Fungal infections, especially those caused by opportunistic species, have b
ecome substantially more common in recent decades. Numerous species cause h
uman infections, and several new human pathogens are discovered yearly. Thi
s situation has created an increasing interest in fungal taxonomy and has l
ed to the development of new methods and approaches to fungal biosystematic
s which have promoted important practical advances in identification proced
ures. However; the significance of some data provided by the new approaches
is still unclear, and results drawn from such studies may even increase no
menclatural confusion. Analyses of rRNA and rDNA sequences constitute an im
portant complement of the morphological criteria needed to allow clinical f
ungi to be more easily identified and placed on a single phylogenetic tree
Most of the pathogenic fungi so far described belong to the kingdom Fungi;
two belong to the kingdom Chromista. Within the Fungi, they ape distributed
in three phyla and in 15 orders (Pneumocystidales, Saccharomycetales, Doth
ideales, Sordariales, Onygenales, Eurotiales, Hypocreales, Ophiostomatales,
Microascales, Tremellales, Poriales, Stereales, Agaricales, Schizophyllale
s, and Ustilaginales).