Exercise 4 - Bryophytes: The First Land Plants

• Charophyceae from which they had inherited membrane-bound organelles, cellulosic cell walls, chlorophyll a and b, and development of
• Structural modifications that permit high survival of plants on land

  • Protective jacket of cells surrounding egg- and sperm-producing structures (the archegonia and antheridia, respectively)
  • Protective layer of cells covering the spore-producing structures (sporangia)
  • Protective embryo
  • Waxy coating called cuticle on the aerial parts
  • Specialized cells for water and food conduction
• These structures also support the diplohaplontic life cycle of plants
• The first groups of plants are the bryophytes or the nonvascular plants which are thought to be among the first plants to dominate the ancient terrestrial environment approximately 400 MYA.
• There are about 24,000 species of bryophytes that are unevenly divided into the three groups – the

  Liverworts (Division Marchantiophyta)

  Hornworts (Division Anthocerophyta)

  Mosses (Division Bryophyta)
• Two important characteristics distinguish bryophytes from vascular plants:

  1. the absence of specialized vascular tissue: xylem and phloem, and
  2. the sporophyte is nutritionally dependent upon the gametophyte.
• Liverworts - Division Marchantiophyta (also known as Hepatophyta) are composed mainly of liverworts. The term “liverwort” was coined from the words, “wort” (means small plant) and “liver” due to its lobe-like thallus (a flattish green sheet structure or body of its gametophyte) which resembles a liver.
• Types of Liverworts

  1. Thallose Liverworts - liverworts with lobe-like, flattened, branching thallus

  * Complex Thallose Liverworts - have thallus that is many cells thick and the cells in different layers within the thallus have different function.

  * Simple Thallose Liverworts - thallose liverworts in which there is no such differentiation of cell function within the thallus.

  
  

  2. Leafy Liverworts - liverworts which produce flattened “stem” with overlapping scales or "leaves" in three ranks
• Morphology of Liverworts

  Thallose Liverwort (Pellia epiphylla)

  Leaf and amphigastria arrangement varies per species

  • Lophocolea sp. (succubous arrangement)
  • Bazzani sp. (incubous arrangement)
• Hornworts - Division Anthocerotophyta are characterized by a thallose gametophyte usually having a thin rosette or ribbon-like thallus, howerver, its sporophyte are generally erect, photosynthetic and needle-like.
• Hornworts possess pyrenoids (protein body which store starch and are commonly found in green algae), have one chloroplast per cell and lack oil bodies.
• Many hornworts also develop internal mucilage-filled cavities that are occupied by cyanobacteria like Nostoc. These cyanobacteria colonies give the hornwort a distinctive blue-green color.
• Mosses - Division Bryophyta typically grows from 1 to 10 cm tall and are ubiquitous in nature. These thrive in diverse habitats all around the world but commonly grow closely in clumps under shady or moist places.
• Mosses are also classified into ectohydric, endohydric and myxohydric based on their water-conducting pathways.

  • Ectohydric mosses relies on ecternal source of water and assimilate water through capillarity.
  • Endohydric mosses consist primitive vascular structure which functionally resembles the xylem and phloem. These are the leptome which conducts the photoassimilates and the hydromel that conducts water.
  • Myxohydric mosses are capable to utilize both pathways.
• Life Cycle of Non-vascular Plants

  The basic bryophyte life cycle begins with a haploid spore that germinates on moist soils and grows into a filamentous protonema which later develops into a thallose or leafy gametophyte.
• Mature gametophytes produce antheridia or archegonia, depending on the sex. When their habitat is flooded with rainwater, the sperms emerge from antheridia and swim to the archegonium, where one sperm fertilizes one egg to form a diploid zygote.
• A diploid sporophyte develops within the archegonium and as it matures it produces a sporangium. Meiosis occurs within the sporangium resulting in the production of haploid spores.