100 



recently been placed together in the genus Parmeliopsis, but it 

 seems simpler to follow the older tradition, omitting this new 

 genus. 



Cetraria placorodia. Plate Lichen. 



Also called Cetraria aleurites var. placorodia or Parmeliopsis 

 placorodia. Resembles C. aleurites in color and size, but does not 

 develop the central growths and does usually fruit. It is fairly 

 common in the pine barrens, where it may either grow flat on 

 the bark or wood, or may reach out its fan-like tips as much as 

 1 cm. from the foothold, especially when found on twigs. 

 Branches of nearly uniform width, about 1 mm., radiate side by 

 side, not usually overlapping. The upper surface tends to be 

 more gray or even greenish than the nearly white C. aleurites. 



Fruits, up to 7 mm. diameter or larger, stand near the center 

 of the lichen, raised 1 mm. or so, the disk round or becoming ir- 

 regular with age, yellowish gray, later green or brown. The rim 

 may be nearly smooth or broken with radiating ridges or 

 toothed. Spores undivided, colorless 4 to 9 by 3 to 6 microns. 



Cetraria placorodia resembles somewhat the larger Parmelia 

 tiliacea, which is rather common in swamps, but has a black 

 under surface and constantly chestnut-brown fruits. The yel- 

 low-gray fruits of C. placorodia distinguish it from most other 

 Shield Lichens except Parmelia ambigua, the upper surface of 

 which is distinctly yellowish, the under-surface black. Lecanora 

 muralis (Group 13) has fruits of this color, but grows only on 

 rocks. Confusion is likely with Physcia stellaris and P. tribacia 

 (Group 8), both of comparable size and growing in similar 

 places, but with fruits black or gray dusted with white, and 

 lacking any trace of yellow tint; spores 2-celled and blackish. 



Parmelia ambigua. Sulphur-Dust Lichen. 



Also called Parmeliopsis ambigua. Like Cetraria placorodia 

 this little lichen frequents the pine barrens, but only in the form 

 of its variety Halei, the species itself being found in the moun- 

 tains to the north, outside the New York area. The variety 

 spreads in oval rosettes 3 or 4 cm. across, usually on pine or 

 white cedar bark, either clinging flat or rising somewhat from 

 the foothold. Sometimes it wanders irregularly among other 

 lichens in fans up to 1 cm. wide, divided gracefully into regularly 



