Exercise 4: Bryophytes: The First Land Plants

• Structures supporting the diplohaplontic life cycle of plants: 1) archegonia, and antheridia ; 2)sporangia ; 3) protective embryo ; 4) cuticle ; 5) specialized cells for food and water conduction
• Kingdom Plantae represents a very large group of mostly terrestrial organisms composed of over 250,000 species of plants
• Plants have ancestral ties with green algae (Charophyceae) and have inherited membrane-bound organelles, cellulosic cell walls, chlorophyll a and b, and development of phragmoplast
• Most bryophytes are small, usually less than 20 mm in height
• Two important characteristics distinguishing bryophytes from vascular plants are the absence of specialized vascular tissue (xylem and phloem) and the sporophyte being nutritionally dependent upon the gametophyte
• Groups of bryophytes

  • Liverworts (Division Marchantiophyta)
  • Hornworts (Division Anthocerophyta)
  • Mosses (Division Bryophyta)
• Bryophytes are found in almost all terrestrial habitats, showing the greatest diversity in moist habitats
• Structural modifications for survival on land

  • Protective jacket of cells surrounding egg- and sperm-producing structures (archegonia and antheridia)
  • Protective layer of cells covering spore-producing structures (sporangia)
  • Protective embryo
  • Waxy coating called cuticle on aerial parts
  • Specialized cells for water and food conduction
• Bryophytes are the first plants to dominate the ancient terrestrial environment approximately 400 MYA
• Types of Liverworts

  • Thallose Liverworts: Complex Thallose Liverworts, Simple Thallose Liverworts
  • Leafy Liverworts: liverworts with lobe-like, flattened, branching thallus, liverworts which produce flattened "stem" with overlapping scales or "leaves" in three ranks
• Transition of most plants from an aquatic to a terrestrial lifestyle induced structural modifications for high survival on land
• Molecular systematists have found similarities in some nuclear genes and ribosomal RNA in both charophytes and plants supporting their ancestral ties
• Division Marchantiophyta (Liverworts) are composed mainly of liverworts, small non-flowering, spore-producing plants
• Thallose liverwort


  • Pellia epiphylla
• Mosses thrive in diverse habitats all around the world but commonly grow closely in clumps under shady or moist places
• Hornworts are characterized by a thallose gametophyte usually having a thin rosette or ribbon-like thallus, however, its sporophyte are generally erect, photosynthetic and needle-like
• Liverworts produce flattened “stem” with overlapping scales or “leaves” in three ranks
• Mosses are small, leafy, dioecious bryophytes that typically grow from 1 to 10 cm tall and are ubiquitous in nature
• Gametophytes of moss externally resemble that of the flowering plants, in terms of having stems, leaves, nodes, internodes, and buds
• Hornworts uniquely possess pyrenoids, have one chloroplast per cell, and lack oil bodies (Glime, 2017)
• Many hornworts develop internal mucilage-filled cavities that are occupied by cyanobacteria like Nostoc, giving them a distinctive blue-green color
• 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, the dominant phase in its life cycle
• Mosses are classified into ectohydric, endohydric, and myxohydric based on their water-conducting pathways
• Distinguish between gametophyte and sporophyte generations in each of the above divisions
• By the end of this exercise, students should be able to identify and characterize members of the divisions Marchantiophyta, Anthocerophyta, and Bryophyta
• Differentiate a leafy liverwort from a moss
• Major Clades of the Bryophyta include Basal Moss, Longitudinal dehiscence of Capsule, Peristomal Mosses, and Complex Peristome
• Rain stimulates the antheridia to release sperm that fertilize the egg contained within the archegonium. Fertilization leads to the formation of a zygote, which later develops into an embryo. Diploid sporophytes develop within swollen archegonia
• Representative species

  • Sphagnum sp.
  • Mnium sp.
  • Fissidens sp.
• Life cycle of a bryophyte

  It starts with a haploid spore that germinates on moist soils and grows into a filamentous protonema which later develops into a thallose or leafy gametophyte, the dominant phase in its life cycle. Gametophytes are dioecious, producing antheridia or archegonia. When flooded with rainwater, sperms emerge from antheridia and swim to the archegonium for fertilization, forming a diploid zygote. A diploid sporophyte develops within the archegonium, producing a sporangium where meiosis occurs, resulting in the production of haploid spores
• Parts of a liverwort sporophyte

  • Foot
  • Capsule
  • Seta
  • Elaters
  • Spores
  • Protonema
• Parts of a Leafy Liverwort Gametophyte

  • Thallus - dorsoventrally flattened and resembles minute mosses
  • Stem - cylindrical and give rise to rhizoids and three ranks of leaves
  • Lateral appendages - leaves found on the dorsal side
  • Amphigastria - median appendages (smaller leaves) found on the ventral side. The “leaves” have serrated margins and do not have any thickening (midrib or costa)
  • Rhizoids - hair-like projections at the ventral surface of thallus
• The non-photosynthetic sporophyte of Marchantia sp. is ventrally located under the disk of the archegoniophore. Both the gametangia and sporangia of Riccia are sunken in its thallus. It produces a simple sporophyte within the archegonia and the spores are only released when its thallus age and die (Mauseth, 2008)
• Water flows through these tissues by simple diffusion. In the family Polytrichaceae
• Parts of a Hornwort Gametophyte

  • Thallus - orbicular thallose gametophyte lying on the surface of the ground
  • Sporophyte - erect, horn-like structure arising from the thallus
  • Rhizoids - ventral hair-like projections
• Parts of a Moss

  • Stem - erect, anchored to a substrate through rhizoids
  • Rhizoids - brown thread-like structures which attached plant to substrate
  • Leaves - consist smooth margin and a thickened axis called costa that arise from the “stem” in two ranks. These are also composed of one layer of parenchymatous cells. Notice its arrangement on the stem
  • Sporophyte - erect, arises at the terminal end of the stem, exhibiting a long seta (stalk) and a short cylindrical capsule. The foot is embedded in the gametophyte
• Parts of a Hepatophyta (Liverwort)

  • Capsule - spherical and ellipsoidal, site of spore production
  • Seta - connects the foot and the capsule
  • Elaters - spring-like outer-cover covering that will push open the wall of the capsule to scatter the spores when the capsule bursts
  • Spores - found inside the capsule
  • Protonema - filaments which will grow and form mature gametophyte
• Parts of a Hornwort Sporophyte

  • Foot - found at the bottom of sporophyte; globular group of cells that receive nutrients from parent gametophyte and anchors the sporophyte in place
  • Intercalary system - found in the middle of the sporophyte just above the foot; produce new cells that will form into capsule
  • Capsule - elongated structure connected to the intercalary meristem
  • Capsule wall - surface cells of the capsule which are sterile and surrounds the columella
  • Columella - central cells/region of capsule which are sterile
  • Sporogenous layer - layer in the capsule found between the capsule wall and columella; produces pseudo-elaters and spores
  • Pseudo-elaters - multicellular layer with spiral/helical thickenings that will covers the spores and helps in spore dispersal
  • Spore - found inside the capsule, relatively large about 30-80 um in diameter
  • Protonema - filaments which will grow and form mature gametophyte
• Biflagellate sperms released from the antheridia of a male moss travel along the neck canal to fertilize the single egg cell located inside the venter. Once the egg is fertilized, the zygote that is produced remains in the venter, develops into an embryo and later into a sporophyte
• In the family Polytrichaceae, water conducting cells called hydroids and solute conducting cells called leptoids are present in the medulla