165 



flat rosettes very variable in shape and size, Inil often 10 cm. or 

 more across, and with branches up to 7 or 8 mm. wide, though 

 usually much narrower. The sul)stance is thin, and the margins may 

 curl upward slightly, especially in much wrinkled forms. The 

 shining greenish gray upper surface is wrinkled in a net-like pat- 

 tern, with shallow pits between the raised wrinkles. Brownish 

 granules are often strewn along these wrinkles, and in var. fur- 

 furacca they lengthen into minute prongs or coral-like growths, 

 often massed all over the center of the lichen. The under surface 

 is black, with many short, black, root-like holdfasts, often dense 

 to the very tip. 



Fruits, not often seen, are deeply saucer-shaped, chestnut- 

 brown, with a rim often roughened and warty. Spores undivided, 

 colorless, 10 to 20 by 7 to 12 microns. 



PanncUa saxatilis is one of the few rosette lichens with a net- 

 like pattern of pits and wrinkles, and though this marking may 

 be faint, it usually serves to distinguish the species from all others, 

 for the pitted members of Cetraria (Group 4) and Sticta (Group 

 7) tend to raise at least their tips free from the footholds, while 

 P. saxatilis usually lies flat. The other typically pitted lichens 

 also have the under surface pale in contrast with the black of this 

 species and its conspicuous black holdfasts. Though var. furfiira- 

 cea may look at first glance like the paler Cetraria aleurites (Group 

 5), the black under surface will distinguish it at once. The most 

 likely confusion is with P. suhlacvigata, a subspecies of P. tiliacca 

 in some respects intermediate between the two species. Typical 

 P. tiliacea, which has the margins curled downward, and parallel 

 wrinkles across the larger trunks, and which commonly bears 

 many fruits, could hardly be mistaken for typical P. saxatilis, but 

 intermediate forms between these two common lichens are some- 

 times difficult to name, and the invention of a subspecies, as usual 

 in such cases, only increases the difficulty, making two series of 

 intermediates in place of one. P. Borrcri and P. rudecta sometimes 

 appear slightly pitted, but can be distinguished by their larger 

 size, flat, round, white soredia rather regularly studded over the 

 upper surface, and by the under surface being brown rather than 

 black. P. omphalodes, a small, brown form of P. saxatilis growing 

 on rocks in the north, need not be described here because it does 

 not occur in the New York area. 



