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8/28/2011
Ch 16
Bryophytes
Bryophytes
• Consist of liverworts, hornworts, and
mosses.
• Often grow in moist conditions
– Not
N t relegated
l
t d tto these
th
only
l
• Large constituent of carbon storage
• Sensitive to air pollution
– Often absent in high pollution areas
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Characters
• Characteristics that distinguish bryophytes
from charophytes:
– Male and female gametangia
• Antheridia & archegonia with protective sterile jacket
layer.
– Retention of zygote and embryo (i.e., sporophyte
within the archegonium or the female
gametophyte).
– Multicellular diploid sporophyte
– Multicellular sporangia
– Meiospores containing sporopollenin
– Tissues produced by apical meristem
Structure & Reproduction
• Hornworts & Liverworts described as:
– “thalloid” b/c gametophytes are thalli.
• Not differentiated into roots, leaves, and stems
• Cells are interconnected by
plasmodesmata.
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Bryophyte sperm
• Many bryophytes reproduce asexually– Small pieces of tissue produce an entire
gametophyte
• Liverworts & mosses
– Gemmae
• Multicellular bodies that give rise to new
gametophytes.
Sexual reproduction
• Production of antheridia & archegonia
– On separate male or female gametophytes
– Spherical or elongated antheridium is
commonly stalked
stalked.
• Sterile jacket layer that surrounds numerous
spermatogenous cells.
• ‘jacket’ layer is sterile
– Cannot produce sperm
– Each spermatogenous
cell forms a single
biflagellated sperm that
must swim through
water to reach the egg;
located inside the
archegonium.
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• Venter
– Encloses a single egg
• Neck canal cells
– Disintegrate when the egg is mature which forms
a fluid-filled tube through which the sperm swim
to the egg.
– Chemicals are released that attract sperm.
– Zygote is nourished by sugars, amino acids;
• Known as matrotrophy
• Matrotrophy fuels production of diploid
sporophytes (like the placenta of plants).
Embryophytes (synonym for plants)
• Throughout evolutionary history
sporophytes have become increasingly
larger than gametophyte generation.
• Sporophytes of hornworts & mosses have
stomata
– Bordered by guard cells (which resemble
stomata of vascular cells).
Sporopollenin
• Bryophyte spores are impregnated with
sporopollenin
– Decay & chemical resistant bipolymer
• Spores germinate to form:
1. Protonemata
2. Gametophytes & Gametangia
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Byrophytes: 3 phyla
• Liverworts
– Hepatophyta
• Hornworts
– Anthocerophyta
A th
h t
• Mosses
– Bryophytes
Liverworts: Hepatophyta
• ~ 6,000 spp.
• Small & inconspicuous
• Named ‘liverwort’ because of the liver
shaped
h
d outline
tli off th
the gametophyte
t h t iin
some genera.
• Most gametophytes develop from spores.
– Some form a protonema-like filament of cells
from which a gametophyte develops.
Three major types of liverworts
• Differentiated on basis of structure and
grouped into two clades.
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Complex Thalloid Liverworts
• Riccia, Ricciocarpus, and Marchantia
• Found on moist shaded banks.
• Thallus is 30 cells thick at midrib
– Upper (dorsal) portion is chlorophyll rich
– Lower (ventral) portion bears rhizoids &
scales
Riccia & Ricciocarpus
• Sporophyte structure of these is simplest
seen in liverworts.
• Ricciocarpus grows in water or damp soil
– Bisexual (both sex organs arise on same plant)
– Riccia gametophytes
• Unisexual or bisexual
• Sporophytes are deeply embedded
– Once gametophyte containing sporophytes dies
• Spores are liberated
System of branching
gametophytes in Riccia.
Sporophyte embedded
within the gametophyte.
(spherical capsule)
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Marchantia
•
•
•
•
•
Most familiar liverwort
Gametangia borne on gametophores.
Gametophytes are unisexual
Antheridia borne on antheridiophores.
antheridiophores
Archegonia are borne on
archegoniophores.
• Sproangium contains elaters
– Elongate cells which have helically arranged
hygroscopic wall thickenings.
Archegonia of Marchantia
Antheridia of Marchantia
Mature spores (red) and elaters (green strands)
from a capsule of Marchantia.
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Marchantia reproduction
• Fragmentation is principle asexual method
• Another widespread mechanism
– Production of gemmae
• In Marchantia the gemmae are produced
in cuplike structures
– Gemmae cups
• Gemmae are dispersed primarily by
splashed of rain.
Marchantia gametophytes.
Gemmae cups containing gemmae.
Longitudinal section
of gemmae cup
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Leafy liverworts
• 4,000 of the 6,000 species in phylum
hepatophyta.
• Abundant in tropics & sub-tropics
• Leaves
L
consist
i t off single
i l llayer off
undifferentiated cells.
• Two rows of equal sized leaves & third row
of smaller leaves along lower surface of
gametophyte.
• Antheridia generally occur on short side
branch with modified leaves called:
– Androecium
• Archegonium & developing sporophyte
surrounded by:
– Perianth
Gametophyte with
attached sporophytes
Sporangium
p
g
splits, and
spores released
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Hornworts: Anthocerophyta
• 100 spp.
• Anthoceros is most abundant
• Hornwort gametophytes superficially
resemble
bl those
th
off thallose
th ll
li
liverworts.
t
• Gametophytes are often rosette-like
– Most are unisexual
• Sporophytes of Anthoceros
– Have foot & long capsule (sporangium)
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Mosses: Bryophyta
• Consists of three classes
– Sphagnidae, Andreaeidae, & Bryidae
• Bryidae 9,500 spp.
Peat Mosses: Sphagnidae
• One large genus
– Sphagnum
– 400 spp
• Distributed
Di t ib t d worldwide
ld id
– Commercially & Economically important
Sexual Reproduction
• Formation of antheridia & archegonia
– Occurs at ends of special branches at the tips
of the gametophyte.
– Fertilization occurs in late winter
• Four months later, mature spores are discharged
from sporangia.
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• Gametophyte
with many
attached
sporophytes.
Dehiscence has
occurred
Capsule dries &
contracts
Explosion of
spores
Compression of
trapped gas
Features that distinguish
Sphagnidae from other mosses
• Unusual
protonema
Leafy gametophyte
• Peculiar
morphology of
gametophyte
• Explosive
operculum
Plate-like protonema
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Sundberg 2010: Annals of Botany 105: 291-300
• Sphagnum has superior antiseptic &
absorptive properties.
– Used as diaper material by native peoples
and in WWI as dressings for wounds
wounds.
Worldwide importance
• Peatlands occupy > 1 % of earth’s surface.
Area of peatland (KM sq)
% peatland
Africa
58,534
0.18
Asia
1,523,287
1.06
Australia, New Zealand, the
Pacific and Antartica
8,009
0.04
North, Central and South
America
2,050,746
4.83
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http://www.ramsar.org/pictures/types-peat-nz-waituna350.jpg
http://www.google.com/imgres?q=close+up+of+peat&hl=en&client=firefox-a&hs=I8k&sa=X&rls=org.mozilla:enUS:official&biw=1680&bih=944&tbm=isch&prmd=ivns&tbnid=16E2Iev2P00mM:&imgrefurl=http://www.flickr.com/photos/newtosandiego/4536278778/&docid=mb6fzlMgeqAu8M&w=500&h=332&ei=_v1LT
sDhCY2EsgL87PHHCA&zoom=1
• Store large amounts of organic carbon
– 400 gigatons (400,000,000,000)
• Global warming may result in oxidation of
peatland carbon:
– Further increasing CO2 levels and global
temperatures
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Granite mosses: Andreaeidae
• Two genera:
– Andreaea & Andreaeobryum
• Andreaea consists of 100 spp.
– Mountainous
M
t i
& arctic
ti regions
i
((often
ft on granite
it
rocks)
• Andreaeobryum single species
– Northwestern Canada & Alaska
– Grows on calcareous rocks
http://www.teara.govt.nz/files/p10768au.jpg
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“True Mosses”: Bryidae
• Branching filaments of protonemata have
single row of cells & resemble filamentous
green algae:
– Mosses have slanted cross walls
walls.
Specialized tissues for water &
food conduction
• Stems of gametophytes &
sporophytes have central
strand of waterconducting tissue
– Hadrom
• Water-conducting cells
– Hydroids
• Food conducting
cells
– Leptoids
• Food conducting
tissue
– leptom
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Moss sexual reproduction
• Similar to horn & liverworts
– Male & female gametangia
– Unbranched matrotrophic sporophyte
– Specialized spore dispersal process
• Gametangia produced by leafy
gametophytes.
– Unisexual or bisexual
– Sperm from antheridia discharged into a drop
of water in splash cups.
– Insects may also carry drops of water rich in
sperm from plant to plant.
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• Sporophytes are borne on gametophytes
– Capsules take 6 to 18 mo. to mature
– Sporophyte cells contain chloroplasts
• Conduct photosynthesis
• As
A ages loses
l
ability
bilit tto photosynthesize
h t
th i
• Spore dispersal results from bursting of
operculum
– Reveals a ring of teeth known as peristome
• Asexual reproduction occurs by
fragmentation.
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Growth patterns of moss
• Two forms
– Cushiony (gametophytes are erect & a little
branched- terminal sporophytes)
– Feathery (highly branched; sporophytes are
borne laterally).
• Feathery growth is found on mosses that
hang from branches:
– Referred to as epiphytes
http://2.bp.blogspot.com/_JHKjXsX0KEk/SRd77opai1I/AAAAAAAACQE/bqmz8Q984mE/s1600/moss-laden%2Btrees.jpg
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Summary
• Embryophytes evolved from Charophytes.
• Bryophytes: Liverworts, Hornworts, &
Mosses
• Bryophytes
B
h t differ
diff from
f
one another
th by
b the
th
presence/absence of stomata &
conducting tissues & types of meristems.
• Ecologically important
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