This was originally described as a variety of Dasyscyphus emerici. Apothecia of the type of that species (India, Nilgiri Hills, on dead stem (? Rubus), no. 90) though similar in general appearance, have a somewhat darker disc and shorter, non-septate spores 18-26 x 1.7-2.5 µm, smaller asci 75-85 x 5-0-6.5 µm and hairs which are almost always swollen and thicker walled at the apex. The taxa seems closely related but, in view of these differences and that of substrate, are probably best regarded as specifically distinct. The relationship between the present species and L. melanophthalmum is also close. Lachnum nothofagi lacks the dark disc of that species and rarely has any resinous exudate on the hairs, and although there is little difference in hairs, spore length or ascus size, it is probably specifically distinct.

Variation in spore length has frequently been noted for related species of Lachnum and, unless large numbers of collections are available, as examined for example by Haines & Dumont (1984) in their investigation of the long-spored lignicolous taxa, species delimitation may present difficulties and require subsequent revision. The two Australian collections here interpreted as conspecific with L. nothofagi differ slightly in spore length but agree well in other respects and do not provide evidence for a continuous series linking this species with L. melanophthalmum and Dasyscyphus emerici. There is intergradation and no great difference in spore length between them and, although one collection (Beaton 93) has some apothecia with hairs apically encrusted with amber-coloured resin, they probably fall within the range of variation of a single species.

Dennis (1961) discussed the relationship of L. nothofagi with the Javanese Dasyscypha javanica Penzig & Saccardo and D. ochroleucus Penzig & Saccardo. The former was shown by Haines (1980) to be a synonym of D. oncospermatis and is evidently restricted to fern stems. However, the latter, on bark in Java, is very like L. nothofagi with spores described as 27-28 x 3 µm and, as figured by Penzig & Saccardo, (1904), very similar in shape, but lacking septa. I have not seen material but it is possible that this may provide an earlier name for L. nothofagi.