Phylogenetic ordinal placement based on rDNA sequences of the freshwater genera Ophioceras and Pseudohalonectria.

The ordinal placement of two closely related freshwater genera, Ophioceras and Pseudohalonectria, was assessed by using phylogenetic analysis of morphological characters, partial sequences of the large subunit ribosomal DNA and restriction site variations in the internal transcribed spacer (ITS). The two genera have some morphological features that are used to define taxa in both the Sordariales and Diaporthales, and, hence, their phylogenetic relationships are unclear. Equally weighted analyses of thirty-eight morphological characters produced unresolved phylogenetic trees and unequivocal conclusions could not be drawn based on the morphological data. The polymerase chain reaction-amplified ITS region was variable in length between the two genera and restriction sites in the ITS region were determined. Analysis of variation in restriction sites in the ITS region placed Ophioceras and Pseudohalonectria in one clade with taxa sampled from Sordariales. About 350 basepairs of DNA sequence from the 5' end of the large subunit rDNA were also determined. In phylogenetic analysis of the sequence data with Hypocrea lutea and Nectria cinnabarina as outgroups, Ophioceras and Pseudohalonectria showed a closer relationship to Neurospora crassa, Schizothecium sp., and Sordaria fimicola of the Sordariales than to Cryphonectria parasitica and Endothia gyrosa of the Diaporthales.