| Abstract: | Najas graminea is first reported to have a population of 2n = 12. A cytogeographicsurvey of this species reveals that the diploid (2n= 12) population is so far only found inYunnan (You Jun 8804, in Herb. WH) and its adaptive radiation has probably resulted in thedistribution pattern of N. graminea today in Asia. The polyploids are more widely distributedthan the diploid, but no correlation was found between polyploids and geographic distribution, soil or climate types. The comparison of the karyotypes between diploid and hexaploid,lack of inter-specific hybridization in nature, and the occurrence of semi-cryptic polyploidsin the populations suggest that polyploids of N. graminea are the result of autopolyploidy (atleast in China). The highest polyploidy (almost 17X), the most asymmetrical karyotype, andthe most reduced floral structure (the spathe is absent) support the suggestion that theN. graminea be the most advanced taxon in Najas. |
