The Making of Genera in Fungi 321 



THE MAKING OF GENERA IN FUNGI. 



J. M. Van Hook, Indiana University. 



The question of genus making and what it takes to constitute a 

 genus, has provoked much discussion from the earliest times and we 

 are now possibly no nearer its solution than before, possibly farther 

 away. 



The object of this brief paper is to present one point of view 

 and one which is very apparent even to the youngest student of sys- 

 tematic mycology. It occurs to the student that genera are often erected 

 for convenience and for the convenience of analytic keys rather than for 

 any great scientific differences in their characteristics. He often finds 

 genera widely separated in sequence in texts, when in reality they may 

 possess only a single slight difference and this difference may not be 

 constant among the various species of the genera. As an illustration 

 of the above, we may cite the case of Pleurotus and Claudopus among 

 the Agaricaceae. The chief difference between these two genera seems 

 to be that of spore color. This single difference, and we have many 

 such genera, necessitates a separate genus because of a major division 

 of the family based upon spore color. The specimen at hand whether 

 it be a Pleurotus or a Claudopus, may be traced through the key to 

 exactly the same place except as to spore color. When, however, one 

 tries to classify such a well recognized species as Pleurotus sapidus 

 Kalchbr., he will likely refer it to the genus Claudopus on account of 

 the beautiful light grayish vinaceous spores in mass. These so-called 

 pink spores will retain their color for many months in a strong light. 

 However, after a study of the very similar oyster agaric, Pleurotus 

 ostreat7is Fr., one can scarcely make a separate species out of P. sapidus, 

 much less a genus. Certainly it belongs to the pink-spored group as far 

 as spores are concerned, although no one of experience would consider 

 it a Claudopus. 



In the group of Ascomycetes, we find the genus Rosellinia widely 

 separated from Hypoxylcn by certain mycologists on account of the sepa- 

 rate perithecia of the former and the stromatic perithecia of the latter. 

 Yet even a superficial study of the family Xylariaceae will display Rosel- 

 linia forms whose perithecia coalesce and Hypoxylcn forms whose 

 perithecia are separate. Where such forms occur, we have Rosellinias 

 that are apparently Hypoxylons and Hypoxylons that are apparently 

 Rosellinias. If broader and better characters had been chosen on which 

 to base the above genera, this confusion would not occur and these 

 closely related genera would not be placed in widely separated families. 

 In view of the remarkable similarity of the species of these genera, as 

 to habitat, external appearance and spores, we see scarcely more than 

 a subgeneric difference at the most. Saccardo .seems to be one who did 

 not fall into the usual error and used a system based upon spore-color 

 which happens to place Rosellinia where it rightfully belongs. 



In this same family (Xylariaceae), we notice the closely related 

 genera, Nummularia, Hypoxylon and Daldinia. The globose forms of 



"Proc. 38th Meeting-, 1922 (1923)." 

 21—25870 



