THE LICHEN FLORA OF THE SANTA CRUZ PENINSULA 165 



A cosmopolitan genus of about 200 species, occurring on rock, 

 bark, and moss; frequently sterile or with the apothecia degenerate, 

 forming heaps of soredia, when the species are often difficult or 

 impossible to determine satisfactorily. 



KEY TO THE SPECIES. 



A . On rocks ......................................... i. pertusus 



A A. On bark. 



B. Thallus conspicuously sorediate and more or less marginally 

 sorediate; sterile. 



C. Thallus bitter to the taste, like quinine ............ 2. amara 



CC. Thallus not bitter ......................... 3. globulifera 



BB. Soredia absent or inconspicuous. 



D. Thallus usually sulfur-yellow ...................... 4. wulfenii 



DD. Thallus white or cream-colored. 



E. Thallus milk-white; apothecial warts brownish red 



with CaCl 2 O 2 .................................. 5. velata 



EE. Thallus cream-colored to grayish white. 

 F. Apothecial warts lecanorine; disk pruinose, pale flesh- 

 color when moistened and rubbed ............. 6. lecanina 



FF. Apothecial warts not lecanorine. 



G. Thallus not affected by KOH; spores 2 or i. 



7. pustulata 

 GG. Thallus yellow with KOH; spores 3, 4, 5, or 6; 



rarely 2 ................................. 8. leioplaca 



i. PERTUSARIA PERTUSUS (L.) 



Lichen pertusus Linne, Mantissa, 2:134. 1771. 



Pertusaria communis DeCandolle, Flora France, 2 : 230. 1805. 



Pertusaria communis Tuck. Syn. N. Am. Lich. I: 214. 1882. 



Thallus thick (rarely thin), chinky, areolate and rough warty; 

 determinate, more or less orbiculate, or often spreading extensively, 

 the margin more or less zonate; color clear gray to dusky gray; KOH 

 yellowish, becoming orange-red; CaCl2O2 . 



Apothecial warts numerous, of medium size, adnate, flattened, 

 sub-globose or difform, usually crowded; the apothecia ordinarily 

 five or six in each wart, but varying from one to 12 in number; 

 ostioles black or very dark, minute, from elevated becoming de- 

 pressed; epithecium violet with KOH; spores usually in twos, also 



solitary, in threes, or fours; 



140 - 188 



