172 30. PANNARIACEAE [110. Placynthium 



hypothecium hyaline to brown; hymenium hyaline or bluish brown above; paxaph- 

 yses unbranched; asci clavate; spores 8, hyaline, oblong to oblong-ellipsoid or 

 ellipsoid, 1-3-septate. 



The algal host is Scytonema. 



A. Spores 1-septate 4. P. stenophylla 



A. Spores 1-3-septate 



B. Thallus of minute squamules, passing into a thin, granulose crust 



C. Thallus lead-ashy 1. P. nigrum 



C. Thallus dark gray to ashy white 1. P. nigrum caesium 



B. Thallus more or less distinctly squamulose, the 

 squamules more or less lobed 

 C. The squamules sometimes covered with coralloid branchlets, 



the lobes narrow, much divided 3. P. flabellosum 



C. The squamules irregularly lobed, the lobes entire . . 2. P. microphyllizum 



1. Placynthium nigrum (Huds.) S. F. Gray, Nat. Arr. Brit. PI. 1:395. 1821. 

 Lichen niger Huds., Flora Angl. II. 2:524. 1778. Pannaria nigra (Huds.) Nyl. 

 Thallus composed of minute, lead-ashy, scattered and lobed squamules, or 



more often the squamules heaped into a thin, broken, granulose crust, on a thin, 

 bluish black hypothallus; apothecia minute to small, 0.2-0.6 mm. across, sessile, 

 the disk flat to convex, reddish brown to more commonly black, the proper exciple 

 thin, brownish black to black, soon disappearing; hypothecium brownish to brown; 

 hymenium hyaline below to bluish brown toward the top; spores oblong, 1-3- 

 septate, 11-16 X 4.5-7 fi. 



On rocks, throughout northern United States. 



var. caesium (Schaer. ) Hue, Bull. Soc. Linn. Normand. V. 9:146. 1906. 

 Lecidea triptophylla var. caesia Schaer., Enum. Lich. Eur. 99. 1850. (pr. p.) 



Pannaria nigra var. caesia (Schaer.) Malbr. 

 Thallus dark gray to ashy white. 

 On calcareous rocks, New York and Iowa. 



2. Placynthium microphyllizum (Nyl.) Hasse, Cont. U.S. Nat. Herb. 17 ] :81. 



1913. 



Pannularia micro phylliza Nyl.; Hasse, Lich. South. Calif. 9. 1898. 



Thallus thin, composed of small, dark yellowish brown to cervine brown, closely 

 clustered, irregularly somewhat lobed, marginally ascending squamules; pale below; 

 apothecia small to middle-sized, 0.4-0.8 mm. across, sessile, the disk slightly con- 

 cave to convex, dark reddish brown, the proper exciple thin, lighter colored than 

 the disk, finally disappearing; hypothecium hyaline to yellowish; asci inflated- 

 clavate; spores long-ellipsoid, 1-3-septate, 16-28 X 6-9 /a. 



On rocks, southern California. 



3. Placynthium flabellosum (Tuck.) Zahlbr., Cat. Lich. Univ. 3:22 7. 192 5. 

 Pannaria flabellosa Tuck., Proc. Am. Acad. 5:401. 1862. 



Thallus thin, composed of small, pale lead-colored to ashy, irregularly lobed 

 squamules, sometimes covered with coralloid branchlets, the lobes narrow, 

 elongated, much divided, longitudinally striate and expanded toward the circum- 

 ference, round and heaped toward the center, on an indistinct, bluish black hypo- 

 thallus; apothecia minute to small, 0.2-0.4 mm. across, partly immersed to closely 

 adnate, the disk flat to slightly convex, reddish brown to black, the proper exciple 

 thin, becoming black, and rarely disappearing; spores oblong-ellipsoid, 1-3-septate, 

 16-20 X 5-7 ix. 



On granite rocks, New Hampshire, Vermont, and Minnesota. 



4. Placynthium stenophylla (Tuck.) Fink n. comb. 



Pannaria stenophylla Tuck., Proc. Am. Acad. 12:169. 1877. Parmeliella steno- 

 phylla (Tuck.) Zahlbr. 

 Thallus minute, round and stellate, greenish brown, the lobes round, branched 

 toward the circumference, becoming squamulose or granulose, and sometimes dying 



