Chromosome numbers of Orthocarpus and related monotypic genera (Scrophulariaceae: subtribe Castillejinae)

A chromosome number of n = 12 is reported for the three monotypic genera of subtribe Castillejinae: Clevelandia beldingii, Gentrya racemosa, and Ophiocephalus angustifolius. Chromosome numbers of Orthocarpus correspond mostly with current infrageneric classification. Subgenus Triphysaria has n = 11. Orthocarpus sections Castillejoides and Cordylanthoides, which are closely related to Castilleja (x = 12) and the three monotypic genera above, have n = 12 with aneuploid reductions to n = 10 in O. linearilobus and n = 11 in O. lacerus (a species also with n = 12). Tetraploids are found in two species, O. brevistylus (n = 24) and O. hispidus (n = 12, 24) The polyploid O. laciniatus (n = 36, 48) of Peru is postulated to be of hybrid origin between a species of Castilleja and Orthocarpus attenuatus. Subgenus Orthocarpus section Orthocarpus, which has n = 14 in all species except O. bracteosus (n = 15), stands apart both morphologically and in chromosome number from the remainder of the genus.