152 HERRE 



XXXVI. Placynthium (Ach.) Harm. 



Collema sect. Placynthium Ach. Lich. Univ. 628. 1810. 

 Placynthium Harm. Cat. Des. Lich. Lor. 1894. 



Thallus areolate-crustaceous, granular, coralloid, or of small 

 squamules, with a more or less well developed blue black hypo- 

 thallus; alga Scytonema. 



Apothecia sessile, lecideine or biatorine, plane or convex; hypo- 

 thecium clear or dark; paraphyses simple, septate, the tips thick- 

 ened and darker; spores colorless, elongate or ellipsoid-ovoid, 2-8 

 locular. 



Species few; obscure lichens of rocks, wood, and mosses. 



KEY TO SPECIES. 



A. Thallus more or less coralloid granulose, black .......... i. nigrum 



A A. Thallus of lobulate appressed squamules, deep brown. ..2. dubium 



i. PLACYNTHIUM NIGRUM (Huds.) S. Gray. 



Lichen niger Hudson, Fl. Angl. 2: 524. 1778. 

 Placynthium nigrum S. Gray, Nat. Arr. 1 : 395. 1821. 

 Pannaria nigra Nyl. Lich. Scand. 126. 1 86 1 . 

 Pannaria nigra Tuck. Syn. N. Am. Lich. 1:127. 1882. 



Thallus crustaceous, very minutely coralloid granulose or sub- 

 squamulose, areolate, scattered or continuous, rather thin; on a 

 thin black or bluish black hypothallus; color very dark, appearing 

 sooty black to the naked eye; specimens from other localities vary 

 from brownish black to dark grayish black and black. 



Apothecia minute to small, at first with plane, reddish black disk 

 and entire, thin margin, but soon much larger, convex, dead black, 

 the margin excluded and then lecideine; epithecium blackish green; 

 paraphyses rather stout, septate, their dark green tips enlarged; 

 hypothecium dark brown or blackening basally; thecium colorless, 

 blue with I; the pseudoparenchymatous tissue of the apothecial 

 wall violet with KOH; asci clavate; spores colorless, ellipsoid, bi- 

 locular or sometimes rather imperfectly 4-locular, 



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