The UM Herbarium contains an outstanding collection of the hydnums of North America. Its foundation was laid by C. H. Kauffman while making his studies of the Agaricaceae of Michigan and since has been greatly enlarged through the collections made by A. H. Smith. In the last two years I have had the opportunity to study these collections. This is the first of two papers based on them and gives keys and descriptions for the identification of all genera and species found to date in the state with details on a few species that can be expected when collecting is expanded into counties not explored as yet. Hydnums are exacting in their growth requirements and many kinds fruit only in restricted areas, or during favorable seasons after long intervals of time. It takes years to build up the necessary collections for even a modest flora of any region and this makes the yearly records from Michigan uniquely valuable. It is hoped that this paper will stimulate interest in these rare fungi so that additional favorable collecting areas can be located and a more complte understanding of the requirements of the species obtained. It is of interest to point out that the distributions given in these papers are the most complete for any comparable area in North America but the more common species have been recorded from only 10 of the 83 counties in the state. In the paragraphs on material examined, the collections cited are from Michigan unless otherwise stated.