78 HERRE 



About 500 described species, principally inhabitants of cold or 

 temperate regions. The typical representatives of the genus are 

 especially abundant on igneous or metamorphic rocks in alpine or 

 cold regions, and are among the most difficult of plants to satisfac- 

 torily determine. 



KEY TO THE SPECIES. 



I. Section Psora : Thallus squamulose, more or less lobed. 



A. Squamules brick-red or reddish-flesh color; KOH + . . i. decipiens 

 A A. Notred;KOH . 



B. Thallus light brown to chestnut; of small to medium-sized squa- 

 mules 2. globffera 



BB. Squamules minute; dull brown-black 3. scotopholis 



II. Section Biatora: Thallus uniform, granulose or much reduced; 



apothecial margin clear or colored, but never black. 

 a. Scales large, more or less lobate ; apothecia large . 4. granulosa phyllizans 

 aa. Areoles quite small; apothecia small or minute 5. coarctata 



III. Section Eulecidea : Thallus uniform ; apothecial margin black. 



A. Thallus absent -17. auriculata diducens 



A A. Thallus usually well developed. 

 B. Thallus brown or blackening. 



C. Thallus forming small isolated patches among other lichens 



7. intumescens 



CC. Thallus indeterminate, spreading. 

 D. Hypothecium colorless or slightly brownish; no reaction 



with 1 8. manni 



DD. Hypothecium dark; 1 + 



E. Thallus brown to dark brown or nearly black; squamules 



flat to concave 6. fumosa 



EE. Thallus fawn-colored; squamules convex to sub-globose 



9. atro-lutescens 



BB. Thallus yellow, gray, whitish, or white. 

 F. White or nearly so. 



G. On bark; KOH yellow; CaCl 2 O 2 18. melancheima 



GG. On rocks. 



H. Thallus thin or very thin, marked by tortuous black lines 



ii. cruciaria 

 HE. Thallus of crumbs or scales, without tortuous black 



lines 16. goniophila 



FF. Thallus gray, grayish, or yellowish. 

 /. On bark or dead wood. 



/. Thallus gray, ashen, or whitish; CaCl 2 O 2 - ... 20. parasema 

 JJ. Thallus olive or yellow to gray and whitish; CaCl 2 O t 



brick-red 19. olivacea 



H. On rock. 

 K. Hypothecium black or black-brown. 



Thallus ashy or dusky gray 10. grisella 



KK. Hypothecium pale to brown. 



