Department of Botany, Girraj Govt. College: BRYOPHYTA

Bryophytes are primitive plants. They occupy intermediate position between

Algae and Pteridophytes. Bryophytes are amphibians of the kingdom plantae.

Plants grow in two well-defined habitats. These are the water and the land.

Between these two extremes of habitats is a transitional zone. It is represented

by swamps and the areas where water and land meet. It may well be called the

amphibious zone.

Inhabiting the amphibious zone are the mosses, Liverworts and hornworts which

collectively constitute a group of non-vascular land plants called the Bryophytes.

Jussieu (1836) for the first time used the word ‘Mosses’ to represent this group of plants.

Braun (1864) introuduced the name “Bryophyta’ and included Algae, Fungi, Lichen and

Mosses in it. Schimper (1879) gave the rank of a division to Bryophyta and now it

includes Liverworts, Hornworts and Mosses.

The term Bryophyta is derived from two Greek words ‘Bryon’ meaning moss and

‘Phyton’ meaning plants. The branch of botany that deals with Bryophytes is known

and Bryology. Prof. Sivaram Kashyap has studied the Himalayan Bryophytes

extensively and is known as Father of Indian Bryology.

Bryophytes are represented by 960 genera and 25,000 species. They are simplest and

most primitive terrestrial plants. They are world-wide in distribution and occur in all

climates, wherever there is enough moisture to sustain plant life.

Bryophytes are cosmopolitan in distribution. They are found in all places except the sea.
Bryophytes usually grow in moist and shady places. On the sides of ditches, ponds, pools,
lakes, on the banks of streams, damp soil, moist rocks, wet hills etc.

A few of them, however, live in or float on water. Riccia fluitans, Ricciocarpus natans

and Riella areaquatic.The aquatic habit, of course, has been acquired by these plants secondarily. When the water dries up they grow equally well on the drying mud.

Spagnum gorws in bogs; Polytrichum and some other mosses grow in Xeric conditions.
Dendroceros grows as an epiphyte; Radula protensa as epiphyllous and Buxaumia and
Cryptothallus are saprophytic are saprophytic species.

The bryophytes, however, cannot carry on their reproductive activities without sufficient
moisture. Presence of water is necessary. Without it the sex organs do not reach maturity
and do not dehisce.
Water is essential for the transfer of sperms to the archegonium. The retention of
swimming sperms is an algal characteristic. The bryophytes thus rely on water for the
act of fertilization.

This explains why the bryophytes usually inhabit moist, shaded situations or grow
in places where water is abundant at least at some season. Since the bryophytes usually
grow in amphibious situations and cannot complete their life cycle without external
water they can very appropriately be called the amphibians of the plant world.

LIFE CYCLE

The bryophytes have evolved a life cycle which comprises two phases – gametophyte and
sporophyte.
The dominant and most conspicuous plant body, is a gametophyte. It is independent

and autotrophic plant.
It is haploid and represents sexual generation. It bears sex organs – antheridia and archegonia
– and produces gametes : antherozoids and egg.

The fertilization of an egg with an antherozoid (syngamy) results in the formation

of an embryo – the diploid or sporophyte generation. The sporophyte undergoes meiosis

to form haploid spores.

One of the main features of bryophyte life cycle is heteromorphic alternation of
generation. The two generations-gametophyte and sporophyte-are not only different in
function but also different in their morphology.

A characteristic of the group is the independent and autotrophic gametophyte generation to
which is always attached the sporophyte generation. The sporophyte is always dependent
on the gametophyte.

GAMETOPHYTE

The gametophyte is most conspicuous phase in the life cycle of the bryophytes. It is dominate,
haploid and mainly concerned with the production of gametes. The gametophytic plant
body is independent, green and long lived.

The plants is relatively small, varying in size and form. In size they range from 16th of an
inch (e.g.,Zoopsis argentia) to about 24 inches (e.g., Dawsonia superba) . It is compact and
better protected against desiccation.

In lower forms( Hepaticopsida), the plant body is relatively simple and has an algal like

thallus. It grows prostrate on the ground. It is attached to the substratum by delicate,

unicellular, hair-like organs called the rhizoids.

The majority of the bryophytes (Anthocerotopsida and Bryopsida), however,
have the plant body differentiated into stem and leaves. The leafy gametophyte of the
liverworts is dorsiventral but in the mosses it is erect.
The erect, leafy moss gametophyte has a stem-like central axis which bears leaf-like
appendanges.
It is fixed to the substratum by means of branched, multicellular rhizoids apparently
resembling the roots.

The rhizoids of the bryophytes, are however, not homologous with those of the higher plants.
They lack the vascular tissue characteristic of the stems, leaves and roots of the higher plants.
Besides, they belong to the haploid generation whereas those of the higher plants represent
the diploid generation. The organs which are similar in function but different in origin are
said to be analogous.

The thallus-like plant body of bryophytes bears the gametes.
It is concerned with sexual reproduction and constitutes the most conspicuous,
nutritionally independent phase in the life cycle.

Reproduction:

The sexual reproduction is of oogamous type. The gametes are produced in complex sex
organs. The sex organs are multicellular, jacketed. Each sex organ consists of an outer,
protective wall of sterile cells surrounding the cell or groups of cells which produce the
gametes. The sex organs are not exposed. Hence, these plants are described as
Cryptogams (Gr. Kruptos=hidden, Gamos=wedded).

The male sex organ is called antheridium and female sex organ is called archegonium.
Both kinds of sex organs may be developed on the same individual or on distinct plants.
The former are called monoecious and the latter dioecious.

Antheridium: it is multicellular, ellipsoidal club-shaped.
It is borne on a short stalk which attaches the it to the gametophyte tissue. The body of the
antheridium has a wall of a single layer of sterile cells. It surrounds a mass of small
squarish or cubical cells called the androcytes.

The androcytes produce the biflagellate male gametes called the sperms. They are motile
structure. Each sperm usually consists of a minute, slender, spirally curved body
furnished with two long, terminal, whiplash type flagella.

Archegonium:

The female sex organ of the bryophytes is called the archegonium.
It appears for the first time in the liverworts and mosses ad continues in the pteridophytes.

The archegonium is flask-shaped organ. The slender, elongated upper portion is called the

neck and the lower-sac like swollen portion, the venter. The venter is attached to and often

deeply embedded in the parent plant tissue.

The neck has a wall of a single layer of sterile cells which surrounds a central row of

elongated, naked cells called the neck canal cells. The neck is usually projecting or freely

exposed so as to be accessible to sperms.

The venter also has a wall of sterile cells one or more cell layers in thickness.
The venter wall encloses two cells. They are the larger egg cell or the ovum and the

smaller ventral canal cell just above it.

Fertilisation:

It occurs when the sex organs are mature. Moisture is essential for the maturing of the sex

organs and also for the movement of the sperms to the archegonia.

The mature antheridium ruptures at its apex liberating the sperms. At the same time the
axial row of neck canal cells including the ventral canal cell in the mature archegonium
disorganize. The tip of the archegonium also opens. A narrow canal opening to the
exterior is formed. It acts as a passage way to the ovum in the venter.

The liberated sperms swimming in a thin film of water reach the archegonia. They enter
through the open necks and swim down the canals of the archegonia. Reaching the venter
one of them, probably the first one to reach there, penetrates the ovum. It fuses with the
nucleus of the ovum to accomplish fertilization.

With the act of fertilization the gametophyte generation ends and the sporophyte
generation starts. The gametes (sperms and eggs) are the last structures of the
gametophyte.

SPOROPHYTE

With fertilization starts the second phase in the life cycle of the bryophytes. It is called
the sporophyte. The pioneer structure of this phase is zygote.

Zygote: The fertilized egg or ovum secretes a cellulose wall around it and is called the
zygote. The latter has a diploid nucleus which contain chromosomes of both the male
and the female gametes. The zygote marks the beginning of the sporophyte generation
in the life cycle.

It is neither independent of the parent gametophyte plant nor passes into the resting
condition. In both the respects it differs from the zygote of the Green Algae. The further
development of the zygote into the embryo occurs within the venter of the archegonium
which protects the egg, the zygote and the embryo against the vagaries of external
environment such as desiccation.

Embryo: within the venter of the archegonium the zygote undergoes segmentation and
develops without a resting period into a multicellular, undifferentiated structure called an
embryo. It obtains its nourishment directly from the thallus or the parent gametophyte to
which it is attached.

The zygote of the bryophytes has thus a better chance for growth as compared with the
zygote of the thallophytes which is always independent. The latter accounts for the absence
of embryo stage in the thallophytes.

Classification

Schimper (1879) gave the rank of a division to Bryophyta as it is used at present.
Eichler (1883) divided Bryophyta into two sub-groups, Hepaticae (Liverworts) and the
Musci (Mosses). Engler (1892) sub-divided each of the two classes into three order as
follows:

Bryophyta

Class

Hepaticae or Liverworts Musci or Mosses

Order

Marchantiales Jungermaniales Anthoceratales Sphagnales Andreales Bryales

The anamolous position of Anthocerotales as an order of the class Hepaticae was pointed out
by many botanist. However, it was Howe (1899) gave the class status to the order anthocerotales.
He named it Anthocerotes and divided Bryophyta into three classes Hepaticae, Anthocerotes and
Musci.

Rothmaler (1951) suggested the following taxons for the old ones; Hepaticopsida for Hepaticae,
Anthoceropsida for Anthocerotes and Bryopsida for Musci. The new names suggested by
Rothmaler have been recognized by the International Code of Botanical Nomenclature.

Proskauer (1957) changed the name Antheceropsida to Anthocerotopsida. The modern
Bryologists classify Bryophyta into the following three classes namely, Hepaticopsida,
Anthocerotopsida and Bryopsida.