Abstract
Mentha spicata L. (including M. viridis L. and M. Iongifolia (L.) HUDS.) can be divided into 4 groups in accordance with the number of chromosomes. That is, there are strains with 24, 36, 48 and 54 chromosomes in the somatic cells. In the present study, we took up the strains with 24 and 48 chromosomes as the subject of genome analysis. The strains with 24 chromosomes are given the genome formula RR like M. rotundifolia (L.) HUDS. In the strains with 48 chromosomes, there are two kinds of genome constitution. One is presumed to have RRSS, the other is RRScSc, where S and Sc are partially homologous genomes. Genome constitution in M. spicata L. is found to have no connection with the hairiness of the mint plant, which BRIQUET used as a criterion for the classiflcation of species in the series ‘Silvestres’ ; nor does it have any connection with the crispness, of the leaves, though he established a special subspecies crispata BRIQ. in M. viridis L. and a special subspecies undulata BRIQ. in M. longifolia (L.) HUDS., based on this character. In two triploid hybrids RRS and RRSc, some trivalent chromosomes can be seen in meiosis, so it is presumable that S and Sc are not entirely independent of R, but certain relations seem toexist between them. We also think that R grenome evolved into Sc and Sc into S. On the basis of this presumption, we tried to construct a family tree of the Spicatae section which included M. spicata and M. rotundifolia, as was shown in the Fig. 6.
