Castilleja dissitiflora N. Holmgren is a montane species, endemic to central Nevada, and a tetraploid (2n=48). It is thought to be a genomic allopolyploid descendant of a cross or crosses between C. linariifolia Benth. (2n=24) and C. applegatei Fernald ssp. pinetorum (Fernald) Chuang & Heckard (2n=24). This hypothesized relationship is based on the fact thatC. dissitiflora is intermediate between the two putative parents in floral morphology and overall aspect. Although currently, C. dissitiflora is only sympatric with one putative parent, C. linariifolia, the other putative parent, C. applegatei ssp. pinetorum approaches it to within 200 km on the west and north of its range. It is commonly held that allopolyploids are most successful when the parents are not close relatives, for if they are, tetrasomic inheritance may generate unbalanced gametes. Although the two putative parents are both in subgenus Castilleja, C. linariiflora is is in section Castilleja, whereas C. applegatei is in section Viscidulae. The phylogenetic relationship among sections of Castilleja can reveal just how close or distant these two sections are. Sequences of the plastid trnK intron and nuclear ITS are used along with morphology and new chromosome counts to assess the validity of the hypothesized allopolyploidy. A skeletal phylogeny of the genus Castilleja is used to determine the degree of relationship between the sections with the two putative parent species. Castilleja is a member of the newly redefined Orobanchaceae.

Key words: allopolyploid speciation, Castilleja dissitiflora, chromosome counts, ITS, Orobanchaceae, trnK intron