OPHIOGLOSSALES. I: AN OVERVIEW

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 for 15 years chiefly from the localities where more than one species of Ophioglossum 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 species O. eliminatum is being suspected to have been arisen by natural hybridization and chromosomal elimination. O. eliminatum has the lowest count n = 90 in the genus.