Chromosome numbers and karyotype evolution in holoparasitic Orobanche (Orobanchaceae) and related genera
Chromosome numbers and karyotypes of species of Orobanche , Cistanche , and Diphelypaea (Orobanchaceae) were investigated, and 108 chromosome counts of 53 taxa, 19 counted for the first time, are presented with a thorough compilation of previously published data. Additionally, karyotypes of representatives of these genera, including Orobanche sects. Orobanche and Trionychon , are reported. Cistanche ( x = 20) has large meta- to submetacentric chromosomes, while those of Diphelypaea ( x = 19) are medium-sized submeta- to acrocentrics. Within three analyzed sections of Orobanche , sects. Myzorrhiza ( x = 24) and Trionychon ( x = 12) possess medium-sized submeta- to acrocentrics, while sect. Orobanche ( x = 19) has small, mostly meta- to submetacentric, chromosomes. Polyploidy is unevenly distributed in Orobanche and restricted to a few lineages, e.g., O . sect. Myzorrhiza or Orobanche gracilis and its relatives (sect. Orobanche ). The distribution of basic chromosome numbers supports the groups found by molecular phylogenetic analyses: Cistanche has x = 20, the Orobanche -group ( Orobanche sect. Orobanche , Diphelypaea ) has x = 19, and the Phelipanche -group ( Orobanche sects. Gymnocaulis , Myzorrhiza , Trionychon ) has x = 12, 24. A model of chromosome number evolution in Orobanche and related genera is presented: from two ancestral base numbers, x h = 5 and x h = 6, independent polyploidizations led to x = 20 ( Cistanche ) and (after dysploidization) x = 19 ( Orobanche -group) and to x = 12 and x = 24 ( Phelipanche -group), respectively.