The Bromeliaceae is characterized by a 2n chromosome number of 50, but exceptions have been reported. These include scattered polyploids and presumed aneuploid reductions in isolated species from subfamilies Tillandsioideae and Bromelioideae, and 2n = 34 or 36 for all species of Cryptanthus (Bromelioideae) thus far examined. Two hypotheses have been proposed that address the origin of the low chromosome number (2n = 34 or 36, compared to 50) in Cryptanthus. We have attempted to test these hypotheses using quantification of nuclear DNA by flow cytometry. DNA quantifications for examined Cryptanthus species fell into two groups. In one there was no significant difference between Cryptanthus and selected bromeliad species known to have 2n = 50. In the second, Cryptanthus species had approximately twice as much 2C nuclear DNA. Results partially support the hypothesis that the Cryptanthus chromosome number (2n = 34) originated by descending aneuploidy, a derived condition which, with other apomorphies, supports the hypothesis that Cryptanthus is derived within the subfamily Bromelioideae. First chromosome number reports are presented for two species of Cryptanthus and one species of Orthophytum.

Communicating Editor: Alan Whittemore