Fungal endophytes of Oxytropis kansuensis Bunge from China, previously described as Embellisia oxytropis Q. Wang, Nagao & Kakish, and endophytes of Oxytropis sericea Nutt. and Oxytropis lambertii Pursh from the United States were compared and are reported here as conspecific members of a new genus in the Pleosporaceae, Undifilum, based on morphological and molecular analyses. Morphological comparisons revealed characters that are similar to those of the genus Embellisia including conidia ovate to obclavate to long ellipsoid, straight or slightly to decidedly inequilateral with occasionally one or two cells distinctly swollen, and transepta occasionally thickened, dark, and rigid in comparison with the exterior conidium wall. However, upon germination, conidia produced unique and diagnostic germ tubes that were wavy or undulating in their growth until branching. Moreover, all isolates were found to produce the toxic alkaloid swainsonine. Parsimony analysis of sequences from ITS1–5.8S–ITS2, glyceraldehyde-3-phosphate dehydrogenase gene, and mitochondrial small subunit rDNA data sets revealed that the Oxytropis endophytes formed a clade distinct from other Embellisia species and species in the genera Alternaria , Ulocladium , Nimbya , and Crivellia . A second taxon, Helminthosporium bornmuelleri P. Magnus, was reexamined and found to possess similar morphological features to those of the Oxytropis isolates, but lacked swainsonine production. Sequence analysis placed this second taxon in the same clade with high bootstrap support. The distinct morphology and genetics of these taxa demonstrates that these fungi, both recovered from legumes, represent a new genus, hereinafter described as Undifilum . The two species now placed in this genus are redescribed as Undifilium oxytropis and Undifilium bornmuelleri .

Endophytic Undifilum oxytropis (Q. Wang, Nagao & Kakish) Pryor, Creamer, Shoemaker, McLain-Romero, & Hambleton found within toxic locoweeds ( Astragalus and Oxytropis spp.) produces the alkaloid swainsonine, which is responsible for locoism in grazing animals. We sought to determine the location of U. oxytropis within locoweed seed, develop endophyte free plants, and assess the influence of environmental stresses on locoweed and endophyte cultures. Undifilum was identified within the parenchyma layers in seeds of Astragalus lentiginosus M.E. Jones using light microscopy and polymerase chain reaction. Astragalus lentiginosus and Oxytropis sericea Nutt. seedlings produced in embryo culture without seed coats did not contain swainsonine or fungus. Plants produced from whole seed contained U. oxytropis in both foliage and root tissues. When the in-vitro cultured plants of O. sericea and U. oxytropis cultures were subjected to environmental stresses including high temperature, low and high pH media, nutrient deficient media, and polyethylene glycol (PEG) amended media to simulate water deficit, both dry mass and swainsonine levels were affected. Swainsonine levels were greatest for O. sericea and Undifilum cultures in PEG or hydrochloric acid amended media. Plants grown in PEG-amended media had significantly greater dry mass, while Undifilum grown in PEG-amended media had lower dry mass than other treatments.