Origin and Taxonomy of Castilleja montigena (Scrophulariaceae)

Abstract

Based on data from chromosome numbers, comparative morphology, geographic distribution, and floral nectar amino acids, a narrow endemic of the eastern San Bernardino Mountains of Southern California that has been recognized under the name Castilleja ewanii (or C. martinii ssp./var. ewanii) is interpreted as an allopolyploid (n = 24, 36) derived from diploid races (n = 12) of C. chromosa and C. martinii var. martinii. Morphological evidence indicates that introgression from C. martinzi var. martinzi into C. chromosa has occurred either on the diploid level or via backcrossing to the allopolyploid derivatives in the same mountains. Thus both dip- loid introgressants and allopolyploids derived from the same parents are postulated. The type specimen of C. ewanii falls within the diploid introgressants and that name is placed in synonymy under C. chromosa. A new name, C. montigena, is proposed for the polyploids. Castilleja montigena, which possesses recombinant morphological features of the two diploid parental species, had an additive nectar amino acid com- plement of the other two species when they were sampled in several regions at some distance from the San Bernardino mountains. Thus glutamic acid is lacking in C. chromosa and valine is lacking in C. martinii var. martinii while both amino acids are present in the polyploids. In the San Bernardino Mountains, however, diploids of both parental species also possess the additive amino acid complement, thus corrob- orating morphological evidence for limited gene exchange between the diploids in this area.