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The number of chromosomes possessed by a species, which may be given as either the haploid (n) or diploid (2n) number. Chromosome number is important taxonomically since it is usually constant within a species. There are however many exceptions especially in species exhibiting reproductive abnormalities, e.g. apomixis. Among flowering plants the average haploid chromosome number is about 16 though this varies from n = 2 in the composite Haplopappus gracilis to extremely high numbers in certain polyploid series. For example, in the allopolyploid Spartina townsendii (saltmarsh grass) n = 60. It is thought that the original haploid chromosome number in angiosperms was in the region 7-9 and that numbers higher than n = 14 are polyploid in origin.
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