DIFFERENTIATION IN AGARIC BASIDIOMATA AND PHYLOGENETIC PROBLEMS

Since the late nineteenth century, phylogenetic considerations about higher basidiomycetes have been based mainly on a series of rather variable structures which are supposed, by the theorists concerned, to have developed in particular directions. However, unanimity in interpretation of such series is rare because it is difficult to establish whether structures are primitive or reduced and because most taxa combine both primitive and derived characters. Cladistic methods, still rarely used in mycology, may be helpful in some cases by comparing many characters; but the difficulty of determining what is primitive remains. Ontogenetic studies are a useful tool to elucidate the origin of the more complicated characters. Electronmicroscopical analyses of spore wall structures have been disappointing because similar structures appear in very different taxa. Biochemical and genetical approaches offer more promise to unravel the causes of differentiation and controlled morphogenetic expression of the genome. The behaviour of generative hyphae in the basidiome is discussed, and attention is given to the importance of a better understanding of cell growth in the different taxa.