— 73 — 



Cetraria aleurites var. placorodia Tuck. Syn. N. A. Lich. 1: 32. 1882. 

 Thallus orbicular, 1.5-3 cm. in diameter, thicker, more ascendant, and 

 less closely adherent than in the other species; whitish to cinereous above, smooth 

 at the circumference, rugose toward the center; never isidiose or sorediate; be- 

 neath whitish, with a few pale rhizoids; lobes 1-2 mm. wide, more or less regu- 

 larly radiate, the tips sinuate-pinnatifid. Upper cortex 15-25/i thick, loosely 

 and irregularly pseudoparenchymatous with thick- walled cells, io-i2/x in out- 

 side diameter, the lumina 3-6/x in diameter; lower cortex 15-30^1 thick, well- 

 developed, compact, and chondroid, the divisions between the cell-walls not 

 visible, the lumina 2-4^1 or rarely up to 6^1 in diameter. Apothecia usually num- 

 erous, elevated, 1-8 mm., mostly 3 mm., in diameter; disk fulvous to badious,^ 

 flat or concave; thalline margin crenate, thin, often involute. Spores broadly 

 ellipsoid, 5-9X3-5M- Spermagonia frequent, occurring in the form of conspic- 

 uous, shining black tubercles. 



Specimens examined from: Massachusetts (8 towns), Rhode Island, New Jersey, 



Maryland, District of Columbia. 

 Exsiccati: Tuckerman's Lich. Amer. Sept. No. 71. Decades N. A. L. No. 280. 



Lich. Bor. Am. No. 210. Merrill's Lich. Exs. No. 144. 

 Parmeliopsis placorodia differs from the other species of the genus in the 

 absence of isidia and soredia. From all species of Parmelia it can be distinguished 

 by the whitish, sparingly fibrillose, under side; from Cetraria by the color com- 

 bined with the relatively narrow, radiate lobes. 



2. Parmeliopsis aleurites (Ach.) Nyl. 



Lichen Ach. Lich. Prodr. 117. 1798. 



Parmeliopsis Nyl. Not. Sallsk. pro F. et Fl. Fenn. Forh. n. s. 5: 121. 



1866. as to nomenclature but not as to characters or plant! 

 Cetraria aleurites Th. Fr. Lich. Scand. 109. 1871. Tuck. Syn. N. A. L. 



1: 32. 1882. 



Parmeliopsis placorodia Nyl. according to specimens in the Mus. d'Hist. 

 Nat. Paris! 



Platysma diffusum Nyl. Flora 55: 247. 1872. Crombie Brit. Lich. 1: 

 222, 1894, according to specimens in the British Museum! Not Lichen 

 diffusus Weber. 



Parmelia obsessa Ach. Syn. Lich. 213. 18 14. according to type-specimen 

 in the Botanical Museum, Helsingfors. Not Parmelia obsessa Mont. 

 Thallus orbicular, mostly 2-4 cm. in diameter, closely adherent to the sub- 

 stratum, whitish to cinereous or even fuscescent above, smooth at the circum- 

 ference, otherwise densely covered with closely packed isidia; in old specimens 

 the center becoming cracked, rimose-areolate and subcrustose, the isidia some- 

 times appearing white from abrasion, but the plant never sorediate; beneath 

 whitish and rugose, with a few pale rhizoids. Lobes and anatomical structure 

 as in P. placorodia. Apothecia rare, when present sometimes reaching 6 mm. 

 in diameter, but usually 2-3 mm.; disk badious, concave; thalline margin crenate, 



According to color-chart in Saccardo's Chromotaxia. 



