27 Bryophytes

Learning Objectives

  • Identify main characteristics of bryophytes

  • Describe and distinguish traits of liverworts, hornworts, and mosses

  • Chart the development of land adaptations in bryophytes

  • Describe events of the bryophyte lifecycle

Bryophytes

  • Closest extant relatives of early terrestrial plants (approximately 450 million years ago)

  • Diversity: 25,000 species identified to date

  • Habitat: Thrive in tundra and other moist environments

  • Structure: Lack xylem and lignin, resulting in no fossil records

  • Nutrient Circulation: Water and nutrients circulate via specialized conducting cells

  • Life Cycle Dominance: Dominated by the gametophyte stage (haploid, n)

    • Male Gamete: Possesses flagella

    • Sporophyte: Dependent on gametophyte; sporangium is barely visible

Liverworts (Hepaticophyta)

  • Relation: Most closely related to the ancestor of terrestrial vascular plants

  • Diversity: About 7,000 species

  • Morphology: Characterized by a lobe-like flat thallus (some are leafy)

  • Gas Exchange: Organelles facilitate gas movement (lack of stomata)

  • Sporophyte Structure: Contained within an archegonium (refer to figure 25.11)

  • Reproduction: Asexual reproduction occurs through fragmentation

Hornworts (Anthocerophyta)

  • Morphology: Have narrow pipe-like sporophytes

  • Sporophyte Development: Emerges from the gametophyte

  • Stomata Presence: First appearance of stomata in this group

  • Symbiotic Relationships: Many species have symbiotic associations with cyanobacteria

  • Life Cycle: Follows an alternation of generations pattern (refer to figure 25.13)

Mosses

  • Diversity: More than 10,000 species

  • Habitat: Extremely abundant in tundra and bogs

  • Sensitivity: Sensitive to air pollution and copper (Cu) salts

  • Life Cycle Dominance: Gametophyte stage dominates the life cycle (refer to figure 25.14)

  • Structure: Lack stomata and vascular tissue

  • Anchoring: Anchored to substrate using rhizoids

    • Water Absorption: Not a major route for water absorption

  • Sporophyte Connection: Sporophyte remains attached to the gametophyte (refer to figure 25.15)