ranges from 17 mm diameter or less in Russula campinensis to in Lactifluus vellereus. Concentrically ringed (zonate) caps occur in all Multifurca and several Lactarius species. Laterally striped (pleurotoid) fruitbodies exist in some, mainly tropical Lactifluus and Russula species. Taste is a distinguishing characteristic in many species, from mild to very acrid. A conspicuous feature of the "milk-caps" in Lactarius, Lactifluus, and Multifurca furcata is the latex or "milk" their fruitbodies exude when bruised. The secotioid and gasteroid species in Lactarius and Russula are derived from agaricoid forms. Secotioid species still have a stipe but the cap does not open fully, while in gasteroid species, fruitbodies are completely closed and the stipe is reduced; in both cases, the spore-bearing structure is made up of convoluted gills that are more or less crowded and anastomosed. These closed-fruitbody species represent a continuum of secotioid to gasteroid, above-ground to below-ground fruitbodies, with spores forcibly discharged or not. Secotioid or gasteroid Lactarius exude latex just like their agaricoid relatives. The corticioid species of Boidinia, Gloeopeniophorella, and Pseudoxenasma develop crust-like fruitbodies with a smooth, porous, or flaky surface and grow on tree logs or dead branches. Microscopic characteristics All Russulaceae, including the corticioid species, are characterised by spherical to elliptic basidiospores with a faint to very distinct (e.g. warty, spiny, or crested) ornamentation that stains bluish-black with Melzer's reagent (an amyloid stain reaction). Basidia (spore-bearing cells) are usually club-shaped and four-spored. Russulaceae species do not have clamp connections. Characteristic cells with an oily content (gloeocystidia) are found in the hymenium. In Russulaceae, these show a positive colour reaction when treated with sulfoaldehydes (sulfovanillin is mostly used). They are also present in the hyphal sheath of ectomycorrhizal roots colonised by Russulaceae. The feature responsible for the brittle fruitbody structure in the mushroom-forming species are globular cells, called sphaerocytes or sphaerocysts, that compose the flesh (trama) alongside the usual hyphae. Sometimes, these cells are clustered, and the position and arrangement of these clusters differs among genera. Another particular trama cell type are lactiferous hyphae (also lactifers). These are hyphae carrying the "milk" or "latex" exuded by the milk-caps; they react positively with sulfoaldehydes, form an abundantly branched system in the trama and end as pseudocystidia in the hymenium. In general, only Lactarius, Lactifluus and Multifurca furcata possess lactifers. In Russula, similar hyphae can sometimes be observed in the trama, but these are not as abundantly branched as