Biology Notes on Bryophyta | Plants

This article provides a short note on bryophyta.

Introduction to Bryophyta:

It was realised in the later eighteenth century that it was not quite scientific to divide the Plant Kingdom into the two subkingdoms Cryptogamia and Phanerogamia as was done in the classical systems of classification. Four main divisions of the Plant Kingdom— Thallophyta, Bryophyta, Pteridophyta and Spermaphyta (seed plants) seemed to be more appropriate.

A. P. de Candolle (1819) divided the Plant Kingdom into the Cellulares (Thallophyta and Bryophyta) and the Vasculares (Vascular plants). Endlicher (1826-40) divided the Plant Kingdom into Thallophyta and Cormophyta.

In the 1880’s, Engler also suggested that the Plant Kingdom be divided into two groups—the Thallophyta and the Embryophyta, the latter to include all the plants excepting the thallophytes as in all these the zygote develops a multicellular embryo. The Embryophyta has been called Cormophyta by Endlicher, Eichler and other authors because of the definite solid Cormus type plant body.

Another term, Telemophyta, in place of Embryo­phyta, has been suggested by Takhtajan (1953) on the basis of the Telome Theory.

In his Syllabus der Pfanzenfamilien, Engler divided the Embryophyta into two divisions (abteilungen):

(i) Embryo­phyta asiphonogama or the Archegoniatae which includes the Bryophyta and the Pterido­phyta 

(ii) Embryophyta siphonogama or the Spermaphyta. In the latest edition of the Syllabus (1954) the Thallophytes have been divided into 13 divisions and the Embryophyta into 4 (Bryophyta, Pteridophyta, Gymnosperm, and Angiosperm).

By the early twentieth century it became clear that the vascular plants (i.e., the Pterido- phytes and the Spermaphytes) form a rather distinct group within the Embryophyta and some authorities suggested that these should form a distinct group named Trachaeophyta.

According to the International Code of Botanical Nomenclature the Plant King­dom has to be divided into a number of divisions each ending in the suffix-phyta.

There is no rule about intermediate groupings (subkingdom, etc.). Tippo (1942) divided the Plant Kingdom into the subkingdoms Thallophyta and Embryophyta as proposed by Engler and then subdivided each of them into phyla, a term not regular for Botany and should be changed to divisions according to the International Code.

The Embryo­phyta are divided by him into Bryophyta and Trachaeophyta. Takhtajan (1953) and others, however, do not think Trachaeophyta as natural and puts Bryophyta within other Trachaeophytes considering it as a reduced form from Trachaeophytes.

In the latest classification by Cronquist, Takhtajan and Zimmermann (1966) the Plant Kingdom has been divided as follows:

Subkingdom Thallobionta (=Thallophytes)

Subkingdom Embryobyonta (=Embryophytes or Cormophytes or Telemophytes)

Division Rhyniophyta (=Psilophytales)

Division Bryophyta

Division Psilotophyta (=Psilotales)

.. and other Trachaeophyte divisions.

It may thus be seen that while the terms Cryptogamia, Phanerogamia have become obsolete and the term Pteridophyta still open to dispute, Bryophyta still stands as a definite entity. But, still there are some doubts as to whether the Bryophyta should be con­sidered as a division or as a subkingdom.

Bold (1957) has suggested that Bryophyta should he considered as a subkingdom comprising of two separate divisions—Hepaticophyta and Bryophyta. In that case, the subkingdom should be called Bryophytae, along with the two other subkingdoms—the Thallophytae and the Trachaeophytae.

Characters of Bryophytes:

The Bryophytes, generally, form a natural group where the common plant body is a gametophyte, whereas in the Trachaeophytes the common plant is a sporophyte. They represent a phase in evolution when plants migrated from water to land. Water is so much necessary for the completion of their life history that we may describe them as the amphoebians among plants.

The bryophytic gametophyte is either a thallose structure or becomes foliose in the foliose hepatics and the mosses. In mosses there is also a temporary filamentous form of the gametophyte, called the protonema. The protonemal stage is also present in the Hepatics but the protonema in this group is merely a continuous first stage of gametophyte formation and not a separate stage as in the mosses.

The gametopbytic body is green with chlorophyll and possesses rhizoids and scales for absorption although it may be able to absorb through its whole surface. In the foliose forms, specially, in the mosses, the terms ‘stem’ and ‘leaf’ are often applied to the organs.

But, this is not quite correct as here the plant body is a gametophyte and not a sporophyte as in the higher plants (Trachaeophytes) where the terms ‘stem’ and ‘leaf’ correctly apply. It is perhaps more appropriate to use the terms phyllid (for leaf-like appendages of gametophytes) and caulid (for the apparent stems) as suggested by Koch (1958).

The Bryophytic gametophytes are independent autophytes. The sex organs, antheridia and archegonia, are multicellular structures within which the gametes (eggs and Mediate sperms) are developed. The embryo develops within the venter of the archegonium and ultimately develops the sporophyte.

Unlike the Tra­chaeophytes, this sporophyte is a very rudimentary structure, completely parasitic on the gametophyte and devoid of such common organs as leaf or root or even regular vascular tissues. At most it is differentiated into a haustorial foot, a seta— the forerunner of the stem, and a capsule which last is the sporangium developing spores by reduction division.