3. Bryophyte, traditional name for any nonvascular seedless
plant—namely, any of the mosses (division
Bryophyta), hornworts (division Anthocerotophyta),
and liverworts (division Marchantiophyta). Most bryophytes
lack complex tissue organization, yet they show
considerable diversity in form and ecology. The first evidence
marking the emergence of bryophytes appears in rocks
collected from Argentina that date to the early part of
the Ordovician Period (485.4 million to 443.8 million years
ago).
Habit- Bryophytes often grow profusely, forming deep, soft
carpets on forest floors and over rock surfaces, sheathing
trunks and branches of trees and shrubs, and festooning
branches.
5. Distribution and abundance
Bryophytes are distributed throughout the world, from polar
and alpine regions to the tropics. Water must, at some point, be
present in the habitat in order for the sperm to swim to the egg.
Bryophytes do not live in extremely arid sites or in seawater,
although some are found in perennially
damp environments within arid regions and a few are found on
seashores above the intertidal zone. A few bryophytes are
aquatic. Bryophytes are most abundant in climates that are
constantly humid and equable. The greatest diversity is at
tropical and subtropical latitudes. Bryophytes (especially
the moss Sphagnum) dominate the vegetation of peatland in
extensive areas of the cooler parts of the Northern
Hemisphere.
6. General Features- Some liverworts and hornworts have a
flattened gametophyte, called a thallus. The thallus tends to be
ribbonlike in form and is often compressed against the
substratum to which it is generally attached by threadlike
structures called rhizoids. Rhizoids also influence water and
mineral uptake.
Thallus bryophytes vary in size from a length of 20 cm (8 inches) and a
breadth of 5 cm (2 inches; the liverwort Monoclea) to less than 1 mm
(0.04 inch) in width and less than 1 mm in length (male plants of the
liverwort Sphaerocarpos). The thallus is sometimes one cell layer thick
through most of its width (e.g., the liverwort Metzgeria) but may be
many cell layers thick and have a complex tissue organization (e.g., the
liverwort Marchantia). Branching of the thallus may be forked, regularly
frondlike, digitate, or completely irregular. The margin of the thallus is
often smooth but is sometimes toothed; it may be ruffled, flat, or curved
inward or downward.
7.
8. Leafy bryophytes grow up to 65 cm (2 feet) in height
(the moss Dawsonia) or, if reclining, reach lengths of more than 1 metre
(3.3 feet; the moss Fontinalis). They are generally less than 3 to 6 cm
(1.2 to 2.4 inches) tall, and reclining forms are usually less than 2 cm
(0.8 inch) long. Some, however, are less than 1 mm in size (the
moss Ephemerum). Leaf like structures, known as phyllids, are arranged
in rows of two or three or more around a shoot or may be irregularly
arranged (e.g., the liverwort Takakia). The shoot may or may not appear
flattened. The phyllids are usually attached by an expanded base and are
mainly one cell thick. Many mosses, however, possess one or more
midribs several cells in thickness. The phyllids of bryophytes generally
lack vascular tissue and are thus not analogous to the true leaves of
vascular plants.
9. Most gametophytes are green, and all except the gametophyte
of the liverwort Cryptothallus have chlorophyll. Many have
other pigments, especially in the cellulosic cell walls but
sometimes within the cytoplasm of the cells.
Bryophytes form flattened mats, spongy carpets, turfs, or
festooning pendants. These growth forms are usually
correlated with the humidity and sunlight available in the
habitat. The thalli of most liverworts and hornworts consist of
relatively undifferentiated layers of cells. Those cells on the
dorsal surface are rich in chlorophyll, while those situated
deeper within the thallus lack chlorophyll but have storage
products of photosynthesis, especially starch.
10. Reproduction and life cycle
The life cycle of bryophytes consists of an alternation of two
stages, or generations, called the sporophyte and
the gametophyte. Each generation has a different physical
form. When a spore germinates, it usually produces the
protonema, which precedes the appearance of the more
elaborately organized gametophytic plant, the gametophyte,
which produces the sex organs. The protonema is usually
threadlike and is highly branched in the mosses but is reduced
to only a few cells in most liverworts and hornworts. The
protonema stage in liverworts is usually called a sporeling in
other bryophytes.
11. Vegetative Reproduction-The gametophyte of some bryophyte
species reproduces asexually, or vegetatively, by specialized
masses of cells (gemmae) that are usually budded off and
ultimately give rise to gametophytes. Fragmentation of the
gametophyte also results in vegetative reproduction: each
living fragment has the potential to grow into a complete
gametophyte.
Fragmentation
Gemmae
12. Asexual reproduction-Sporophytes of mosses usually consist
of the foot, which penetrates the gametophore, the seta, with
an internal conducting system, and a terminal sporangium. The
seta contains chlorophyll when immature and cannot absorb
moisture from the environment because its surface is covered
by a water-impermeable layer, the cuticle. The sporophyte is
photosynthetic when immature, but its restricted amount of
chlorophyll-containing tissue rarely produces enough
carbohydrates to nourish a developing sporangium. All water
and much of the needed nutrients are absorbed from the
gametophore and are conducted through the transfer tissue of
the foot up the conducting strand that leads to the apex of the
sporophyte. The seta is made rigid by thick-walled cells
external to the conducting strand.
The sporangium differentiates after the seta elongates and is
protected from injury and drying by the calyptra.
13. The moss sporangium usually opens by way of an apical lid
(the operculum). When the operculum falls, there is exposed a
ring of teeth that controls the release of the spores over an
extended period of time. These teeth usually respond to slight
moisture changes and pulsate inward and outward, carrying
spores out of the sporangium on their jagged inner surfaces.
The sporangium usually contains within it elongate cells
(elaters) with coiled thickenings that are scattered among the
spores.
14.
15. Sexual Reproduction-
The gametophyte—the thallus or leafy stage—is
generally perennial and produces the male or female sex
organs or both. The female sex organ is usually a flask-shaped
structure called the archegonium. The archegonium contains a
single egg enclosed in a swollen lower portion that is more
than one cell thick. The neck of the archegonium is a single
cell layer thick and sheathes a single thread of cells that forms
the neck canal. When mature and completely moist, the neck
canal cells of the archegonium disintegrate, releasing a column
of fluid to the neck canal and the surrounding water. The egg
remains in the base of the archegonium, ready for fertilization.
The male sex organ, the antheridium, is a saclike structure
made up of a jacket of sterile cells one cell thick; it encloses
many cells, each of which, when mature, produces one sperm.
16. The antheridium is usually attached to the gametophyte by a
slender stalk. When wet, the jacket of the mature antheridium
ruptures to release the sperm into the water. Each sperm has
two flagella and swims in a corkscrew pattern. When a sperm
enters the field of the fluid diffused from the neck canal, it
swims toward the site of greatest concentration of this fluid,
therefore down the neck canal to the egg. Upon reaching the
egg, the sperm burrows into its wall, and the egg nucleus
unites with the sperm nucleus to produce the diploid zygote.
The zygote remains in the archegonium and undergoes
many mitotic cell divisions to produce an embryonic
sporophyte. The lower cells of the archegonium also divide
and produce a protective structure, called the calyptra, that
sheathes the growing embryo.
17.
18. As the sporophyte enlarges, it is dependent on the
gametophore for water and minerals and, to a large
degree, for nutrients manufactured by the
gametophyte. The water and nutrients enter the
developing sporophyte through the tissue at its base, or
foot, which remains embedded in the gametophyte.
Mature bryophytes have a single sporangium (spore-
producing structure) on each sporophyte. The
sporangium generally terminates an elongate stalk, or
seta, when the sporangium is ready to shed its spores.
The sporangium rupture usually involves specialized
structures that enhance expulsion of the spores away
from the parent gametophyte.
19. Alternation of generations- The bryophytes show
an alternation of generations between the
independent gametophyte generation, which produces the sex
organs and sperm and eggs, and the
dependent sporophyte generation, which produces the spores.
(produces only one spore-containing organ ,sporangium). In
bryophytes the long-lived and conspicuous generation is the
gametophyte. Structures resembling stems, roots, and leaves
are found on the gametophore of bryophytes. The sporophyte
releases spores, from which the gametophytes ultimately
develop.
20.
21. Economic importance-
1.The peat moss genus Sphagnum used in horticulture,
as an energy source (fuel), and, to a limited extent,
in the extraction of organic products, in whiskey
production, and as insulation.
2. Bryophytes are very important in initiating soil
formation on barren terrain, in maintaining soil
moisture, and in recycling nutrients in forest
vegetation.
3. In research- in areas of genetics and cytology.
23. Division Bryophyta
Class 3.
Musci (mosses)/Bray
opsida
Subclass1.Sphagnidae
Order1- Sphagnales
Subclass2.Andreaeidae
Order 1- Andreaeales
Subclass 3.Bryidae
Order1- Polytrichales
Order2- Funariales
Class2. Anthocerotae (horn
worts)/Anthoceropsida
Class 1.
Hepaticae (liverworts)/Hepa
ticopsida
Order 1. Sphaerocarpales
Family 1. Sphaerocarpaceae
Family 2. Riellaceae
Order 2. Marchantiales
Family 1. Ricciaceae
Family 2. Corsiniaceae
Family 3. Targioniaceae
Family 4. Monocleaceae
Family 5. Marchantiaceae
Order 3. Jungermanniales
Suborder 1. Metzgerineae
Suborder 2. Jungermannineae
Order 4. Calobryales
Order 1-Anthocerotales
24. Hepaticae: A class of Bryophyta comprising the liverworts and being
distinguished from Musci by the presence of a usually thalloid
gametophyte that is not produced from a protonema, unicellular
rhizoids and elaters and antheridia and archegonia that are borne on
the thallus and produce a short-lived and simple sporophyte.
Anthocerotae: The Anthocerotae (hornworts) is one class of the
Division Bryophyta (bryophytes) and consists of a single
order, Anthocerotales, and a single family, Anthocerotaceae. The
better known classes of the Bryophyta are the Musci (mosses) and
Hepaticae (liverworts).
Musci : A class of Bryophyta comprising the mosses and being
characterized by a well-developed leafy gametophyte that arises by
budding from a protonema and bears sex organs among the leaves at its
tip and by a sporophyte that develops from the fertilized egg, remains
attached to the tip of the gametophyte, and is a naked usually stalked and
operculate capsule in which asexual spores are borne.
25. Class I- Hepaticae/ Hepaticopsida (Liverworts)
(4 orders, 9 families, 225 genera and 8,500+- species)
1. The gametophytes are dorosiventrally differentiated. They may be thalloid
(thallose) or differentiated into leaves and stem (foliose).
2. Leaves, if present, are without mid-rib and are arranged into two or tghree
rows on the axis.
3. The dehiscent mechanism of capsules is indefinite and irregular.
4. The sporophyte may be simple, or differentiated into foot and capsule, or into
a foot seta and capsule,
5. The sporogenous cells develop from the endothecium of sporogonium.
6. The sporophyte is completely dependent on gametophytes for its nutritive
supply.
7. The wall of sporogonium is one to several layered thick. The stomata are not
present on the wall of sporogonium.
Order - Sphaerocarpales (3 genera and 2 families)
Order – Marchantiales (32 genera and 400 species)
Order – Jungermanniales (220 genera and 8,500 species)
Order – Calobryales (2 genera and 9 species)
26. Class II- Anthocerotae/ Anthocerotopsida (Hornworts):
(1 orders, 2 families, 6 genera and 301+- species)
1. The gametophyte is thalloid and dorsiventral, bearing
simple and smooth-walled rhizoides; tuberculate
rhizoids and ventral scales are altogether absent.
2. Thallus is homogenous internally.
3. Each cell of the thallus is provuded with a hloroplast, a
nucleus and a pyrenoid body. Pyrenoid body includes
several granules.
4. The wall of capsule is 4-6 layers of cells thick, and is
provided with stomata.
5. The basal portion of capsule is meristematic. It divides
continuously to add to the upper portion.
27. 6. The sex organs are found to be embedded in the
gametophytic tissue.
7. Sporogenous mass evolve form amphithecium and
arches over the columella.
8. The antheridia arise from the hypodermal cell of the
thallus on the dorsal side of it; they develop within the
antheridial chambers.
9. The archegonia are found in sunken conditions on the
dorsal side of the thallus, they develop from superficial
cells.
Family – Anthocerotaceae (4/5 genera)
Family – Notothylaceae (Single genus – Notothylas)
28. Class III – Musci/ Bryopsida (Mosses):
(3 orders, 28 families, 660 genera and 14504+- species)
1. The plants have well differentiated structures including axis,
leaves and multicellular rhizoids.
2. The leaves are arranged in 3-8 rows on the axis. Each leaf has a
mid-rib.
3. The wall of the capsule consists of many layers of chlorophyllous
cells and stomata.
4. sex organs develop on apical portion of stem.
5. The sporophyte is differentiated into foot, seta and capsule.
6. The sporogenous mass or archesporium develops from the outer
layer of endothecium. Endothecium also forms columella.
7. The eleters are not present in the sporogonium
29. Sub-class I – Sphagnidae/ Spagnobrya
(1 order, 1 family, 1 genus Sphagnum, 326 species)
Order1- Sphagnales
Sub-class II – Andreaeidae/ Andreaeobrya (1 order, 1 family)
Order 1- Andreaeales
Sub-class III – Bryidae/ Eubrya (650 genera, 14,000 species)
Order I – Polytrichales (1 family, important genera – Polytrichum &
Pogonatum)
Order II – Funariales (26 genera and 356 species)
