Abstract:
The New Zealand Plantago (Plantaginaceae) comprise of about 12 taxa that include both species and sub-species. The genus has been the subject of recent molecular systematic efforts in what has traditionally been recognized as a taxonomically difficult genus. Both polyploidy and hybridism are believed have played an important role in the complex evolutionary history of the New Zealand endemic Plantago species. The present study has measured the genome sizes of most of the endemic taxa and it appears that genome downsizing has accompanied polyploidisation. The degree of genome downsizing varies significantly between different taxa and the possible reasons for this are discussed. The importance of evolutionary context in the interpretation of genome size data is also highlighted and discussed. A series of genomic in situ hybridisation (GISH) experiments have revealed that all of the polyploid species are of hybrid origin. GISH also identified two of a possible four progenitors in the octoploid taxa and suggests that the six octoploid taxa may share the same genomic composition. Fluorescence in situ hybridisation (FISH) experiments using 5S and 45S rDNA probes have further detected species-specific rDNA patterns for each taxon in the endemic Plantago, indicating that there have been extensive genomic rearrangements following polyploidisation. There is also evidence for 5S and 45S rDNA loci deletion as well as copy number reduction in the polyploids. In addition, genome-specific deletions of rDNA loci have been observed in the octoploids using sequential GISH and FISH experiments. The evolution of the endemic Plantago is discussed in light of the recent results in the contexts of genome evolution and the evolution of the New Zealand flora. Outstanding taxonomical problems within the genus are also addressed and future studies to complement the current state of knowledge of the genus are suggested.