RBCL SEQUENCES PROVIDE PHYLOGENETIC INSIGHTS AMONG SISTER SPECIES OF THE FERN GENUS POLYPODIUM

Opinions on the phylogeny and classification of the Polypodiaceae sens u stricto have been particularly divergent and recent DNA sequencing a nalyses have supported the hypothesis that this group should be allied to the higher indusiate ferns. Within the genus Polypodium, isozymic and restriction site analyses demonstrated that interspecific genetic identities are quite low, suggesting that sequences of the conservativ e rbcL gene would be appropriate for addressing open systematic questi ons. Average infrageneric sequence divergence (1.87%) was sufficient t o generate reliable species differences, and the skewness test of rand omly generated trees suggested that the data were non random and proba bly phylogenetically informative. A strict consensus of the eight most parsimonious trees supported the monophyly of the P. vulgare complex, and decay analysis showed that primary tree branches were well suppor ted. Most of the phylogenetically informative nucleotides were at thir d codon positions. Neotropical Polypodinm species were chosen a priori as a close out-group, and emerged as a sister group to the P. vulgare complex. Polypodium amorphum + P. appalachianum formed a clade that w as morphologically supported by the synapomorphic feature of sporangia sters in the sori. Although the indication that P. glycyrrhiza was rel ated to the Asian species P. fauriei was not unexpected, the close ass ociation of these two species with P. scouleri was quite surprising, a nd provided insights on the possible origin of the latter species thro ugh adaptation to stressful habitats. Whereas the long held hypothesis of a close association between P. australe and P. macaronesicum was u pheld, the rbcL sequence data could provide no insights on the phyloge ny of the enigmatic Hawaiian endemic, P. pellucidum. Pleopeltis thyssa nolepis, until recently classified as a Polypodium, was solidly allied to Pleopeltis macrocarpa var. complanata. It is anticipated that futu re molecular analyses will provide additional insights on the evolutio nary history of the Polypodiaceae.