46 4. PYRENULACEAE [ 15. Arthopyrenia 



obliquely uniseriate, or irregularly arranged, the cells cylindrical or almost cubical, 

 sometimes unequal. 



The algal host is Trentepohlia. 



A. On rocks 



B. Spores constantly 1 -septate 



C. Perithecia less than 0.3 mm. across 



D. Thallus smooth, grayish; spores 13-20 X 5-8 /* .... 4. A. litoralis 

 D. Thallus smooth to chinky or areolate, greenish brown 



or blackish; spores 12-15 X 4.5-7 m 5. A. halodytes 



C. Perithecia 0.3-0.7 mm. across 12. A. conoidea 



B. Spores becoming 2- and 3-septate 

 C. Thallus grayish to ashy 



D. Spores 10-14 X 5-6 fi 17. A. dimidiata 



D. Spores 14-21 X 5-7 n 16. A.distans 



C. Thallus tinged rose-colored 14. A. prospersella 



A. On trees 



B. Spores constantly 1 -septate 



C. Perithecia less than 0.3 mm. across 



D. Thallus usually indicated by a coloration of the substratum 



E. Thallus whitish; spores 11-16 X 3-5.5 /* 3. A. subprostans 



E. Thallus light gray; spores 12-16 X 5-7 m 1. A. biformis 



D. Thallus usually in small, ashy gray patches 2. A. parvula 



C. Perithecia usually more than 0.3 mm. across 



D. Thallus usually indicated by a coloration of the substratum 



E. Spores 32-60 n in length 8. A. Finkii 



E. Spores less than 30 m in length 



F. Thallus somewhat powdery, whitish to ashy gray; 



spores 12-22 X 7-13 /x 9. A. alba 



F. Thallus smooth, grayish or brownish gray; 



spores 16-25 X 5-7.5 /i 6. A. epidermidis 



D. Thallus very thin, usually persistent 



E. Perithecia apparently pruinose .... . 7. A. cinereopruinosa 



E. Perithecia not pruinose 



F. Spores 14-21 X 5-7 m ... 11. A. leucochlora 



F. Spores 16-25 X 6-8 fi 10. A. analepta 



B. Spores 1-3- or more-septate 

 C. Spores 1-3-septate 



D. Spores more than 16 /x in length 



E. Perithecia 0.25-0.3 mm. across 13. A. rhyponta 



E. Perithecia larger, reaching 0.5-0.8 mm. across 



F. Thallus whitish 19. A. Cinchonae 



F. Thallus ashy gray to brownish 



G. Ostiole punctiform 18. A. punctiformis 



G. Ostiole round 20. A. Cerasi 



D. Spores 9-16 X 3.5-5.5 fi 15. A. conformis 



C. Spores more than 3-septate 



D. Spores 3-5-septate 21. A. hyalospora 



D. Spores 5-7-septate 22. A. quinqueseptata 



1. Arthopyrenia biformis (Borr.) Mass., Framm. Lich. 26. 1855. 



Verrucaria biformis Borr., in Sowerby, Engl. Bot. Suppl. 1: pi. 2617. 1831. 



Thallus thin, smooth, light gray or disappearing superficially and indicated by 

 a widespread, light gray area; perithecia minute, 0.1-0.2 mm. across, the superficial 

 portion convex, black, the wall dimidiate, the ostiole indicated by a whitish area; 

 spores obliquely uniseriate, 1-septate, ellipsoid, 12-16 X 5-7 /x. 



On trees, Maine, Florida, and California. 



2. Arthopyrenia parvula Zahlbr., Beih. Bot. Centralb. 13:149,150. 1902. 

 Superficial thallus usually in small patches, thin, smooth, ashy gray; perithecia 



minute, 0.08-0.12 mm. across, superficial portion hemispherical, black, the wall 

 thin, complete, black, the apex becoming depressed, the ostiole punctiform; spores 

 1-septate, ellipsoid, 15-17 X 5-7 /a, uniseriately arranged. 

 On trees, Santa Monica Range, California. 



