Bryophytes:
Mosses and Relatives
Bryophytes
The term “Bryophyte” is not a
strict taxonomic category. It
includes the mosses and mosslike relatives (liverworts and
hornworts).
Bryology – the study of moss and
moss-like relatives.
Byrophytes – a group of small,
mainly terrestrial plants that
have an embryo life cycle phase
but lack vascular tissue;
contains mosses, liverworts
and hornworts.
Bryophytes are arguably the most
primitive plants in the Plant
Kingdom. They are the first
land plants to arise.
In variable climates, bryophytes
are dormant much of the year.
Epiphytic mosses on trees.
Bryophyte Facts
- 25,000 named bryophyte species.
- Extremely widespread (Extreme cold to very hot), being present on all
continents. This includes Antarctica.
- No lignin present. Remember that lignin is found in many plant cell
walls, provides strength for wood and it is necessary in support of tall
plants. Therefore, bryophytes are small.
- No Vascular (Xylem/Phloem) Tissue. Therefore, bryophytes absorb
water by diffusion. They are often restricted to moist habitats.
Mosses are the green,
carpet-like plant seen
growing in damp forests,
sometimes on fallen logs.
A Cladogram or Relationships Between the Bryophytes
& the Vascular Plants.
Bryophyte Divisions
Division Bryophyta
Division Marchantiophyta
Division Anthocerotophyta
Stomata and Cuticle
(protective layer) first
appear in bryophytes.
Cuticle doesn’t cover entire
bryophyte because they
absorb much water and
minerals through their
dermal layer.
Bryophytes
appeared
around 475
million years
ago.
The Gametophyte Dominates the Life Cycle
If you remember from the life cycles
chapter, the gametophyte is the
gamete producing plant. It is n
(haploid) and it produces and holds
the gametes. The sporophyte is the
2n (diploid) plant body.
Like all plants, bryophytes exhibit
alternation of generations. In
bryophytes, the gametophyte
(multicellular) is dominant and
persists for most of the plant’s life.
The sporophyte (multicellular) is
short-lived. It grows from an embryo
embedded within the mature
gametophyte plant and is dependent
on the gametophyte for its nutrition.
The unbranched sporophyte
produces a single sporangium.
The moss,
Mnium,
showing both
sporophyte &
gametophyte
generations.
Gametangia and gametes can be embedded in the gametophyte tissue
as shown here, or attached at the surface of the gametophyte.
Gametangia –
organs that
produce
gametes.
Archegonium (Egg-bearing Organ) with a
long neck extends beyond the venter,
capped at the tip with cover cells.
Note: Unlike algal ancestors, bryophytes
have multicellular gametangia.
Antheridium (Sperm-bearing Organ) with
an outer row of sterile (nonspermforming) cells enclosing inner fertile cells,
each of which becomes a sperm gamete.
General Bryophyte Life Cycle Description
A haploid (n) spore settles on the moist ground, germinates
and develops by mitosis into a threadlike, haploid
protonema (early gametophyte stage) from which
individual gametophytes arise like branches. The
gametophyte derives its nutrients from photosynthesis.
Archegonia and antheridia, structures that produce eggs
and sperm, respectively, develop on the tips of the
gametophyte. The zygote (2n) develops into the
sporophyte, a diploid adult, which is a filament that
grows out of the top of the gametophyte. Out of the tip
of the mature sporophyte sprouts sporangia (Singular,
Sporanguim). Sporangia are where spores are made. In
sporangia, meiosis occurs, producing haploid spores
and the entire life cycle begins again. See Next Slide.
Water is very important in fertilization. Sperm (flagellated)
must swim through water to fertilize an egg.
Life Cycle of
Polytrichum, a typical moss.
Hornworts
Division Anthocerotophyta
Hornworts often have
long, pointed
sporophytes (resembling
horns) that rise from the
thalloid gametophytes.
Liverworts
Division Marchantiophyta
Liverworts look like liver. They were used as medicine to
help the liver in the middle ages in Europe because of this.
Mosses
Division Bryophyta
Bryophyta includes
the most bryophyte
species. This
division includes the
true mosses, granite
mosses and peat
mosses. The
Sphagnum genus is
an important peat
moss. It is used in
potting soil for better
water-holding
capabilities.
Gametangia of Mnium, a moss that produces
antheridia and archegonia on different heads
but on the same plant.
Bryophyte Ecology and Human Use
Bryophyte gametophytes are not able to control their water balance and they
dry out rapidly in the absence of free water but some can be drought resistant
and come back and thrive with water.
Bryophytes play a significant role in diverse terrestrial ecosystems. They grow
on soil, rocks and trees. Wetland moss, sphagnum or peat moss is especially
widespread, forming deposits of peat, commonly used as fuel in much of the
world. In addition to its role as a fuel, peat moss is added to soil to enable it to
retain moisture or as a packing material for transporting plant roots.
Bryophytes are very important in
many ecosystems and moss
makes up much of the biomass in
boreal tundra vegetation.
Bryophytes often dominate
understory vegetation in cool
temperate (not too hot/not too
cold) forests. Most cool
microenvironments have
bryophytes. Some bryophyte
species can colonize dry areas.
BIO 141 Botany with Laboratory
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