Bryophytes

• non-vascular • Include Marchantiophyta (liverworts), Bryophyta (mosses) and Anthocerophyta (hornworts) - a basal grade, not a clade

• More carbon dioxide in the atmosphere - diffuses 1000x faster through air than in water • Aquatic algae can be starved of carbon dioxide when it photosynthesises fast - limits photosynthesis • Carbon dioxide is not a limiting factor on the land

• Cuticle: waxy, waterproof polymer coating cells which protects against desiccation Provides a problem: access to carbon dioxide becomes harder requiring pores • Pores for gas exchange: multi cell structure that allows carbon dioxide in • Gametangia (antheridia - sperm sac and archegonium - egg sacs) with multicellular jacket: sterile jacket protects against desiccation • Spores with sporopollenin: useful for dispersal through the dry atmosphere as the coating protects from desiccation

• thallus structure with dichotomous branching • cells that store water • rhizoid • small • similar to earliest terrestrial plants • simple pores that are always open

• Haploid thallus • Develops gametangia on the surface of the thallus (produced by mitosis) • Rain allows sperm to swim to the egg sacs (form a diploid zygote) • Zygote undergoes cell divisions in the egg sac, forming an embryo • Eventually embryo grows diploid plant on the haploid thallus • Diploid plant has a sporangium (like a capsule) which produces spores by meiosis • Spores are released and dispersed through the air to grow into haploid thallus

• moss • Gametophyte: long and green vertical axis with branching leaves (some can be relatively complex) • Usually small but can be half a metre tall (raises the photosynthetic leaves closer to the sun) • Vertical axis is favoured by evolution to overcome competition for sunlight • In the centre of the axis is a conducting strand (made of two cells: hydroids for water and leptoids for dissolved sugar). Why are they not vascular? In vascular plants the vascular system acts as a skeletal system which does not happen in moss

• Haploid gametophytes are either male or female • Antheridia clustered in splash cups at the tip of leaf axis • Archegonia is clustered at the tip of the leafy axis Rain splashes sperm to female egg sac to form diploid zygote • Sporophyte: polytrichum emerges from leafy gametophyte where spores can be dispersed

• 100 species • Closest related group to vascular plants • Have leafy thalloid gametophytes and erect sporophytes grow out of the thallus • Sporophytes have pores with guard cells allowing them more control over gas exchange. They are also long-lived and capable of photosynthesis • Intercalary growth: sporophytes grow from the base and the tip with the spores is the oldest

haploid plant that produces haploid gametes by mitosis.

diploid plant that produces haploid spores by meiosis.

• Rapid radiation of bryophytes caused atmospheric carbon dioxide levels to plummet • Atmospheric carbon dioxide was stored in soil and plants • Creation of soil increased speed of geochemical cycles (allowed for breakdown of parent material)

• all have a single axis, no branching and one terminal sporangium • lateral spore sacs allow for more spores to be produced

• Wetland ecosystems where accumulation of peat which forms faster than it decomposes due to acidity and lack of oxygen • Peat can accumulate in 10-20m depths (50m in Siberian peat soils) • Peat soils contain 20-30% of world’s soil organic carbon • As climate warms, the peat soil is being decomposed, returning carbon dioxide to the atmosphere