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 ofholdfasts that have lost most oftheir physiological functions as organs of absorption than are such alterations in roots whose functions are more complex. Ifthis hypothesis is true we would expect to find greater stability in somatic counts ofroots ofterrestrial taxa and less stability in holdfasts of epiphytic taxa. OUf 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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