real lactifers and do not extend into the hymenium as pseudocystidia. This traditional distinction line between the "milk-caps" and Russula is however less evident in some tropical species presenting intermediate states. Genera distinction Some characteristics of the mushroom-forming genera (marked with * below) can be less obvious or absent in tropical species. Distinguishing between Lactarius and Lactifluus based on morphology alone is quite difficult, as clear synapomorphies for both genera have yet to be identified. Most field guides treat the two genera together, often because Lactifluus is not yet recognised as a separate genus. Boidinia: corticioid; loose texture; surface smooth, with pores, or flaky; spores spherical with spiny to warty ornamentation. Note that the genus is polyphyletic and needs to be redefined. Gloeopeniophorella: corticioid; surface almost smooth; hyphae without clamp connections; thick-walled cystidia (metuloids) and gloeocystidia present; spores with wrinkled (rugose) ornamentation. Lactarius: agaricoid or gasteroid; exuding latex*; caps sometimes zonate, viscose or glutinate, but never annulate; rarely thick-walled cells in cuticles of the cap (pileipellis) and the stipe (stipitipellis) and sphaerocytes in the gills. Lactifluus: agaricoid or pleurotoid; exuding latex*; caps never zonate, viscose or glutinate, but sometimes annulate; thick-walled cells in cap and stipe cuticles; often sphaerocytes in the gill trama. Multifurca: agaricoid; caps zonate (also visible in cut through trama); gills regularly forked; only M. furcata exuding latex; spore print orange; spores very small; microscopical trama and hymenium features very variable. Pseudoxenasma: corticioid; wax-like texture; gloeocystidia with spherical apical appendices; basidia developing laterally on hyphae (pleurobasidia); spores broadly ellipsoid to roughly spherical, with warty ornamentation. Russula: agaricoid, gasteroid or pleurotoid; never exuding latex; caps often brightly coloured with stipe and gills much paler; caps not zonate*; spore print white, cream, ochre, or orange; no true lactiferous hyphae*; sphaerocytes abundant in gill, cap, and stipe trama. Distribution The Russulaceae as a whole have a worldwide distribution, but patterns differ among genera. Russula is the most widespread, found in North, Central and South America, Europe, temperate and tropical Asia, Africa, and Australasia. It is the only Russulaceae genus that occurs in the Nothofagus zone of temperate South America. Lactarius is mainly known from the north temperate zone, but some species also occur in tropical Asia and Africa. Lactifluus has a more tropical distribution than Lactarius, with most species known from tropical Africa, Asia, South America, and Australasia, but some also occurring in the north temperate zone. Multifurca is the