174. Physcia ] 44. PHYSCIACEAE 385 



2. Physcia teretiuscula (Ach.) Lynge, Vid. Skrif. Math.-nat. Klasse. 96. 1916. 

 Parmelia caesia var. teretiuscula Ach., Lich. Univ. 479. 1810. P. caesia var. 



teretiuscula (Ach.) Nyl. 



Thallus small, closely adnate, light greenish gray, rarely sorediate, the lobes 

 somewhat round, elongated, much branched, sometimes imbricated, the margins 

 entire to crenate; pale below with pale to light brown rhizoids; apothecia small, 

 1-2 mm. across, sessile, the disk slightly concave to flat, dark brown to dull black, 

 the exciple entire to subentire; spores oblong-ellipsoid, 12-17X6-9/*. 



On rocks, Minnesota, Iowa, and North Dakota. 



Often confused with P. caesia (Hoffm.) Hampe, though quite different. 



3. Physcia caesia (Hoffm.) Hampe; Furn., Nat. Top. Regen. 2:250. 1839. 

 Lichen caesius Hoffm., Enum. Lich. Icon. 65. pi. 12, f. 1. 1788. Parmelia caesia 



var. stellata Tuck. 



Thallus middle-sized, adnate, light greenish gray to ashy, bearing round gray 

 soredia, the lobes usually quite elongated and branched, sometimes imbricated, the 

 margins entire to crenate; whitish below or rarely blackening, with usually dark 

 rhizoids; apothecia infrequent, small, 1.5-4 mm. across, sessile, the disk slightly 

 concave to flat, dark brown to black or rarely gray-pruinose, the exciple inflexed, 

 entire to crenulate; spores oblong-ellipsoid, 15-22 X 8-12 jx. 



On rocks and rarely on trees, northeastern United States, westward to the 

 Rocky Mountains. 



4. Physcia astroidea (Clem.) Nyl., Act. Soc. Linn. Bord. 21:308. 1856. 

 Parmelia astroidea Clem., Essai Sob. Veg. And. 302. 1807. 



Thallus thin, irregular to round, adnate, grayish white, the lobes narrow, flat- 

 tened, much branched with crenate margins, becoming granulose toward the center 

 or passing into finally massed soredia; whitish below with short blackening rhi- 

 zoids; apothecia small, 0.8-1.5 mm. across, closely sessile, the disk concave to flat, 

 black, sometimes pruinose, the exciple thin, colored like the thallus, becoming wavy 

 and curved inward; spores oblong-ellipsoid, 17-25 X 7-11 /x. 



On trees and rocks, New England, and southward to Florida and Texas. 



5. Physcia virella (Ach.) Flagey, Rev. Myc. 13:110. 1891. 



Lichen virellus Ach., Lich. Suec. 108, 109. 1798. P.obscura var. virella (Ach.) 

 T. Fries. 



Thallus small, closely attached to the substratum or ascending toward the 

 margins, grayish, greenish, or varying toward brown, the lobes short, closely packed 

 and often imbricate, plane or convex, crenately branched, with marginal and often 

 dorsal whitish to grayish green soredia; dark below, with short, black, usually 

 unbranched rhizoids; apothecia small, 1—1.5 mm. across, sessile, the disk flat, reddish 

 to dark brown, the exciple raised, of same color as the thallus and more or less 

 plainly hispid, at least below; spores oblong-ellipsoid, 15-25 X 7.5-12 fi. 



On trees, Michigan (no doubt more widely distributed, but no other specimens 

 studied belong here). 



6. Physcia obscura (Ehrh.) Hampe; Furn., Nat. Top. Regen. 2:249. 1839. 

 Parmelia obscura Ehrh., Plant. Crypt. Exsicc. 177. 1785. P.obscura var. 



ulothrix (Ach.) E. Fries. P. obscura var. ulothricoides Nyl. P. obscura var. 



muscicola (Schaer.) T. Fries. 

 Thallus middle-sized, adnate, smooth or rarely rough, greenish gray to brown 

 or ashy, rarely sorediate, the lobes commonly long and subdichotomously branched, 

 often imbricated, the margins round to crenate, rarely ciliate, often passing toward 

 the center into a subcrustose condition; black or rarely lighter below with rhi- 

 zoids of the same colors ; apothecia middle-sized to large, 0.8-4 mm. across, sessile, 

 the disk concave to slightly convex, reddish brown to black, the exciple entire to 

 crenulate, more or less hispid, at least below; spores oblong to ellipsoid, 15-27 X 

 8.5-12 fx. 



On trees, wood, rocks, and mosses, throughout the United States. 



