238 ZS. LECIDEACEAE [ 129. Rhizocarpon 



to small, 0.3-0.7 mm. across, partly immersed to adnate, sometimes clustered, the 

 disk flat to slightly convex, dull black, the exciple thin, black, becoming flexuous, 

 finally disappearing; hypothecium dark brown; spores 8, hyaline to brown, 1-3- 

 septate transversely and becoming 1-septate longitudinally, 14-20 X 6-11 /x. 

 On rocks, Minnesota. 



6. Rhizocarpon alboatrum (Hoffm.) Anzi, Cat. Lich. Sondr. 92. 1860. 



Lichen alboater Hoffm., Enum. Lich. Icon. 30. 1784. Buellia alboatra var. 

 ambigua (Ach.) T. Fries. R. alboatrum f. saxicola (E. Fries) Fink. Lecidea 

 alboatrum var. epipolia (Ach.) Schaer. 



Thallus smooth, or chinky to warty-areolate, sometimes becoming powdery, 

 ashy gray to white, continuous or sometimes scattered; apothecia small to middle- 

 sized, 0.3 5-1 mm. across, immersed to adnate, the disk flat to convex, dull black 

 or whitish pruinose, the exciple thin, black, finally disappearing; hypothecium dark 

 brown; asci clavate; spores 8, brown, oblong-ellipsoid, 3-4-septate transversely 

 and becoming 1-2-septate longitudinally, 12-22 X 6-9 /a. 



On trees and rocks, throughout the United States; when on rocks, the thallus 

 is more circular and commonly bordered by a blackish hypothallus. 



7. Rhizocarpon disporum (Naeg.) Mull. Arg., Revue Mycolog. 1:170. 1879. 

 Lecidea dispora Naeg., in Hepp, Flecht. Eur. 28. 1853. R. geminatum Koerb. 



R. disporum var. Montagnei (Flot.) Zahlbr. Buellia Montagnei (Flot.) 

 Tuck. Buellia petraea var. Montagnei (Flot.) Willey. R. petraeum var. 

 Montagnei (Flot.) Boist. 

 Thallus thin to moderately thick, ashy gray to reddish or brownish, becoming 

 areolate or warty, continuous or scattered upon a black hypothallus; apothecia 

 small, 0.4-0.8 mm. across, subsessile, the disk flat to slightly convex, black, the 

 exciple thin, black, rarely disappearing; hypothecium dark brown; asci inflated- 

 clavate; spores 1 or rarely 2, hyaline to dark brown, ellipsoid to oblong-ellipsoid, 

 7-13-septate transversely and 3-5-septate longitudinally, 28-60 X 10-30 /x. 

 On rocks, throughout northern United States; also Florida and California. 



8. Rhizocarpon Bolanderi (Tuck.) Herre, Proc. Wash. Acad. Sci. 12:106. 1910. 



Buellia Bolanderi Tuck., Gen. Lich. 189. 1872. Buellia Bolanderi var. sulphurosa 

 Tuck. R. Bolanderi var. sulphurosa (Tuck.) Zahlbr. 



Thallus chestnut-brown to black, becoming squamulose, the squamules small, 

 adnate to sessile, becoming wavy or lobed, the margins ascending and black below, 

 sometimes sulphur-colored within, commonly scattered upon a black hypothallus; 

 apothecia small to middle-sized, 0.35-1.2 mm. across, adnate to sessile, the disk 

 flat to convex, dull black, the exciple thick, black, wavy, finally disappearing; 

 hypothecium dark brown; asci inflated-clavate ; spores 2, ellipsoid, hyaline to 

 grayish and dark brown, 7-1 1-septate transversely and 2-4-septate longitudinally, 

 with a dense halo, 30-72 X 18-34 /a. 



On rocks, Washington, Oregon, and California. 



9. Rhizocarpon grande (Floerke) Arn., Flora 54:149. 1871. 



Lecidea petraea var. ftiscoatra f. grandis Floerke; Flot., Flora 11:690. 1828. 

 Buellia petraea var. grandis (Floerke) Tuck. R. petraeum var. grande 

 (Floerke) Fink. 



Thallus thin to moderately thick, areolate, the areoles small, convex, ashy to 

 purplish or brownish, commonly scattered upon a conspicuous black hypothallus; 

 apothecia small to middle-sized, 0.4-1.1 mm. across, the disk convex to subglobose, 

 black, the exciple thin, black, soon disappearing; hypothecium dark brown; asci 

 clavate or inflated-clavate; spores 8, hyaline to blackish brown, oblong-ellipsoid, 

 3-7-septate transversely and 1-3-septate longitudinally, 25-42 X 12-20 /a. 



On rocks, throughout northern United States, and southward in the mountains. 



10. Rhizocarpon petraeum (Wulf.) Mass., Ric. Lich. 102. f . 206. 1852. 

 Lichen petraeus Wulf., Ges. Naturf. Fr. Bed. 2:89. 1788. Buellia petraea 



(Wulf.) Branth & Rostr. Buellia petraea var. vulgaris Tuck. R. eupetraeum 

 (Nyl.) Arn. 



