This first part of an in-depth treatment of Austrian rust fungi (Pucciniales, formerly Uredinales) contains all genera except Puccinia s.l. and Uromyces. The rust species included here belong to the families Coleosporiaceae, Melampsoraceae, Milesinaceae, Pucciniastraceae (all four in suborder Melampsorineae), as well as Gymnosporangiaceae, Ochropsoraceae, Phragmidiaceae, Tranzscheliaceae, and some taxa of uncertain position.

The introductory part consists of four chapters. Instead of a glossary, a short 'Introduction to the rust fungi' and their terminology is presented. It is based on the life cycle of a well-known textbook fungus, the host alternating Puccinia graminis. In the chapter 'Spore states and life cycles of rust fungi' persisting difficulties of rust terminology are pointed out, followed by detailed overviews of rust sori and spores (especially of aecia and uredinia) and of the diverse life cycles of rust fungi. Two tables summarise the basic modifications of the life cycle and the terms for rust sori and spore types. A brief chapter on rust nomenclature deals mainly with the consequences of the changes in Article 59 of the 'International Code of Nomenclature for Algae, Fungi, and Plants' of 2012 (Melbourne Code) for the scientific names of rust fungi. At the end of the introductory part, the arrangement of rust taxa in the book and abbreviations are explained. A list of the short determination keys completes the introductory chapters.

The main part ('Rust taxa: rust-host combinations, diagnoses, illustrations, remarks and keys') is divided into two sections: 'Melampsoraceae and related families' includes the four families of suborder Melampsorineae, followed by 'Other families and Genera incertae sedis'. According to the corresponding introductory chapter, J.C. Arthur's terms for rust sori and spores are adopted in the sense of D.B.O. Savile. The circumscriptions of families and genera in this volume largely agree with those accepted by Aime et al. (2018a) and Aime and McTaggart (2020). Full descriptions or diagnoses of families and genera are not given consistently, but in some cases morphological, taxonomic and nomenclatural issues are discussed in detail. The nomenclature of species mainly follows MycoBank (2024) and/or Index Fungorum (2024), and the checklist in Thiel et al. (2023). The species concept is still more or less in line with the views expressed in E. Gäumann's 'Die Rostpilze Mitteleuropas' (1959) which has also been the taxonomic basis of the second edition of the checklist of Austrian rust fungi by Poelt and Zwetko (1997). This checklist is also the mycofloristic basis of the present volume because a fully updated account of the rust flora of Austria (including recent publications) has been postponed and scheduled for the pending second volume. The main part lists European rust taxa (except Puccinia s.l. and Uromyces) recorded on host plants occurring in Austria until 1997, and the preliminary, partial 'Alphabetical host-parasite index' (Appendix 1) lists the European rust hosts occurring in Austria; some of this information is based on inoculation experiments cited in classic rust florae (especially those by Gäumann and Klebahn, see below).

Melampsoraceae and related families (suborder Melampsorineae). In accordance with recent molecular genetic evidence, the Coleosporiaceae are treated in a wider sense, including Chrysomyxa, Coleosporium, Cronartium, Rossmanomyces (recently separated from Chrysomyxa), and Thekopsora (recently transferred from Pucciniastraceae). The Melampsoraceae s.str. contain only the difficult genus Melampsora. The species concept adopted for this genus mainly follows two classic works, H. Klebahn's rust volume in 'Kryptogamenflora der Mark Brandenburg' of 1914 and E. Gäumann's 'Die Rostpilze Mitteleuropas' of 1959; infraspecific 'formae speciales' are discussed in several cases. The Milesinaceae include the fern rust genera Milesina and Uredinopsis, but also Naohidemyces vaccinii (recently transferred from Pucciniastraceae) with Vaccinium spp. as uredinial hosts. The generic concept within the Pucciniastraceae is far from settled, and the genera Calyptospora and Melampsorella are still accepted although they might be included with Pucciniastrum in the future; Hyalopsora and Melampsoridium are well-delimited genera.

Other families and Genera incertae sedis. This section includes a heterogeneous assemblage of the families Phragmidiaceae (Gymnoconia, Kuehneola, Phragmidium, Trachyspora, Triphragmium, Xenodochus), Gymnosporangiaceae (Gymnosporangium), Ochropsoraceae (Ochropsora), Tranzscheliaceae (Leucotelium, Tranzschelia), and two more genera which are not assigned to a family here (Nyssopsora, Triphragmiopsis).