Abstract
Studies into the cytological behaviour in the genus Ophioglossum have been undertaken especially from a cytogeographical and cytotaxonomical bias. The present investigation reveals the haploid chromosome number in an Australian population of Ophioglossuon coriaceum A. Cunn. to be 510 and it includes 10-14 very small bivalents. This number is incidently a mul-tiple of 15 and lends further support to Ninan's (1956a) suggestion that 15 is probably the common base number of the family Ophioglossaceae. -However, keeping in view the discrepancies in chromosome numbers in some Ophioglossum species, in particular O. polyphyllum (cf. Table 1) and Helminthostachys (n=94, Ninan Lc) it seems desirable to make further enquiries in this direction especially as Stebbins (1950) has also pointed out that the higher the number the more are the ways in which it can be compounded. Apart from repeated allopolyploidy the present writer, on the basis of the existence of multivalents in a form of O. vulgatum (Verma 1956), emphasizes also the role of autopolyploidy. Furthermore, vegetative reproduction is responsible for supporting diverse chromosomal constitution and the initial sterility arising out of autopolyploidy.
Taxonomic status of Ophioglossum coriaeemn is discussed in the light of Claussen's (1938) morphological observations and the available cytological data on the related species O. lusitanicum (Manton 1950b and Ninan 1956a) as well as other widely distributed species like O. vulgatum (Verma 1956). It is suggested that O. coriaceum should not be treated as a distinct species but rather be merged within the polymorphic O. lusitanicum. Pending fur-ther studies on more parts of its range, it is at present regarded as a distinct cytogeographical race and thus be treated as a ssp. of O. lusitanicum, as pro-posed earlier by Claussen on the basis of morphology and geographical distribution.
Based on observations on O. vulgatum and O. lusitanicum (sensu Claussen, 1938), it is suggested that the genus Ophioglossum as a whole be regarded as a group of facultative apomicts. Furthermore, the species concept in the genus should be on more or less similar lines as adopted for apomictic angiosperms (cf. Stebbins 1950).
Present cytological data reveals that the species with wider distribution show numerous cytological races as well as high number. Furthermore, there is probably a gradual increase in the chromosome number from Northern to Southern latitudes. This formulation, however, needs further study on widely distributed species.
