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The locoweeds Astragalus and Oxytropis in the Americas and China, as well as Swainsona in Australia, harbor swainsonine-producing endophytes responsible for “locoism” or “pea struck” syndromes in grazing animals. Demonstration of Alternaria section Undifilum spp. requires demonstration of morphological characters such as a wavy germ tube and slow growth. While Astragalus wetherilli, A. pubentissimus, Swainsona canescens, and S. galegifolia plants have been shown to contain swainsonine, and fungi isolated from the plants have been partially characterized genetically, the fungi have not been characterized morphologically. This work sought to complete morphological characterization and determine species for those fungi and from fungi associated with Swainsona luteola and S. brachycarpa. The fungi were isolated from their hosts onto media and exhibited slow growth, resulting in a colony diameter of approximately 10 mm after 30 days. Morphological identification revealed production of conidia that produced a wavy germ tube for the endophytes from Astragalus pubentissimus species, Swainsona canescens, and S. galegifolia. Sequence analyses of the ITS region and the swnK-KS and swnK-TR genes of these fungi suggest that the fungi isolated from Astragalus are closely related and distinct from the fungi isolated from Swainsona. Presence of the swnK gene demonstrates that all the fungi have a necessary component to produce swainsonine. Fungi isolated from Astragalus spp. differed in color, growth, and conidium size, and/or their sequences. While the fungi isolated from Swainsona canescens and S. galegifolia endophytes differed in color, growth, and conidium size, those isolated from Swainsona luteola and S. brachycarpa did not produce conidia. Sequences from all Swainsona endophytes were almost identical and were concluded to be the same species. The new species described here are Alternaria wetherii, A. pubentissima, A. pubentissimoides, and A. swainsonii.