THE LICHEN FLORA OF THE SANTA CRUZ PENINSULA 255 



C. Surface not isidiose. 



D. Apothecial margin not fringed with thalline lobules. 



I . pulverulenta 

 DD. Apothecial margin fringed with thalline lobules. 



4. venusta 

 CC. Surface isidiose. 



E. Medulla white 3. pulverulenta isidiigera 



EE. Medulla greenish yellow or sulfur 5. muscigena 



A A. Thallus not pruinose. 



F. Thallus brownish gray to oHve and dark, brown. 

 G. Thin and very closely appressed, not sorediate. 



10. adglutinata 

 GG. Thallus thicker, sorediate, marginally hispid. ... 11. obscura 

 FF. Thallus white, gray, or ashy. 



H. Thickly sprinkled with small white, sub-epidermal spots. 



/. Under surface with simple white fibrils 6. stellaris 



II. Under surface with hispid black fibrils 7. aipolia. 



HH. Thallus without sub-epidermal white spots. 



/. Lobes flat; marginally sorediate 8. tribacia 



J J. Lobes ascendant, with vaulted inflated tips; not 



sorediate 9 • ienella 



I. 



PHYSCL\ PULVERULENTA (Schreb.) Nyl. 



Lichen pulverulentus Schreher, SpidL 128. 1771. 



Physcia pulverulenta Nyl. Act. Soc. Linn. Bord. ser. 3. 1: 308. 



1856. 

 Physcia pulverulenta Tuck. Syn. N. Am. Lich. I: 72. 1882. 

 Physcia pulverulenta Herre, Proc. Wash. Acad. Sci. 7: 361. 1906. 



Thallus orbicular or stellate; the numerous lobes usually long and 

 broad, laciniate, crenate, their margins sometimes dissected, tips 

 rounded; central lobes sometimes short, rounded, imbricate, with 

 retuse tips; color greenish to brownish, the upper surface more or 

 less white pruinose; beneath black, or marginally white, densely 

 black fibrillose; medullary layer white or greenish white. 



Apothecia wanting or imperfectely developed. 



On stones in the foothills. Recorded by Hue from nearly all over 

 the world. 



2. PH\^SCL\ PULVERULENTA ARGYPILEA Nyl. 



Physcia pulverulenta argyphcea Nyl. Lich. Scand. 104. 1861. 

 Physcia pulverulenta argypJuBa Herre, Proc. Wash. Acad. Sci. 7: 361. 

 1906. 



