Prof. J.A. Nannfeldt gave in a lecture (publ. in Acta Univ. Skrifter rörande Uppsala Univ. 17, 1970) an interesting summary of Fungi as plant taxonomists, distinguishing 4 cases: 1) isolated fungus restricted to one species, not on other related species, 2) an isolated single fungus on a supraspecific taxon of hosts, 3) closely related fungi on closely related species of hosts, 4) parasite genera or higher taxa confined to a special super-generic host taxon. All cases he illustrated by examples. In certain cases there must have been ’co-evolution’ of parasite and host. He mentioned that the importance of parasitic fungi as indicators of taxonomic affinity has been utilized in the past. Samuelsson used it in 1913 for example to suggest affinity of Empetrum with Ericaceae. One could say that this means of getting independent data is an argument of chemotaxonomical nature, the ’taste’ of the parasite for certain substances which he needs, likes or is bound to in some other way. Prof. Nannfeldt, besides pointing to Empetrum, added that we must now seriously consider the possibility, or rather probability, of a kinship between Acorus and Sparganiaceae after the surprising discovery of Parmelee & Savile who found that Uromyces sparganii also infests Acorus calamus (1954).