Eleven species and five subspecies of the genus
Ixeris s. lat. were karyologically investigated. Somatic chromosome numbers and karyotypes of
Ixeris polycephala (2n=16),
I. chinensis ssp.
strigosa (2n=24),
I. transnokoensis (2n=14), and
I. makinoana (2n=14) were examined for the first time. Further, the karyotypes of
I. repens,
I. chinensis complex, and
I. laevigata, were also described. As a result, plants with x=8 and small relative chromosome length, and those with x=7 and large relative length, were recognized in the genus. The former group possesses the rod or round prochromosome type of resting nuclei, but the latter has the diffuse chromosome type. These karyological features proved to be good criteria for defining
Ixeris and other related genera, since they match very well with gross morphological as well as anatomical characters. The species of
Ixeris examined thus were divided into two groups on the basis of chromosome morphology. The first group, with x=8 and similar karyotypes, is composed of
I. repens,
I. stolonifera,
I. debilis,
I. longirostrata,
I. polycephala,
I. chinensis complex and
I. tamagawaensis. The second group, with x=7, comprises the
I. dentata complex,
I. laevigata,
I. transnokoensis, and
I. makinoana. In conclusion, the species with x=7, which have been referred to sect.
Ixeridium, no doubt represent a distinct phylogenetic group, and should be separated from those with x=8 as an independent genus.
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