Ophioglossales are the natural group of early vascular plants
which exhibit the most simple and most complicated combinations of characters
comparable to bryophytes, pteridophytes, progymnosperms, gymnosperms and
angiosperms. Essentially, pteridophytes these plants are often referred and
classified as ferns. However, there are some fundamental differences which
should not justify their present alliance. The chief "genetic loss"
in plants of this group can be presumed to be the loss of capability of
producing sclerenchyma. Also, the sporangia are unlike ferns; they do not have
an annulus and are supplied with vascular tissue. Additionally, absence of
circinate vernation and presence of periderm (in about 22% of Ophioglossum
population) make them "unlike ferns".
The conventionally recognised three genera, Botrychium,
Helminthostachys and Ophioglossum constitute a single family Ophioglossaceae of
the order Ophioglossales. Nevertheless, intergeneric differences are so pronounced
that recognition of three separate families viz. Botrychiaceae,
Helminthostachyaceae and Ophioglossaceae by some taxonomists are quite
justified. Botrychium and Ophioglossum are further divided to have subgenera;
Botrychium has Sceptridium, Eubotrychium and Osmundopteris, while Ophioglossum
has two, viz. Ophioglossum and Ophioderma. Population cytogenetic studies have
been carried out chiefly from the localities where more than one species of
Ophiglossum grow. Repeated meiotic studies have also been carried out from
populations of single or isolated species of Ophioglossum and monotypic
Helminthostachys. Numerous teratologies of genetic importance have been
described. Role of natural selection is being assessed. Lately, a new specis O.
eliminatum is being suspected to have been arisen by natural hybridization and
chromosomal elimination. O. eliminatum has the lowest count no = 90 in the
genus.
Molecular genetic data generated in many laboratories have
proved that the genus Ophioglossum in particular, is highly suitable for
studies in evolutionary genetics and we can decipher highly complicated
evolutionary mechanisms of the entire group of plants. The cotwin control
approach on vegetatively reproducing plants connected with stolons until maturity
have opened up a new technique of experimental controls for certain sets of
experiments. In fact now we need to take use of all possible morphological,
biochemical and molecular genetic techniques to understand evolutionary
mechanisms.
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