General characters, reproduction and classification of Bryophytes

May 31, 2018

Introduction

Derived from two Greek words (Bryon: Moss; phyton: plant).
Includes liverworts, hornworts and mosses.
Commonly known as amphibians of plant kingdom because they grow on amphibious habitat (moist habitat).
Worldwide in distribution on most parts of the earth wherever there is sufficient moisture to sustain plant life.

General characteristics

Mostly grow in moist and shady places. Some species are aquatic e.g. Riella, Ricciocarpus natans and Riccia fluitans. Some grow in xerophytic conditions like Polytrichum.
Temperature and moisture play an important role in the distribution of bryophytes.
Haploid gametophytic and diploid sporophytic generations are two distinct generations shown by plants.
The reproductive organs in gametophyte are independent and long lived, while the spores in sporophytic phase is dependent on the gametophyte and is short lived.
The gametophytic plant body may be thallose (not differentiated into stem and leaf) or foliose (differentiated into rhizoids, stem and leaves).
The vascular tissues are absent. The plant body consists of simple parenchymatous cells.
The thalli of primitive forms remain attached in the substratum by unicellular smooth walled or tuberculate rhizoids (Riccia, Marchantia).
However, in higher forms the rhizoids are branched and multicellular.
In some bryophytes multicellular scales are present, which provide protection to the growing point e.g. Riccia, Marchantia.

Reproduction

It is brought about by vegetative and sexual means.
Vegetative propagation is the most common method of propagation in bryophytes, which occurs by various ways:

Sexual reproduction is Oogamous types.
It takes place by the formation of male reproductive organ, antheridia and female reproductive organ, archegonia. Reproductive organs develop directly on thallus (Riccia, Pellia) or on special branches such as Marchantia, Porella.
Antheridium is a globose or elongated club shaped structure, develops on a stalk which consists of androcytes, surrounded by jacket layer.
Each androcyte metamorphoses into a single, uninucleate, biflagellate antherozoid.
Archegonium is a flask shaped structure consisting of a basal swollen portion, the venter and an elongated slender, the neck.
Water is essential at the time of fertilization.
The zygote divides and re-divides to form sporophyte. There is no resting period.
The sporophyte of Riccia is very simple; consists of capsule only, whereas in other bryophytes it consists of foot, seta and capsule.
The capsule contains sporogenous tissues which divide meiotically to form four haploid spores.
Spore is the first cell of gametophytic generation, which on germination gives rise to gametophytic plant body.
The life cycle of bryophyte shows regular alternation of gametophyte and sporophytic generation.

Classification of bryophytes

i) Hepaticopsida (or Hepaticae)

ii) Anthoceortopsida (or Anthocerotae)

iii) Bryopsida (or Musci)

1) Hepaticopsida (liverworts) or hepaticae

Hepatica is a Latin word which means liver so members of this class are commonly called
This name was applied to certain plants during the middle ages due to their liver-shaped bodies.
The plant body is gametophyte and thallose or foliose.
The plant body is prostrate and dorso-ventrally differentiated in thallose.
The leaves are always without a midrib in foliose.
Scales and rhizoids are present in ventral surface. The unicellular rhizoids are smooth walled as well as tuberculate.
The sex organs develop on the dorsal surface usually, whereas in some case in terminal position.
Sporophytes are simple, consist of a capsule only, whereas in some cases they are differentiated into foot, seta and capsule.
Sporogenous cells develop from endothecium zone of capsule.
Sporophyte depends upon gametophyte.
The capsule contains elaters for the dispersal of spores.
e.g. Riccia, Marchantia, Porella, etc.

2) Anthocerotopsida or Anthocerotae

The gametophyte is very simple, small, prostrate, dorsoventrally differentiated thallus.
No internal differentiation of tissues in thallus.
Rhizoids are only smooth walled and the ventral scales are entirely absent.
Antheridia develop on the dorsal side of the thallus from hypodermal cell.
Archegonia are almost completely embedded in the tissue of the thallus on the dorsal side.
The sporophyte consists of a bulbous foot, an intercalary meristematic region and along cylindrical capsule.
Sporogeneous tissues are derived from amphithecia.
e.g. Anthoceros, Megaceros, Notothylas, etc.

Anthoceros Notothylas

3) Bryopsida or Musci

It is the largest class of the Bryophyta.
The gametophyte is differentiated into gametophore and protonema.
The gametophore consists of axis (stem) and spirally arranged leaves.
The rhizoids are present on both protonema and gametophore. They are multicellular and branched.
The sex organs develop on apical portion of the stem.
The sporophyte consists of a foot, a seta and a capsule.
The sporogenous cells develop from the outer layer of endothecium and usually enclose a columella.
The sporogenous tissue gives rise to spores only. Hence the sterile cells (elaters) are absent.
e.g. Funaria, Polytrichum, Sphagnum, etc.

Funaria Polytrichum

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I am Shailesh Koirala