Cytotaxonomy of ®Ophioglossales III.

Chromosome Numbers and Systematics of Ophioglossum

Abstract

1) Two species and a variety of Japanese Ophioglossum were examined cytotaxonomically and the systematic position of Ophioglossales was discussed.
2) O. vulgatum showed 240 distinct gametic chromosomes without exception.
3) Four cytological races were found in O. petiolatum. Materials from four populations, Narita c, Usui, Nikko and Choshi, have n =480, and those from Inage, n=510-520. Very irregular meiosis was observed in materials from three populations, Toke, Togane and Kyoto. Those from Toke and Kyoto probably have 2n =ca. 960, while Togane material may have 2n=ca. 1100.
4) Two cytological races were found in O. thermale var. nipponicum. Apparently 480 bivalent chromosomes were counted in the material from Narita d population. The materials from Narita e and Kyoto show irregularity in meiosis, but their somatic chromosome number was estimated to be about 960.
5) No correlation between chromosome number and form of plant was found in comparing each cytological race, even in the very polymorphic species, O. petiolatum.
6) Ninan's suggestion that the primary basic chromosome number of Ophioglossales may be 15 was verified.
7) Section Vulgata is considered a more modified derivative than Aitchisonii in view of chromosomal constitution, since the latter shows no such chromosome numbers as high as 240, 480, 630, etc.
8) In respect of spores O. vulgatum and O. petiolatum can be discriminated easily, no matter how they resemble each other in cytological and morphological features.
9) Ophioglossales is considered a very specialized group far apart from other modern ferns, phylogenetically.
The authors wish to express their cordial thanks to Mr. T. Namegata, President of Nippon Fernist Club, for providing many materials for the present study.