Karyomorphology of Biebersteinia Stephan (Geraniaceae) and its systematic and taxonomic significance

The systematic and taxonomic position of Biebersteinia Stephan has long bee n in dispute. The present paper describes for the first time the karyomorph ology of two species in Biebersteinia Stephan. Both species commonly showed the interphase nuclei of the simple chromocenter type and the mitotic prop hase chromosomes of the interstitial type. The karyotype formulae of both B . heterostemon and B. odora were 2n=10=2m(2sec)+8sm(2sec), belonging to the 3A type of Stebbins' classification. The karyotype of this genus is record ed for the first time. The basic chromosome numbers of four of the five kno wn species of Biebersteinia have been recorded as x=5. The combination of r esting nuclei of the simple chromocenter type, mitotic prophase chromosomes of the interstitial type, two pairs of chromosomes with four obvious secon dary constrictions at the mitotic prophase and metaphase stages, and the pe culiar 3A karyotype in Biebersteinia can be regarded as the karymorphologic al marker of this genus. The karyomorphological data presented here do not support the traditional grouping of this genus in Geraniaceae. The unique k aryomorphology of Biebersteinia justifies its familiar or ordinal status, w hich is congruent with embryological, anatomical, chemical and molecular da ta. The systematic position of Biebersteinia needs further study.