The genus Pteridium has been nearly uniformly reported as having n=52 or 2n=104 from numerous reports covering several of the described taxa within P. aquilinum (for a summary, see Löve et al., 1977). This ploidy generally is regarded as the current diploid in the genus. However, a few exceptions exist. Löve and Kjellqvist (1972) reported a count of n=26 from a plant that they referred to P. herediae. This count, which was published without documenting photos or illustrations, was later refuted as based on an aberrant cell by Sheffield et al. (1986, 1989a). Additionally, an apparent tetraploid count of 2n=208 was reported by Jarrett et al. (1983) from the Galapagos and a second tetraploid from Malaysia and Australia was inferred by Thomson (2000a, b) based on morphometric and DNA fingerprinting data (but no cytological data). However, these unusual New and Old World polyploids are best treated as allopolyploid species separate from P. aquilinum sensu stricto (Thomson, 2004). Sheffield et al. (1993) also reported an unusual, partially fertile, triploid clone from England with 2n=156, whose taxonomic affinities await further research.
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