Heteroploid twins and apomixis in Casuarina nana Sieb.

Abstract

Casuarina nana Sieb. occurs in some localities as a diploid, with a somatic chromosome number of 22, and in others as a tetraploid (2n = 44), and there is evidence of hybridization between these two chromosome forms. In one population of this species diploid, triploid, and tetraploid plants occur together. Heteroploid twins, with 33 and 44 chromosomes respectively, are regularly produced in seeds from the triploids. A reproductive system involving apomixis is suggested, and supported by embryological evidence.

A similar situation apparently exists at other localities. These populations may have resulted from hybridization between the diploid and tetraploid forms, and illustrate a stage in the development of obligatory apomixis.