In this first part of monographs the families Paxillaceae and Gomphidiaceae and the subfamilies Gyroporoideae and Gyrodontoideae of Boletaceae (all Agaricales) are treated. The new combination Chroogomphus rutilus ssp alabamensis (Earle ex Sing.) Sing, and Meiorganum curtisii (Berk. ap. Berk. & Curt.) Sing., García & Gomez are proposed and sect. Pseudopaxillus is proposed as a new section of Meiorganum. Furthermore Gyrodon proximus f. minor Sing. & Gomez is described. The new combination Meiorganum agathidis (Corner) Sing. & al. (Merulius agathidis Corner) is proposed. For Paxillus aurantiacus McNabb non Ellis the new name P. mcnabbii nob. is introduced.