Ch. Haufler et Ta. Ranker, RBCL SEQUENCES PROVIDE PHYLOGENETIC INSIGHTS AMONG SISTER SPECIES OF THE FERN GENUS POLYPODIUM, American fern journal, 85(4), 1995, pp. 361-374
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.