Rucete ✏ Campbell Biology In a Nutshell
Unit 5 THE EVOLUTIONARY HISTORY OF BIOLOGICAL DIVERSITY — Concept 29.2 Mosses and Other Nonvascular Plants Have Life Cycles Dominated by Gametophytes
Bryophytes—liverworts, mosses, and hornworts—are nonvascular plants with life cycles dominated by haploid gametophytes. These plants were among the first to colonize land and exhibit many adaptations that allow them to reproduce and survive in moist environments.
Bryophyte Phyla and Life Cycle Dominance
- Three phyla:
- Liverworts (Hepatophyta)
- Mosses (Bryophyta)
- Hornworts (Anthocerophyta)
- Gametophyte-dominant life cycle:
- Gametophytes are larger and longer-living than sporophytes
- Gametangia produce gametes:
- Archegonia (female): one egg each
- Antheridia (male): many flagellated sperm
- Fertilization requires water; sperm swim to egg
- Sporophytes remain attached to and dependent on gametophytes
Key Features of Bryophyte Reproduction
- Spores germinate into protonemata, which form buds
- Buds develop into mature gametophytes
- Sporophyte grows from zygote:
- Foot: absorbs nutrients
- Seta: stalk supporting sporangium
- Capsule (sporangium): produces spores via meiosis
- Peristome teeth in mosses regulate spore dispersal
Structural Adaptations and Growth Limitations
- Rhizoids anchor gametophytes (not true roots)
- Low-growing due to:
- Lack of vascular tissue
- Thin tissues restrict transport distances
- Some mosses grow up to 60 cm using rudimentary conducting tissues
Asexual Reproduction and Survival Strategies
- Brood bodies: small plantlets that grow into clones
- Desiccation tolerance: dormant state until water returns
- Phenolic compounds resist UV and decay
Ecological and Global Significance of Mosses
- Live in forests, wetlands, deserts, and tundra
- Polytrichum: helps retain soil nitrogen
- Pleurozium: supports nitrogen-fixing cyanobacteria
- Sphagnum (peat moss) forms peatlands:
- Stores ~500 billion tons of organic carbon
- Slow decomposition due to acidity and low oxygen
- Used as fuel, soil additive, and packaging
- Helps cool global climate but threatened by warming and harvest
In a Nutshell
Bryophytes are the earliest land plants and still thrive in moist habitats. Their gametophyte-dominant life cycle, simple body structure, and reliance on water for fertilization reflect their evolutionary origins. Ecologically, they retain nutrients, host nitrogen fixers, and store massive amounts of carbon—making them small but mighty players in Earth’s ecosystems.