Abstract: Investigated in this paper was the karyomorphology of the monotypic genus Circaeaster Maxim. The interphase nuclei and the prophase chromosomes were categorized to be simple chromocenter type and interstitial type respectively;the metaphase chromosomes were rather small, ranging from 3.00μm to 1.20μm in length. The karyotype was formulated as 2n= 30= 22m + 8sm. Its distinctive higher haploid chromosome number, together with its several highly reduced and specialized character states in morphology, suggests that Circaeaster is a relictual paleopolyploid group. The similar karyomorphological characteristics of interphase nuclei and prophase chromosomes between Circaeaster and Kingdonia, as well asthe similar size and morphology of their metaphase chromosomes, support the viewpoint that they are closely related and are probably best treated as a ditypic family.

Key words: Circaeaster Maxim., Karyomorphology, Systematic position