236 33. LECIDEACEAE [ 129. Rhizocarpon 



7. Lopadium phyllocharis (Mont.) Fink n. comb. 



Biatora phyllocharis Mont., Ann. Sci. Nat. Bot. III. 10:128. 1848. Heterothe- 

 cium phyllocharis (Mont.) Tuck. Sporopodium phyllocharis (Mont.) Mass. 



Thallus very thin, smooth or slightly granulose, greenish gray, usually in small 

 areas; apothecia minute, 0.25-O.S mm. across, sessile, the disk convex, pale brown- 

 ish varying toward greenish, finally black, the exciple thin, white, soon disappear- 

 ing; hypothecium brownish; spores 1, oblong-ellipsoid, 11-29-septate transversely 

 and 2-5-septate longitudinally, 30-75 X 12-36 jx. 



On leaves, Alabama and Florida. 



129. Rhizocarpon Lam., in Lam. & DC, Fl. Franc, ed. 3. 2:365. 1815. 



Thallus crustose to subsquamulose, commonly areolate or warty, not distinctly 

 differentiated and attached to the substratum by hyphal rhizoids; apothecia cir- 

 cular or flexuous, immersed to sessile, the disk flat to convex, usually black, the 

 exciple colored like the disk, usually disappearing; hypothecium brown to blackish 

 brown; hymenium hyaline to brownish above; paraphyses unbranched or branched; 

 asci clavate to inflated-clavate; spores 1-8, large, hyaline to more commonly 

 brown, transversely and longitudinally septate. 



The algal host is Pleurococcus. 



A. Spores transversely septate and sometimes becoming 

 longitudinally septate 

 B. Spores transversely septate 

 C. Spores 3-septate 



D. Spores 14-18 X 5-7 /t 3. R. vernicomoideum 



D. Spores 16-26 X 7-12 fi 2. R.Oederi 



C. Spores 1-septate .... 1. R. alpicolum 



B. Spores transversely and becoming longitudinally septate 



C. Thallus ashy gray to white, sometimes circular . . . . 6. R. alboatrum 

 C. Thallus ashy to grayish brown, more or less irregular 



D. Thallus thin, sometimes disappearing 4. R. postumum 



D. Thallus thin, bordered and intersected by a 



black hypothallus 5. R. cinereovirens 



A. Spores transversely and longitudinally septate 



B. Thallus greenish gray, ashy to whitish or brownish 

 to rarely black 



C. Spores rarely more than 40 fi in length 

 D. Thallus smooth to chinky or areolate 



E. Spores rarely more than 25 fi in length 



F. On trees; thallus thin 13. R. penichrum 



F. On rocks; thallus moderately thick 15. R. albineum 



E. Spores commonly more than 25 fi in length 

 F. Apothecia irregularly arranged 



G. Thallus thin to moderately thick; apothecia 

 0.3-1.5 mm. across 

 H. Thallus smooth or chinky to areolate, 



greenish gray to ashy or brownish black . . 10. R. petraeum 

 H. Thallus areolate, ashy to purplish or 



brownish 9. R. grande 



G. Thallus thin; apothecia 0.4-0.75 mm. across . . 12. R. ambiguum 

 F. Apothecia concentrically arranged .... 16. R concentricum 

 D. Thallus minutely to coarsely granulose 



E. Thallus minutely granulose, ashy or grayish brown 

 to ashy 

 F. Apothecia 0.2-0.5 mm. across; spores 



20-36 X 8-14 /x 14. R. interponens 



F. Apothecia 0.2-0.8 mm. across; spores 



20-46 X10-18m 11. R. obscuratum 



E. Thallus coarsely granulose, brownish gray to 



brown 10. R. petraeum confervoides 



C. Spores commonly more than 40 /j. in length 



D. Thallus areolate or warty, ashy gray to reddish or 



brownish 7. R. disporum 



