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Media type:
E-Article
Title:
Phylogeny of Marsileaceous Ferns and Relationships of the FossilHydropteris pinnataReconsidered
Contributor:
Pryer, Kathleen M.
imprint:
The University of Chicago Press, 1999
Published in:International Journal of Plant Sciences
Language:
English
DOI:
10.1086/314177
ISSN:
1058-5893;
1537-5315
Origination:
Footnote:
Description:
<p>Recent phylogenetic studies have provided compelling evidence that confirms the once disputed hypothesis of monophyly for heterosporous leptosporangiate ferns (Marsileaceae and Salviniaceae). Hypotheses for relationships among the three genera of Marsileaceae (<italic>Marsilea</italic>,<italic>Regnellidium</italic>, and<italic>Pilularia</italic>), however, have continued to be in conflict. The phylogeny of Marsileaceae is investigated here using information from morphology and<italic>rbcL</italic>sequence data. In addition, relationships among all heterosporous ferns, including the whole‐plant fossil<italic>Hydropteris pinnata</italic>are reconsidered. Data sets of 71 morphological and 1239<italic>rbcL</italic>characters for 23 leptosporangiate ferns, including eight heterosporous ingroup taxa and 15 homosporous outgroup taxa, were subjected to maximum parsimony analysis. Morphological analyses were carried out both with and without the fossil<italic>Hydropteris</italic>, and it was excluded from all analyses with<italic>rbcL</italic>data. An annotated list of the 71 morphological characters is provided in the<xref ref-type="app" rid="ap1">appendix</xref>. For comparative purposes, the Rothwell and Stockey (<xref ref-type="bibr" rid="rf122">1994</xref>) data set was also reanalyzed here. The best estimate of phylogenetic relationships for Marsileaceae in all analyses is that<italic>Pilularia</italic>and<italic>Regnellidium</italic>are sister taxa and<italic>Marsilea</italic>is sister to that clade. Morphological synapomorphies for various nodes are discussed. Analyses that included<italic>Hydropteris</italic>resulted in two most‐parsimonious trees that differ only in the placement of the fossil. One topology is identical to the relationship found by Rothwell and Stockey (<xref ref-type="bibr" rid="rf122">1994</xref>), placing the fossil sister to the<italic>Azolla</italic>plus<italic>Salvinia</italic>clade. The alternative topology places<italic>Hydropteris</italic>as the most basal member of the heterosporous fern clade. Equivocal interpretations for character evolution in heterosporous ferns are discussed in the context of these two most‐parsimonious trees. Because of the observed degree of character ambiguity, the phylogenetic placement of<italic>Hydropteris</italic>is best viewed as unresolved, and recognition of the suborder Hydropteridineae, as circumscribed by Rothwell and Stockey (<xref ref-type="bibr" rid="rf122">1994</xref>), is regarded as premature. The two competing hypotheses of relationships for heterosporous ferns are also compared with the known temporal distribution of relevant taxa. Stratigraphic fit of the phylogenetic estimates is measured by using the Stratigraphic Consistency Index and by comparison with minimum divergence times.</p>