Recent results from Bromeliaceae chromosome research support Marchant's proposed x = 25 as the extant base number for the family. Mitotic chromosome numbers are variable and some discrepancies exist between mitotic and meiotic counts of the same species. These may be explicable in terms of the association with the epiphytic habit. It is hypothesized that chromosomal alterations are more likely to be retained within the cells of holdfasts that have lost most of their physiological functions as organs of absorption than are such alterations in roots whose functions are more complex. If this hypothesis is true we would expect to find greater stability in somatic counts of roots of terrestrial taxa and less stability in holdfasts of epiphytic taxa. Our observations are in concordance with this hypothesis. Polyploidy appears to have been important in the evolution of the family, and a polyploid trend in Tillandsia subgenus Diaphoranthema has recently been discovered.
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