Only such literature has been and will also further be treated and included, where rather comprehensive descriptions have been published. Articles considering but a few characters, are only regarded when the data given could be used to complement an already existing more detailed data set, in order to confirm features or to increase the range of variability already known. When ectomycorrhizae from different hosts are described, the data of each "host genus × fungal species" combination is regarded as independent and therefore included separately. The reason for doing this is that possibly in forthcoming fungal taxonomy it may become apparent that some fungal species which are presently regarded as homogeneous, are likely to consist of several separate taxa. For example Paxillus involutus, commonly accepted as a well defined species, can be divided into separate entities with respect to host preference and crossing behaviour (Fries 1985: Mycotaxon 24: 403-409. - Hahn & Agerer 1999: Nova Hedwigia 69: 241-310). A second example is Pisolithus tinctorius which suggested the existence of three biological groups due to intersterility groups and spore morpholgy (Kope & Fortin 1990: Mycologia 82: 350-357). Different host specificity (Malajczuk et al. 1990: New Phytol. 114: 627-632) also suggests the existence of some independent taxa within this species. New species of Pisolithus have recently been described (Bougher & Syme 1998: Fungi of Southern Australia). Very likely these two examples are not the only ones which in the future will possibly reveal to be composed of different taxa, perhaps even of separate species. As it is almost impossible or at least very time-consuming to separate a combined computer data set, the optimal strategy is to separate the ectomycorrhizal data of a fungus given on the basis of the host genus involved. The cited literature expected to being included is sometimes not exhaustive. It will be included in later versions of DEEMY.
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