Studies on the Cytology and Phylogeny of the Pteridophytes

Abstract

1. A critical cytological investigation of nine species of Ophioglossum (including several cytological and geographic races), one species of Botrychium and the monotypic Helminthostachys has been made.2. The lowest haploid number for Ophioglossum is n=120 and for Helminthostachys, n=94.3. Almost all the species of Ophioglossum investigated in the present study (excepting the aneuploid series in O. reticulatum and perhaps O. vulgatum) are found to form a polyploid series based on the haploid number n=120.4. O. reticulatum L. is shown to have the highest chromosome number yet recorded in any species (n=c. 630, 2n=c. 1260).5. The basic chromosome number of the Ophioglossaceae is postulated to be 15.6. Evidences of chromosome numbers obtained from this study show the probability that there is some parallelism in the cytological evolution of the Ophioglossaceae and the Schizaeaceae. Both Ophioglossum and Schizaea exhibit very high chromosome numbers. The basic number 15, characteristic of the Ophioglossaceae, is also shared by Lygodium, the most primitive genus of the Schizaeaceae.7. Cytological evidence is in favour of regarding Botrychium as the most primitive of the three genera while Helminthostachys is intermediate and Ophioglossum the most specialised.8. There is no cytological support for the segregation of species of Botrychium and Ophioglossum into subgenera or for raising these subgenera to generic status.9. It is suggested that the greater percentage of polyploids as well as higher grades of polyploidy encountered in South Indian races of Ophioglossum may be related to the fact that Peninsular India is geologically one of the oldest land masses with a continued vegetation cover for a very long geological period. This suggestion is incidentally supported by evidences of chromosome numbers from ancient genera like Tmesipteris and Phylloglossum from Australia which also represents a very old geological formation.10. The taxonomic delimitation in species like O. reticulatum, O. petiolatum and O. vulgatum is seen to be very artificially drawn.11. Taxonomic revision in the light of cytology is necessary for O. nudicaule.