Abstract
Karyotypes of the seven Pyrrhocactus species were studied for the first time with Feulgen staining and CMA/DAPI banding. All showed 2n = 22 (x = 11). The karyotypes were symmetrical with 9m + 2sm pairs, excepting P. catamarcensis with 8m + 2sm + 1st pairs. They had a terminal microsatellite on short arms of pair #1. Pyrrhocactus bulbocalyx possessed a second satellited pair (#2) exclusively detected with Feulgen. Increasing asymmetry was associated with a decline in karyotype size. Fluorochrome banding, applied for the first time in Cactaceae, revealed that nucleolar chromosome pair #1 had one CMA+/DAPI− terminal band in all species related to the nucleolar organizing region; additional pericentromeric bands were found. A pattern of homogeneous sized chromosomes with median and submedian centromeres is conserved in the genus. However, karyotypes can be distinguished by a combination of cytogenetic features. Species diversification in Pyrrhocactus has not been associated with large chromosome rearrangements or polyploidy, but with cumulative small and cryptic structural changes.
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