Chromosome Numbers and Polyploidy in Castilleja (Scrophulariaceae)

Chromosome numbers are reported for 155 collections of Castilleja representing 54 taxa. The basic haploid number of 12 was found in 34 taxa, but 10 of these also had one or more polyploid levels. The remaining 20 species were strictly polyploid in one or more levels (4X, 6X, 8X, 10X, 12X). The widespread occurrence of polyploidy, along with hybridization, is believed to be largely responsible for the complex morphological variation found within the genus. Specific examples of the role of polyploidy and hybridization in creating this variation are discussed for the following species complexes: C. affinis, C. applegatei, C. miniata, C. peckiana.