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Pan>iclia conspcrsa. Bouldf-r Lichen 



The most frequent and cons])icuous of all lichens that grow 

 on stone. Seen on boulders, stone fences, cliffs, and occasionally 

 the roots of trees, in shade or full sun. In size it varies from 

 dwarfed rosettes 4 or 5 cm. across, with parts hardly more than 

 1 mm. wide, to mats that spread a meter or more over the rock, 

 with little to show whether it is all a single lichen reviving again 

 where old and broken, or a number of lichens tangled together. 

 The humped branches grow over each other shingle-fashion, and 

 may end in blunt lobes more than 5 mm. wide, or more commonly 

 divide into many narrowed and pointed tips. So tangled and con- 

 fused are the parts that the trunks cannot usually be traced or 

 measured. There may be abundant fruits or none. Nearly the whole 

 lichen may be lost under dense coral-like growths 2 or 3 mm. 

 high. Or the lichen may be reduced to a few straggling uncon- 

 nected tips scattered over the rock. 



The upper surface has nearly always a yellowish tint toward 

 the tips, which are pale, but the older central parts may blacken 

 or turn olive-green, or sometimes burn brownish in the sun. The 

 tips are usually pale yellowish or greenish, smooth and shining. 

 The under surface, commonly brown, but sometimes turning 

 brownish black, shows a few dark, root-like holdfasts. 



Fruits, often many and crowded, are saucer-shape, up to 

 12 mm. across, dark brown, purplish or greenish, the rims nearly 

 smooth or toothed. Spores undivided, colorless, 8 to 12 by 4 to 7 

 microns. 



If you glance at a rock covered with Papery Lichen and say 

 it is P. conspersa, you will be right most of the time, because this 

 species is common everywhere. On closer examination, the char- 

 acters to remember are shining, pale yellowish tips which mostly 

 turn downward and touch the rock ; also a brown under surface 

 with comparatively few holdfasts. P. caperata has similar color- 

 ing, but the upper surface, instead of shining, has a texture like 

 kid leather, the lobes are much broader, the tips wavy margined, 

 not pointed, and instead of the coral-like growths, it has small 

 warts dusty with yellowish soredia. P. saxatilis and P. tiliacca are 

 distinct in their lack of any yellow tint, and in their black, rather 

 than brown under surface, with many black holdfasts. P. Borreri 

 and P. rudccta also occasionally grow on rocks. They are dis- 



