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Paniiclia tiliucca. Linden Lichen 



Also called P. qncrcina. An extremely variable lichen found 

 commonly on trees and occasionally on rocks, anywhere that 

 lichens grow, but i)articularly abundant in swamps. It forms tyi)ic- 

 ally flat rosettes, which may reach 10 cm. or more across. The 

 trunks are often thickened, slightly arched, and crossed by warty 

 wrinkles. The manner of branching varies greatly. 1)ut often 

 where two lobes meet, their sides touch or overlap slightly, while 

 the sinus between them may show as an almost circular oj^ening, 

 a pattern topical of few other lichens. Lobes may be wider than 

 5 mm. or much narrower, and some forms are so small that they 

 might belong with the Smaller Shield Lichens (Group 5). The 

 upper surface is greenish or bluish gray, the under is black, often 

 dark brown near the margins, with many short, black, root-like 

 holdfasts. 



Fruits are usually abundant, up to 12 mm. in diameter, irregu- 

 larly saucer-shaped, chestnut to ocher-brown, usually shining, with 

 a thin, smooth to broken or toothed rim. Spores undivided, color- 

 less. 5 to 11 by 4 to 7 microns. 



Most of the small or medium sized Shield Lichens found on 

 trees (these must not be confused with the still smaller and rather 

 more common Blister Lichens, Group 8) are either Parmelia 

 tiliacea or P. saxatilis. The many black holdfasts on the black 

 under surface of both these species distinguish them at once from 

 all the Smaller Shield Lichens except their own subspecies. The 

 puffed forms, P. physodes and P. colpodes (Group 5), are suffi- 

 ciently distinguished by their puffed or thickened tips, and though 

 black beneath, have few holdfasts. The Larger Shield Lichens also 

 fail to show any species with comparable abundance of black hold- 

 fasts, except P. perforata and its subspecies, which are much 

 larger, with raised tips and black, marginal hairs. The Blister 

 Lichens (Physcia, Group 8) have mostly small, blackish or gray 

 fruits, and dark 2-celled spores. 



The most important character for separating P. tiliacea from 

 P. saxatilis is the absence of any regular pitted pattern on the upper 

 surface of P. tiliacea. The branches of P. tiliacea are also shorter 

 and broader, with a tendency to progress in wave-like humps rather 

 than stay flat, but the small form called P. suhlaevigata spreads 

 in long, flat, fern-like branches which, unless fruited, somewhat 



