THE LICHEN FLORA OF THE SANTA CRUZ PENINSULA 65 



XII. Arthonia. 



Arthonia Ach. Lich. Univ. 25. 1810. 

 Arthonia A. Zahlbr., Ascolichenes, 89. 1907. 



The alga is Trentepohlia. Apothecia innate, surrounded by the 

 thallus, circular, dot-like, or irregularly stellate, or more or less elon- 

 gate; spores variously shaped, oval, ellipsoid, wedge-like, or needle 

 shaped; bi- or multilocular, the cells often of unequal size; colorless 

 or rarely brown. 



About 500 species, mostly of the warmer parts of the earth, on 

 bark and rocks. 



KEY TO SPECIES. 



Thallus pinkish or reddish when wet; spores 4 locular punctiformis 

 Thallus not changing color when wet; spores 4 -locular radiata 



i. ARTHONIA PUNCTIFORMIS Ach. 



Arthonia punctiformis Ach. Lich. Univ. 141. 1810. 



Arthonia punctiformis Willey, Synopsis Genus Arthonia, 41. 1890. 



Thallus white or whitish, forming more or less determinate spots 

 or blotches, thin, uniform, sometimes evanescent; when moistened 

 becoming pinkish or reddish; no reaction with chemicals. 



Apothecia small or minute, slightly elevated, rounded, oblong or 

 irregular, black; epithecium granulose, blackish; thecium pale, the 

 asci pear-shaped; reaction with I first bluish, than wine-red; accord- 

 ing to Hasse "indigo-blue"; spores oblong-ovoid, 4~to 6-locular, 



4-6 

 12 - 19^ ^ 



Found fertile on Vaccinium on White Horse Creek, and on Alnus 

 on the Gazos Creek, near the sea coast; I also refer here a sterile 

 lichen which is abundant on the stems of Baccharis pillularis and 

 other shrubs. A lichen of Europe and North America. 



2. ARTHONIA RADIATA (Pers.) Th. Fr. 



Opegrapha radiata Persoon, Ust. Ann. 29. 1794. 



Arthonia radiata Th. Fr. Lich. Arctoi, 240. 1860. 



Arthonia radiata Willey, Synopsis Genus Arthonia, 44. 1890. 



Thallus thin, uniform or slightly scaly, determinate, often limited 

 by a black hypothalline line; color, various shades of gray to olive 

 and fawn-color; no reactions with KOH or CaCl 2 O 2 . 



