48. Arthothelium ] 14. ARTHONIACEAE 93 



48. Arthothelium Mass., Ric. Lich. 54. f. 101. 1852. 



Thallus rudimentary, without cortical tissues, partly within the substratum and 

 forming a thin to thicker, uneven, areolate crust; apothecia small to large, round 

 to irregular, more or less immersed to adnate, the disk brownish black to black; 

 hypothecium brownish to dark brown; hymenium hyaline to brown; paraphyses 

 usually branched; asci pyriform; spores usually 8, hyaline to brownish, large, 

 transversely and longitudinally septate. 



The algal hosts are Trentepohlia and Palmella. 



A. Apothecia not black 1. A. sanguineum 



A. Apothecia black 



B. Spores rarely less than 9-septate transversely 

 C. Spores more than 40 /i in length 



D. Thallus ashy white to grayish ; apothecia 



0.4-1 mm. across 2. A. distendens 



D. Thallus yellowish ashy to whitish; apothecia 



0.6-3 mm. across 11. A. macrothecum 



C. Spores less than 40 fj. in length 10. A. albovirescens 



B. Spores rarely more than 7-septate transversely 

 C. Spores rarely more than 22 ft in length 

 D. Disk more or less whitish pruinose 



E. Apothecia 0.15-0.35 mm. across ... ... 5. A. pruinascens 



E. Apothecia 0.2-1.2 mm. across 7. A. anastomosans 



D. Disk black 8. A. abnorme 



C. Spores rarely less than 22 fi in length 

 D. Disk more or less whitish pruinose 



E. Apothecia 0.1-0.25 mm. across 9. A. taediosum 



E. Apothecia 0.3-1.5 mm. across 4. A. spectabile 



D. Disk brownish black to black 



E. Apothecia 0.4-0.8 mm. across 12. A. interveniens 



E. Apothecia not more than 0.5 mm. across 

 F. Thallus whitish to lead-gray or ashy white 

 G. Thallus bordered wholly or in part by 



a black line 13. A. Hallii 



G. Thallus not bordered by a black line . . . 6. A. orbilliferum 

 F. Thallus light greenish gray 3. A. subcyrtodes 



1. Arthothelium sanguineum (Willey) Zahlbr., in E. & P., Nat. Pfl. r:91. 1907. 

 Arthonia sanguined Willey, Syn. Arth. 22. 1890. 



Thallus very thin, white to pale yellowish white; apothecia small to middle- 

 sized, 0.35-1 mm. across, immersed to semi-superficial, round to oblong or slightly 

 irregular, the disk white-pruinose to dark reddish brown or finally blackening; 

 hyaline within; asci pyriform; spores hyaline or tinged brown, oblong-ovoid, 7-11- 

 septate transversely and 3-5-septate longitudinally, 20-32 X 12—18 ft. 



On trees, Santa Monica Range, California. 



2. Arthothelium distendens (Nyl.) Mull. Arg., Bull. Herb. Boiss. 2:736. 1894. 



Arthonia distendens Nyl., Ann. Sci. Nat. Bot. IV. 19:351. 1863. 



Superficial thallus thin, ashy white to grayish, smooth to rough and becoming 

 chinky; apothecia small to middle-sized, 0.4-1 mm. across, partly immersed to 

 adnate, round to more or less irregular, the disk flat, black; tinged pale 'yellowish 

 within; asci subglobose; spores hyaline, oblong-ellipsoid, sometimes slightly curved, 

 9-11-septate transversely and 1-4-septate longitudinally, 40-62 X 14-20 /x. 



On trees, Florida. 



3. Arthothelium subcyrtodes (Willey) Hasse, Bryologist 18:92. 1915. 



Arthonia subcyrtodes Willey, Int. Stud. Lich. Suppl. 54. 1887. 



Thallus thin, smooth, light greenish gray; apothecia minute to small, 0.1- 

 0.5 mm. across, immersed, round to commonly somewhat irregular, the disk flat 

 to convex, black; tinged brownish within; spores oblong-ellipsoid, hyaline to finally 

 brown, 5-7-septate transversely and 2-3-septate longitudinally, 20-25 X 7.5-10 ft. 



On trees, Santa Monica Range, California. 



