129. Rhizocarpon ] 33. LECIDEACEAE 239 



Thallus thin to moderately thick, smooth to rough, chinky to areolate, greenish 

 gray to ashy or becoming brownish black, continuous or scattered upon a black 

 hypothallus; apothecia small to middle-sized, 0.3-1.5 mm. across, partly immersed 

 to adnate, round to sometimes irregular and clustered, the disk flat to slightly 

 convex, blackish brown to black, the exciple thick, black, rarely whitish pruinose, 

 finally disappearing; hypothecium blackish brown; paraphyses semi-distinct; asci 

 clavate to inflated-clavate ; spores 8, hyaline to dark brown, oblong-ellipsoid, 3-7- 

 or rarely 9-septate transversely and 1-3-septate longitudinally, 16-40 X 8-18 /x. 



On rocks, and rarely on old wood, throughout northern United States, and 

 southward in the mountains. 



var. confervoides (DC.) Zahlbr., Cat. Lich. Univ. 4:388. 1926. 



R. confervoides DC, in Lam. & DC, El Fr. ed. 3. 2:366. 1815. 



Thallus moderately thick, brownish gray to brown, coarsely granulose, the 

 granules strongly convex, commonly scattered upon a conspicuous black hypothal- 

 lus; apothecia irregular, the disk commonly convex, the exciple seldom disappear- 

 ing. 



On rocks, Vermont. 



11. Rhizocarpon obscuratum (Ach.) Mass., Ric. Lich. 103. f. 207. 1852. 

 Lecidea petraea var. obscurata Ach., Lich. Univ. 156. 1810. R.petraeum var. 



obscuratum (Ach.) Krempelh. Lecidea panaeola var. obscurata (Ach.) 

 E. Fries. 



Thallus thin, grayish brown to ashy, minutely granulose, the granules flat, 

 continuous or rarely scattered on a poorly developed black hypothallus; apothecia 

 minute to small, 0.2-0.8 mm. across, partly immersed to adnate, the disk flat, 

 black, the exciple rather thick, black, becoming crenulate, rarely disappearing; 

 hypothecium blackish brown; asci inflated-clavate; spores 8, hyaline to brownish, 

 oblong-ellipsoid, 3-7-septate transversely and 1-3-septate longitudinally, 20-46 X 

 10-18 fi. 



On rocks, Maine and Minnesota. 



12. Rhizocarpon ambiguum (Schaer.) Zahlbr., Cat. Lich. Univ. 4:344. 1926. 

 Lecidea petraea var. ambigua Schaer., Lich. Helv. Spic. sec. 3. 137. 1828. R. 



dis tine turn T. Fries. 



Thallus thin, whitish to gray or brownish, minutely areolate or sometimes 

 warty, the areoles continuous or scattered upon a conspicuous black hypothallus; 

 apothecia small, 0.4-0.75 mm. across, adnate, the disk flat to convex, black, rough, 

 the exciple thin, slightly raised, finally disappearing; hypothecium dark brown; 

 asci clavate to inflated-clavate; spores 8, hyaline to brownish, oblong-ellipsoid, 

 5-7-septate transversely and 1-2-septate longitudinally, 21-36 X 11-16 /x. 



On rocks, Virginia and southern California. 



13. Rhizocarpon penichrum (Tuck.) Merrill; Millsp. & Nutt., Flora St. Catal. 



Island 367. 1923. 



Buellia oidalea var. penichra Tuck., Syn. N. A. Lich. 2:99, 100. 1888. Buellia 

 penichra (Tuck.) Hasse. 



Thallus thin, smooth to rough, becoming minutely areolate, ashy to whitish, 

 bordered and sometimes intersected by the black hypothallus; apothecia small to 

 middle-sized, 0.35-1 mm. across, sessile, the disk flat to slightly convex, dull black, 

 the exciple thick, black, somewhat raised, finally disappearing; hypothecium dark 

 brown; paraphyses semi-distinct, appearing to be branched; asci clavate to in- 

 flated-clavate; spores 6-8, brownish to dark brown, oblong to oblong-ellipsoid, 

 3-5-septate transversely and 1-2-septate longitudinally, 14-28 X 8-15 /x. 



On trees, Montana, Washington, and California. 



14. Rhizocarpon interponens (Nyl.) Zahlbr., Cat. Lich. Univ. 4:374. 1926. 

 Lecidea interponens Nyl., Lich. Lab. Sing. 42. 1891. 



Thallus very thin, ashy to gray, minutely granulose, the granules flat, contin- 

 uous or rarely scattered; apothecia minute, 0.2-0.5 mm. across, partly immersed 



