Lachnum hyalopus (a Phormium specialist), Lachnum apalum var. beatonii (a Juncus specialist), and unnamed Lachnum species on Carex (PDD 117556), Astelia (PDD 71062) and Cyathea (PDD 112178) are phylogenetically very close. Collectively, their ITS sequences have a 98.7% match and the various species lack unique sets of consistent nucleotide changes. Backing up the host-related species structure are morphological differences, especially in ascospore size and shape of the excipular cells.

L. apalum var. beatonii has longer ascospores than L. hyalopus (40-65 µm versus 30-45 µm); short-cylindric, more or less square, excipular cells versus long-cylindric excipular cells; hairs undifferentiated compared to slightly swollen at the tips. The species on Astelia has ascospores 15-20 x 2.5 µm, short and broad excipular cells and hairs slightly swollen at the tips. The species on Cyathea has ascospores 55-75 x 2 µm and long-cylindric exipular cells.

Another Juncus-inhabiting species (PDD 108737) is phylogenetically distinct within Lachnum, has shorter ascospores that match a New Zealand specimen Spooner (page 661) identified as L. apalum, but compared to the specimen examined by Spooner, PDD 108737 has non-lanceolate paraphyses and coarsely roughened hairs.

Another macromorphologically similar unnamed Juncus-inhabiting species with filiform ascospores is represented by PDD 117687 and PDD 62169, but this species has smooth-walled hairs and is phylogenetically an Albotricha sp. The same species has been found on leaves of Gahnia, Cortaderia and Chionochloa.