240 33. LECIDEACEAE [ 129. Rhizocarpon 



to adnate, numerous, sometimes crowded, the disk flat, dull black, the exciple 

 thick, black, becoming wavy; hypothecium dark brown; asci inflated-clavate ; 

 spores 8, hyaline to rarely brownish, oblong-ellipsoid, 3-7-septate transversely and 

 1-3-septate longitudinally, 20-36 X 8-14 p. 

 On rocks, Tennessee. 



15. Rhizocarpon albineum (Tuck.) Fink n. comb. 



Buellia petraea f. albinea Tuck., Syn. N. A. Lich. 2:102. 1888. R. petraeum f. 

 albineum (Tuck.) Zahlbr. 



Thallus moderately thick, chinky-areolate, whitish to ashy, the areoles flat, 

 rather large, commonly in dense groups upon a black hypothallus; apothecia small 

 to middle-sized, 0.35-1 mm. across, partly immersed to adnate, the disk flat to 

 convex, black, the exciple thin, black, finally disappearing; hypothecium dark 

 brown; asci clavate to inflated-clavate; spores 8, hyaline to dark brown, oblong- 

 ellipsoid, 3-7-septate transversely and 1-2-septate longitudinally, 21-26 X 10-15 /t. 



On rocks, from New England to Virginia, and in Indiana. 



16. Rhizocarpon concentricum (Davies) Beltr., Lich. Bass. 187. pi. 4, f. 9-12. 



1858. 



Lichen concentricus Davies, Trans. Linn. Soc. Lond. 2:284. 1794. R. calcareum 

 var. concentricum (Davies) T. Fries. R. sub concentricum (E. Fries) Koerb. 



Thallus thin, more or less circular, smooth to chinky and finally areolate, the 

 areoles minute, ashy to whitish, continuous; apothecia small to middle-sized, 0.3- 

 1.5 mm. across, partly immersed to adnate, commonly showing a well-defined con- 

 centric arrangement, the disk concave to slightly convex, dull black, rarely whitish 

 pruinose, the exciple rather thick, black, finally disappearing; hypothecium dark 

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

 to dark brown, 5-9-septate transversely and 2-3-septate longitudinally, 22-39 X 

 10-16 ix. (Plate 19 a.) 



On rocks, Alabama and Minnesota. 



17. Rhizocarpon athalloides (Nyl.) Hasse, Cont. U.S. Nat. Herb. 17:57. 1913. 

 Lecidea athalloides Nyl., Bull. Soc. Bot. France 7:503. 1860. 



Thallus dirty white to yellowish, composed of loosely interwoven hyphae, be- 

 coming minutely granulose, or continuous and finally becoming chinky; apothecia 

 small to middle-sized, 0.4-1.5 mm. across, partly immersed to adnate, the disk 

 flat to slightly convex, dull black, the exciple thin, black, obscurely crenulate, 

 finally disappearing; hypothecium brownish; asci clavate to inflated-clavate; spores 

 4-6, ovoid and sometimes pointed at one end, hyaline to brown, 3-5-septate trans- 

 versely and 1-3-septate longitudinally, 22-38 X 10-18 /a. 



On soil, mountains of southern California. 



18. Rhizocarpon viridiatrum (Wulf.) Koerb., Syst. Lich. 2o2. 1855. 

 Lichen viridiater Wulf., in Jacq., Coll. Bot. 2:186. 1788. 



Thallus granulose-areolate, greenish yellow, continuous or scattered upon an 

 inconspicuous black hypothallus; apothecia small, 0.4-0.8 mm. across, adnate to 

 subsessile, the disk flat to convex, rough, dull black, the exciple black, crenulate, 

 rarely disappearing; hypothecium dark brown; asci becoming inflated-clavate; 

 spores 8, dark brown, fusiform to ellipsoid, 3-septate transversely and 1 -septate 

 longitudinally, 18-25 X 8-11 p. 



On rocks and boulders, California. 



19. Rhizocarpon lecanorinum (Koerb.) Anders, Hedwigia 64:261. 1923. 



R. geographicum var. lecanorinum Koerb., Syst. Lich. 263. 1855. Buellia geo- 



graphica var. lecanorina (Koerb.) Tuck. R. geographicum f. lecanora 



(Floerke) Arn. 



Thallus thin, greenish to bright yellow, becoming areolate, the areoles small, 



slightly raised, usually scattered upon a conspicuous black hypothallus; apothecia 



