Guide to the Lichens of the New York Area — Part 8 



G. G. Nearing 



Group 8 — continued 



Physcia stellaris. Star Lichen 



Fairly common on trees and rocks throughout the New York 

 area. The small, but rather conspicuous and dainty rosettes, up 

 to 5 cm. across, lie rather flat, with regularly radiating branches 

 about 1 mm. wide, which are distinctly convex. The central parts 

 become a confused, warty mass. The color of the dull upper surface 

 is whitish or silvery gray to slate, darkening in the center. The 

 under surface is white or pale gray, with small, whitish root-like 

 holdfasts. 



Fruits usually many, often very plentiful, as much as 4 mm. 

 in diameter, but most of them commonly less than 2 mm. The flat 

 disk is dark brown or black, often frosted pale gray, the rim pale 

 gray, smooth, toothed or broken. Spores 2-celled, brown, 14 to 24 

 by 7 to 11 microns. 



Physcia stellaris, a well marked though variable lichen can be 

 distinguished by its pale gray color, and the absence of soredia in 

 any form. Smaller than most of the gray Shield Lichens (Groups 5 

 and 6), it is further distinguished by its dull surface. The puffed 

 Parmelias, especially P. colpodes, may resemble it superficially, 

 but all are black or dark brown beneath. P. centrijuga and P. am- 

 bigua both have a distinct yellow tint wholly lacking in Physcia 

 stellaris. Most other species of Physcia have soredia. Of those which 

 have not, P. adglutinata is small, dull, inconspicuous, with very 

 thin tips. P. tribacia has many white points on the tips and margins 

 and may have soredia. The only likely confusion is with P. alpolia, 

 a mere subspecies, separated by its broader lobes, with an under 

 surface and holdfasts which blacken. Doubtful specimens should 

 be called P. stellaris. 



Physcia aipolia 



Also called P. stellaris var. aipolia, or included in P. stellaris. 

 A subspecies differing but little. The tips tend to widen and raise 

 their thinnish margins slightly, in contrast to the turned-down 

 margins and thick tips of P. stellaris. The under surface and hold- 

 fasts of P. aipolia tend to blacken. Though the name is in use in the 



198 



