Bryophytes have a very long geological history and are known from Carboniferous to the present. They have played a very important role in forming ground vegetation since the remote past.
The spore morphology of Bryophytes has not received adequate attention though it has been proved that bryophytic spore morphology is very useful in taxonomy. Roth, at the beginning of the 20th century described spore morphology of mosses paying attention to their colour, size and sculpturing of the wall. Knox (1939) emphasized the exine ornamentation of spores of liverworts. Actually, moss spore morphology has been studied in greater detail than in liverworts. The spore wall was distinguished into three major layers from inside to outside, intine, exine and perine.
Among the liverworts spore morphology of different species of Anthoceros has been worked out extensively. Different species of Anthoceros can be identified on the basis of the characters of a triradiate mark and wall sculpturing pattern.
In the species of Cyathodium four evolutionary lines have been recognized based on spore morphology.
1. Cyathodium acrostichum, C. africanum, C. tubrosum have spiny exine in the spores.
2. Spores of C. smaragdimum have granulose exine.
3. Varrucose exine is seen in the spores of C. foetidissimum.
4. Spores with reticulate exine occur in C. spruceanum.
The noteworthy feature of bryophytic spores is the absence of aperture in the spore wall for the liberation of germ cells. It can be concluded that bryophytic spores have a limited value in the taxonomy and do not have any practical applications.
B: SPORE MORPHOLOGY OF PTERIDOPHYTES
Pteridophytes have been classified in many different ways by different pteridologists. However, according to the presently acceptable view, pteridophytes are classified into four major groups such as Pteropsida, Psilopsida, Lycopsida and Sphenopsida.
All these groups have well preserved fossil ancestors and representative genera and species. Isospores, miospores, microspores, megaspores and sporangial structures producing them have been well preserved in the form of fossils. Some of them find applications in palynostratigraphic correlation, which is widely used in the exploration of fossil fuels such as coal and oil.
Of all the groups of pteridophyta, spore morphology of ferns has been well worked out. Hence in this chapter spore morphological characters of ferns will be briefly described. The main objective of this account is to facilitate identification of fossil fern spores. Although the fern spore is in many ways similar to the pollen grains of seed plants, it occupies a position equivalent to the seeds of higher plants, being the chief instrument of dispersal. In fact, the spore is often loosely termed as the 'fern seed', and recognized as such in fern propagation.
The spores of pteridophyta, like the pollen grains of seed plants, have a highly resistant outer protective coat. Consequently they are well preserved in most of the fossil-bearing horizons, ranging from the Palaeozoic to the present, making them favourable objects for microfossil analyses. A detailed study of spores of living pteridophytes is essential for properly indentifying fossil pteridosphytic spores.
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