Subdivision Holobasidiomycetidae. Basidiome pilothecial with either pileus or peridium and an underlying hymenophore. Boletoid, agaricoid or gasteroid. Context homoiomerous, lacking sphaerocytes, with or without clamp-connexions. Hymenophore various, truly lamellate, secondarily lamellate, gyrose, boletinoid, tubulate, labyrinthoid or loculate. Basidiospores either ballistosporic or statismosporic in structure, hyaline or pigmented, globose to cylindric, smooth or with a eusporial ornamentation, often with a hyaline, inamyloid myxosporium. Development gymnocarpic, hemiangiocarpic or angiocarpic. World-wide, epigeal or hypogeal, often forming ectotrophic mycorrhizal associations.

Smith & Singer (1959) proposed a 'Gastroboletus Series' associating ballistosporic boletoid genera with statismosporic secotioid and hypogeal genera. Pegler & Young (1981 ) recognized six families within the Boletales, each representing a different line of descent but developing along parallel lines, and all associated with hypogeal, gasteroid genera. In the present paper, two families restricted to hypogeal gasteroid genera, from Victoria State, Australia, are considered, namely Rhizopogonaceae Gaum. & Dodge (possibly allied to Boletaceae Chev.), and Chamonixiaceae Jülich (possibly allied to Gyrodontaceae (Singer) Heinem.).