174. Physcia ] 44. PHYSCIACEAE 387 



becoming wavy; hypothecium hyaline to brownish; spores short-ellipsoid, 26-32 

 X 15-18 ft. 



On trees, Santa Cruz Peninsula, California. 



12. Physcia obsessa (Mont.) Nyl., Mem. Soc. Imp. Sci. Nat. Cherb. 3:175. 1855. 

 Parmelia obsessa Mont., in Sagra, Hist. Nat. Cub. 227. 1842. P.integrata var. 



obsessa (Mont.) Vainio. 



Thallus small, adnate, smooth, light greenish gray to whitish, the narrow lobes 

 usually separated, moderately branched with entire to irregularly crenate mar- 

 gins; brown to black below or rarely light-colored, with dark-colored rhizoids; 

 apothecia small, 1-3 mm. across, sessile, the disk flat, white-pruinose to brownish 

 black, the exciple entire; spores oblong-ellipsoid, 15-20 X 7.5-10 /x, or larger in 

 some foreign material. 



On trees, near Sanford, Florida. 



13. Physcia callosa Nyl, Flora 52:119. 1869. 



Thallus thin to moderately thick, closely adnate, rough and wrinkled, ashy to 

 white, the lobes short, and narrow, with crenate margins, frequently passing into 

 a continuous, coarsely wrinkled, warty crust; brownish below with short, black- 

 ening rhizoids ; apothecia small, 1-3 mm. across, sessile, the disk concave to flat, 

 black, usually grayish pruinose, the exciple moderately thick, colored like the 

 thallus, irregular and wavy; spores oblong-ellipsoid, 12-20 X 5-7.5 /x. 



On arenaceous rocks, near San Francisco, California (closely related to P. stel- 

 laris) . 



14. Physcia isidiigera (Zahlbr.) Fink n. comb. 



P . pulverulenta var. isidiigera Zahlbr.; Herre, Wash. Acad. Sci. 7:362. 1906. 



Thallus small, adnate, brownish black or often bluish pruinose, coralloid or 

 powdery-granular, passing centrally into a crust, the lobes short, not much 

 branched, often imbricated, the margins ascending and crenate; black below, pale 

 toward the margins, with short black rhizoids; apothecia small, 1-2.5 mm. across, 

 the disk concave, black or sometimes pruinose, the exciple thick, elevated, soredi- 

 ate; spores oblong-ellipsoid, 32-38 X 14-20 tt. 



On trees and wood, California. 



15. Physcia muscigena (Ach.) Cromb., Brit. Lich. 1:309. 1894. 



Parmelia muscigena Ach., Lich. Univ. 472. 1810. P . pulverulenta var. muscigena 

 (Ach.) Nyl. 



Thallus middle-sized, chestnut-brown or lighter colored, white-pruinose in part 

 or throughout, the lobes short, narrow, ascending, more or less branched and often 

 bearing coralloid branchlets, the margins yellow-powdery or sorediate; white be- 

 low, or becoming dark, covered densely with black rhizoids; apothecia rare, small 

 to middle-sized, 2-4 mm. across, sessile, the disk concave to flat, white-pruinose 

 to dark brown, the exciple thick, entire to crenate, becoming sorediate; spores 

 oblong-ellipsoid, 25-35 X 12—18 /x. 



On mosses over rocks, soil, and trees, California and South Dakota. 



16. Physcia pulverulenta (Schreb.) Nyl., Act. Soc. Linn. Bord. 21:308. 1856. 

 Lichen pulverulentus Schreb., Spic. Fl. Lips. 128. 1771. P . pulverulenta var. 



leucoleiptes Tuck. P. pulverulenta var. pityrea (Ach.) Nyl. P. pulverulenta 

 var. angustata Nyl. P. pulverulenta var. argyphaea (Ach.) Nyl. 

 Thallus usually middle-sized to large, adnate, greenish gray to brown, usually 

 completely or interruptedly white-pruinose, the lobes narrow, sometimes elongated, 

 somewhat branched, the margins entire, crenate or rarely lobulate, sometimes as- 

 cending and powdery; brownish black to black below, lighter toward the margins, 

 with numerous brown to black rhizoids; apothecia rare, small to middle-sized, 2.5- 

 5 mm. across, sessile, the disk concave to flat, whitish pruinose to dark brown, 

 the exciple entire, crenate, or irregularly lobed; spores oblong-ellipsoid, 23-40 X 

 12-20 ft. 



On trees, old wood, rocks, and rarely on mosses, throughout the United States. 



