The 2009 edition of MeSH contains 25,186 descriptors and more than 180,447 supplementary records for chemicals and other substances. For the 2009 edition, the MeSH Section added 446 new descriptors, replaced 123 descriptors with more up-to-date terminology and deleted 26 descriptors. Of special note are developments for 2009 MeSH related to fungi and to processes and phenomena. A major revision of the “Fungi” trees was undertaken to reflect consensus opinion regarding higher level fungi taxa (Mycology Research 111 (2007) 509- 547). Additionally, two tree categories were changed to separate disciplines from processes and phenomena studied by.
