Botany 10
Dr. Bibit Traut
Lecture: Bryophytes
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Bryophytes
Common name applied to three distinct lineages of plants that lack
lignified vascular tissue
Three lineages
• Liverworts
• Hornworts
• Mosses
Plant Ancestors
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Plants probably evolved from green algae charophytes
Evidence:
• pigments (chlorophylls a and b, carotenes, xanthophylls)
• cell-wall components (cellulose)
• carbohydrate storage material (starch)
• molecular data
Li f e o n L a n d
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Problems:
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dessication
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avoiding damage from weather & solar radiation
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dispersing spores in air
Solutions:
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Cuticle (stomata allows for gas exchange)
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Protection of sporophyte by gametophytes
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protects spores from dessication
Coated with weather-resistant wall
Multicellular gametangia surrounding & protecting gametes
The Gametophyte Generation
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Produces haploid gametes by mitosis
• Antheridium produces sperm cells
• Archegonium produces an egg
Fertilization: Gametes fuse to form a diploid zygote
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Botany 10
Dr. Bibit Traut
The Sporophyte Generation
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First stage is zygote
• Develops into an embryo, protected and nourished by
gametophyte plant
Mature sporophyte plant has sporocytes that undergo meiosis to
produce haploid spores
• First stage in gametophyte generation
Bryophytes
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Small, fairly simple plants
• Body referred to as “thallus” (lack leaves, roots, stems)
Nonvascular
Gametophyte is dominant generation
• grows independently of sporophyte and is usually perennial
Hepatophyta “liverworts”
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Approximately 9,000 species
Gametophyte generation is dominant phase of life cycle
Usually grow in moist, shady habitats
Gametophytes
• produce volatile oils
• rhizoids
• pores on upper surface
• body form
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thallose types
Leafy types
Sporophytes
• Simple
• Capsule splits into 4 valves & releases spores at once
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Botany 10
Dr. Bibit Traut
Liverwort Reproduction
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Thallose liverworts
• asexually by:
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Gemmae
Sexually by:
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Fragmentation
Antheridiophores “umbrellas”
Archegoniophores “palm trees”
Sporophytes develop under archegonia
Life Cycle: Liverworts
Anthocerophyta “hornworts”
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Gametophytes
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produce mucilage inside thallus
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Ventral portion of thallus has pores (forms symbiotic colonies with
Nostoc)
Unique sporophyte
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Grows continually from basal meristem
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stomata
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Foot with upright sporangium
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produce 1n spores by meiosis
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Sterile tissue in center of sporangium (columella)
Bryophyta “mosses”
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Larger & more widely distributed than liverworts & hornworts
Grow in many environments:
• on rocks in cool climates
• in acidic bogs
• on soil
• on other plants, wood
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Botany 10
Dr. Bibit Traut
Moss Gametophytes
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Dominant
each protonema can produce many leafy gametophytes
stomata
thin cuticle
epidermal cells store water
Stem-like thallus may have central strand of conducting tissue
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Hydroids (like vessels)
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Leptoids (like sieve cells)
Moss Asexual Reproduction
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Protonema produce new buds
Leafy tissue placed in wet soil produce protonemal strands
Rhizoids produce buds
Moss Sexual Reproduction
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Gametangia produced at stem-like thallus tips
• separated & held upright by sterile filaments
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Antheridia: release mature sperm when water present
Archegonium: Thickened region surrounds egg; Egg emits
chemical attractant
Sporophyte
• Zygote develops into sporophyte that has a sporangia
• Spores (by meiosis)
Mosses Ecological Role
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Colonize rock previously colonized by lichens
• Help form thin soil in which grasses and other plants can grow
Grow in dense colonies
• Hold soil in place, help prevent soil erosion
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