ORDER LECANORALES (tHE DISK LICHENS) 



223 



Mi 



Fig. 74. Lecanorales, Family Physciaceae. Physcia sp. (A) Spermogonium. (B) Anther- 

 idial filament with sperm cells. (After Kny: Botanische Wandtafeln.) 



Zahlbruckner (1926) believed that the group treated here as a single 

 order, the Lecanorales, is really polyphyletic, i.e., derived from nonHchen 

 forming fungi at many different points. Nannfeldt (1932) discussed this 

 problem and showed that some of the perithecial lichens (Order Py- 

 renulales) are in reality more closely related to the Order Pseudosphae- 

 riales and that of the lichens with true apothecia many have their closest 

 relationship not with other lichens but with Pezizales that are not lichen 

 producing. Perhaps the ultimate logical disposition of the disk hchens 

 will be to distribute them among the other apothecium-forming fungi 

 at the points where their apothecial structure and manner of sexual repro- 

 duction seem to fit best. Until the enormous mass of study needed to 

 acquire this information has been carried out it may be best to treat them 

 as a single order. 



The forms here included in the Lecanorales are divided by Zahlbruck- 

 ner into about 37 families, about 275 genera, and over 7400 species. They 

 occur from the tropics to the Antarctic and Arctic zones and from sea 

 level to the tops of the highest mountains where rock is exposed. They 

 furnish the chief food of the caribou, the reindeer, and the musk ox. Some 

 species are used for human food in famine times. Iceland moss, Cetraria 

 islandica (L.) Ach., is sometimes used for medicine. Litmus and orcein 

 are derived from Hchens. Miss Annie L. Smith's (1921, 1926) publications 

 on these fungi should be studied for a more complete understanding of 

 this extremely variable group of organisms. 



