LETTER No. 46. 



FOREIGN STEREUMS IN OUR MUSEUM. 



(By C. G. Lloyd, written at Kew, April, 1913.) 



We have received in the past from foreign correspondents quite a 

 number of Stereums which we were unable to name, as we were only 

 familiar with the species of Europe and United States. We have spent 

 a couple of months at Kew, studying there the rich collection of foreign 

 species, and comparing our specimens, and have since worked over the 

 specimens at Leiden, Berlin, and Paris. 



We take the genus Stereum in the original Friesian sense, but would 

 modify it to include the species with hyaline spores. It is quite difficult 

 to decide - what distinction the old mycologists made between Stereum 

 and Thelephora. We would restrict Stereum to those species that have 

 hyaline spores, and Thelephora to those with colored, angular spores. 

 While this is a microscopic distinction and as a general rule we do not 

 favor basing genera on such differences, it is a practical division and the 

 genera can be recognized by the eye: There are very few species of 

 Thelephora in the tropics under this definition. 



The genus Stereum can be broken up in several ways, we think to 

 not much advantage. Patouillard considers the stipitate species as form- 

 ing a genus, but we can not see why a stipe in Stereum is of more im- 

 portance than a stipe in Polyporus, which he does not divide on this 

 character. There are various types of "hairs," (or cystidia as they are 

 called), and Leveille, Cooke, and others would form genera on these hairs. 

 In practice it will be found to be very much of a "hair-splitting propo- 

 sition," for there are half a dozen different types of hairs and they grade 

 into each other so it is impossible to draw a line between the different genera 

 if they are based on these "hairs." Besides, the same hairs have as much 

 value theoretically in all other groups, for Agarics, Hydnums, Polypores, 

 and even Tremellaceae have these hairs, and no one ever attempts to 

 make genera on them excepting in the Thelephoraceae. 



While "hairs" on the hymenium may be a convenient character to sub- 

 divide the excessively numerous, resupinate species, which otherwise afford 

 few characters to group into sections or "genera," like everything else 

 that is good in moderation, it has been carried to excess by recent writers. 

 Particularly by von Hohnel, who bases a "new genus" (and adds "von 

 Hohnel" to each species) on every shape, size, exudation, coloration, and 

 position of hairs that he finds on the hymenium. 



The genus Stereum is not so large that it is necessary to resort to 

 any such strategy, and it is much simpler and better in my opinion to take 

 Stereum in its generally accepted use and meaning. The genera Peniophora 

 and Hymenochaete in the sense of Cooke (in part) and the recent genus 

 Lloydella have little value for me. 



UNIVERSITY OF CALIFORNIA 



AT LOS ANGELES 



