88 14. ARTHONIACEAE [47. Arthonia 



to subglobose, black; hymenium hyaline; hypothecium pale brown; asci pyriform; 

 spores hyaline, oblong-ovoid, 1-septate, one cell larger, 10-14X4.5-5.5/1.. 

 On trees and old wood, New Bedford, Massachusetts. 



44. Arthonia pruinosella Nyl., in Hasse. Lich. South. Calif. 16. 1898. 



Thallus thin to rather thick, uneven and sometimes becoming scurfy, forming 

 small, round to irregular, dirty white or cream-colored patches; apothecia minute, 

 0.1-0.15 mm. across, round to rarely somewhat irregular, immersed to adnate, the 

 disk flat, black or more commonly grayish pruinose; hypothecium hyaline; spores 

 hyaline, oblong-ellipsoid, 1-septate, 13-16 X 4-5 ft. 



On trees, southern California. 



45. Arthonia aleuromela Nyl, Bot. Gaz. 22:334. 1896. 



Superficial thallus dull white, thin to moderately thick, smooth, becoming pow- 

 dery; apothecia minute to small, 0.2-0.6 mm. across, partly immersed to adnate, 

 round to somewhat irregular, the disk flat to irregular or strongly convex, black; 

 tinged brownish within; spores ovoid-ellipsoid, 1-septate, 10-13 X 1.5-3.5 /x. 



On trees, West Virginia. 



46. Arthonia Rhoidis Zahlbr., Beih. Bot. Centralb. 13:156. 1902. 

 Superficial thallus thin, pale pinkish to grayish, smooth to slightly rough; 



apothecia minute to small, 0.1-0.25 mm. across, immersed, round to irregular and 

 sometimes oblong, the disk flat, black; hyaline within; asci pyriform; spores hya- 

 line, ovoid-ellipsoid, 2-septate, 12-14 X 4.5-6 xx. 

 On trees, southern California. 



47. Arthonia dispersa (Schrad.) Nyl., Not. Sallsk. Faun. Flor. Fenn. 5:261. 



1861. 

 Opegrapha dispersa Schrad., Usteri, Ann. der Bot. 22:86. 1797. A. astroidea 



var. epipasta (Schrad.) Nyl. 

 Superficial thallus thin, ashy white, smooth to slightly rough; apothecia minute 

 to small, 0.09-0.4 mm. across, partly immersed, round to irregular, or sometimes 

 elongated, rarely branched, the disk flat to convex, dark brown to black, rarely 

 grayish pruinose; hyaline or tinged pale brownish within; asci pyriform; spores 

 hyaline, oblong-ovoid, 1-septate, 11-16 X 4-5 /x. 



On trees, generally distributed throughout the United States. 



48. Arthonia Willeyi Tuck.; Hedrick, Mycologia 25:311. 1933. 



Superficial thallus dull white, of moderate thickness, smooth to slightly rough; 

 apothecia minute to small, 0.1-0.35 mm. across, round to slightly irregular, partly 

 immersed to adnate, the disk flat to convex, black; tinged pale yellowish within; 

 asci pyriform; spores hyaline, ovoid-ellipsoid, 1-septate or rarely 2-septate, one 

 cell larger, 10-13 X 3-4 ft. 



On trees, near Athens, Illinois. 



4'). Arthonia Cytisi Mass., Nouv. Ann. Sci. Nat. Bologna 7:21b. 1853 



A. excipienda Nyl. A. hibemica Nyl. 



Superficial thallus ashy white, thin, smooth, sometimes disappearing; apothecia 

 minute to small, 0.1-0.4 mm. across, immersed or partly immersed, irregular and 

 often more or less branched, the disk flat, black; tinged pale brownish within; 

 spores ovoid-ellipsoid, hyaline, 3-septate, one end cell larger, 16-25 X 5.5-9 /x. 



On trees, Massachusetts, Ohio, and California. 



50. Arthonia dispersula Nyl., Flora 59:285. 1876. 



A. Austini Willey. 



Superficial thallus thin, ashy white, smooth to slightly rough; apothecia minute 

 to small, 0.1-0.4 mm. across, partly immersed to adnate, round to irregular, the 

 disk flat to convex, black; tinged brownish within; spores hyaline, ovoid-ellipsoid, 

 1-septate, one cell larger, 8-11 X 3-4.5 /x. 



On trees, Florida. Scarcely distinct from A. dispersa, spores slightly smaller. 



