Nematodes were isolated from surface-sterilised stems of cheatgrass, Bromus tectorum (Poaceae), in Colorado, grown on Fusarium (Hypocreaceae) fungus culture, and identified as Paraphelenchus acontioides. Morphometrics and micrographic morphology of this species are given to supplement the original description and expand the comparative species diagnosis. A tabular morphometric compendium of the females of the 23 species of Paraphelenchus is provided as the last diagnostic compilation was in 1984. Variations in the oviduct within the genus are reviewed to evaluate the taxonomic assignment of P. deckeri, a morphologically transitional species between Aphelenchus and Paraphelenchus. Sequences were generated for both 18S and 28S ribosomal DNA, representing the first identified species within Paraphelenchus so characterised. These sequences were incorporated into phylogenetic trees with related species of Aphelenchidae and Tylenchidae. Aphelenchus avenae isolates formed a well supported monophyletic sister group to Paraphelenchus. The ecology of Paraphelenchus, cheat grass and Fusarium is also discussed.