Definition: Bryophytes are informal names for mosses, liverworts, or hornworts; they are non-vascular plants that live on land but lack some terrestrial adaptations of vascular plants.
Phylogeny:
Bryophytes diverged earliest from the common ancestor of land plants and form a paraphyletic group of three small non-vascular plant phyla.
Known as herbaceous plants.
Reference: Campbell biology, 4th Canadian ed. (2024).
Characteristics of Bryophytes
Absence of true vascular tissue and lignin: Limits size due to lack of structural support and a complex nutrient transportation system.
Absence of true roots: Water absorption through surface rhizoids.
Habitat: Require water-rich environments.
Structure:
Rhizoids in liverworts and leaves in mosses.
Unbranched sporophytes; stoma absent in liverworts but present in mosses and hornworts.
Life Cycle:
Gametophytes (1n) are larger and longer-living than sporophytes (2n).
Sporophytes depend on gametophytes for nutrients and remain physically attached.
Life Cycle of Bryophytes
Hornwort Anthoceros agrestis: Establishment as a model species for hornwort biology.
Moss Life Cycle:
Gametophytes Stage:
Haploid spores released, germinate into gametophytes composed of protonema and gametophore.
Gametophytes mature into male and female, producing gametangia (sperms and eggs).
Fertilization requires water for sperm to swim to the egg.
Sporophytes Stage:
Development from fertilized zygote to a diploid embryo and sporophyte.
Sporophyte matures, develops a sporangium where meiosis creates spores.
Spores are released and dispersed, beginning asexual reproduction phase.
Major Groups of Bryophytes
Liverworts (phylum Hepatophyta):
~9,000 extant species, no xylem/phloem, no stoma, contains oil bodies.
Ecological role: Soil stabilization, antimicrobial and antifungal properties.
Mosses (phylum Bryophyta):
~15,000 extant species, no xylem/phloem, has stomata.
Ecological role: Water retention, soil conditioning with peat moss.
Hornworts (phylum Anthocerophyta):
~100 extant species, single large chloroplast, lacks seta.
Ecological role: Symbiotic relationships with cyanobacteria.
Reflective Questions
How do shared characteristics position bryophytes on a phylogenetic tree leading to vascular plants?
Can you describe a typical life cycle of bryophytes?
How can we distinguish the main groups of bryophytes?