of land plants Flashcards
red algae
evolved into seaweeds and protists
glaucophytes
- rare, 13-15 species
- evolutionary dead end, did not evolve into other lineages
Class charophycaea
- evolved from green algae (chlorophytes)
- embryophyta clade (terrestrial plants) evolved from this class
- share common characteristics with land plants
characteristics land plants and charophycaea share
- cellulose cell walls
- starch synthesis and storage in stroma of chloroplast
- chlorophyll b, lutein and beta carotene accessory pigments
- granal stacks
- 2 membranes around chloroplasts
- many not found in algae
land colonisation by plants
by mid-Ordovician ~470mya
environmental changes that allowed plants to colonise land
- in Cambrian and Ordovician
- tectonic and glaciation events meant atmospheric CO2 increased and temperature decreased
- glaciation led to low sea level (shallow semi-aquatic areas and increased terrestrial habitat area)
- formation of rudimentary soil from chemical weathering and lichen
physiological/morphological changes that allowed plants to colonise land
- diplobiontic life cycle meant thousands of spores produced, can cover large area to find advantageous conditions and then evolve to fit that niche
- elaboration of sporophyte stage and reduction of complexity of gametophyte, as it is water dependent
- evolution of characteristics to aid water retention
evolution of characteristics to aid water retention
- vascular elements 475mya, basic strong hollow cells
- evolution of thin cuticle 450mya
- evolution of spores resistant to desiccation 420mya
- evolution of stomata 420mya (cuticle can then thicken)
- evolution of lignin 415mya
- evolution of early roots as sediment increases
impact of plant colonisation on terrestrial ecosystems
- stabilisation of river banks
- channeling of rivers
- muddy flood plains (sediment deposits from biological weathering)
- soil formation
- peat deposits
- significant chemical weathering (acid from roots)
some species of chlorophytes are diplobiontic
- alternation of generations, diploid and haploid stage of life cycle
- both stages undifferentiable from each other
- haploid gametophyte produces haploid male and female gametes that fertilised and grow into sporophyte
- diploid sporophyte produces undifferentiated haploid spores which grow into the gametophyte
evolution of trees
~300mya
evolution of supporting elements
- the stele (centralisation of vascular elements)
- extensive underground roots
- trunk with bark
- root mantles
small leaves
- compartmentalisation of photosynthetic apparatus meant they were not interfering with strengthening elements (bark)
Gilboa tree
- first tree, 385mya mid Devonian
- leafless photosynthetic branches
- height mainly to aid seed dispersal
- found in waterlogged low oxygen soils
- went extinct in late devonian
evolution of life cycle, transition to heterospory
- gametophyte reduced down to ovule and pollen (undifferentiated spores from sporophyte differentiate)
- development of one functional megasporangium (ovule) that is retained
- evolution of true pollen, spore is release and floats around until it meets female part, travels down tube to ovule and then releases sperm
mid devonian and early carboniferous
- evolution of small vascualr plants to trees
- forests cover a large percentage of land
- shift in climate from hot and humid to cold and arid (drop in CO2 levels from carbon deposits, increase in O2)
- evolution of spore and seed producing lineages
- evolution of gymnosperms
evolution of angiosperms, flowering plants
- 138mya, lower cretaceous
- early angiosperms had small inconspicuous flowers that often lacked petals, as did not evolve alongside insects
- had male and female flowers
- probably herbaceous but possibly aquatic
- evolution of sticky pollen, utilising insects for pollen dispersal meaning greater dispersal distances
