350 
OHIO BIOLOGICAL SURVEY 
KEY TO THE SPECIES OF RHIZOCARPON 
On bark.2. R. alboatrum 
On rocks. 
Spores smaller and 4-celled .1. R. vernicomoideum 
Spores larger and becoming muriform.3. R. petraeum 
1. Rhizocarpon vernicomoideum sp. nov. 
Thallus of minute, rounded, scattered or sometimes clustered, straw- 
colored granules, covering small areas, and usually resting on and limited 
wholly or in part by a black hypothallus; apothecia minute to small, 0.2 to 0.6 
mm. in diameter, black, semi-immersed to adnate, at first flat with a thin 
somewhat raised exciple, becoming convex with the exciple finally covered; 
hypothecium brown; hymenium pale or tinged brown below and light 
brown above; paraphyses coherent, distinct or semi-distinct; asci clavate; 
spores brown, 4-celled, becoming slightly constricted at the septa, 15 to 18 
mic. long and 5 to 7 mic. wide, 8 in each ascus. 
Collected at Cantwell Cave in Hocking County. On shaded sand¬ 
stone, intermingled with an ash-gray, crustose thallus, which appeared 
like a sterile Pertusaria. The type specimen is deposited in the writer’s 
herbarium, and a cotype may be seen in the State Herbarium. 
The plant resembles Buellia vernicoma Tuck. 
2. Rhizocarpon alboatrum (Hoffm,) Th. Fr. Nov. Act. Reg. Soc. Sci. 
Ups. HI. 3: 337. 1861. 
Lichen alboater Hoffm. Lich. Icon. 30. 1784. 
Thallus ash-gray varying toward white, commonly spread widely over 
the substratum as a continuous or rarely scattered or disappearing, smooth, 
chinky, verrucose-areolate, or sometimes mealy crust: apothecia small to 
middle-sized, 0.35. to 1 mm. in diameter, adnate or immersed, dull black 
and often more or less white-pruinose, flat with the black exciple visible, 
or convex when the exciple often becomes covered; hypothecium brown 
to black-brown; hymenium pale or tinged brown; paraphyses distinct, but 
sometimes coherent; asci clavate; spores oblong-ellipsoid, brown, 4-celled 
to muriform, 12 to 22 mic. long and 4 to 9 mic. wide (Fig.8j, 8 in each 
ascus. 
Collected in Butler, Preble, Ross, and Highland counties. On bark, 
especially elm bark. Also reported from Ottawa County. Rare but doubt¬ 
less distributed widely in the State. 
3. Rhizocarpon petraeum (Wulf.) Koerb. Syst. Lich. 260. 1855, 
Lichen petraeus Wulf. in Jacq. Coll. Bot. 3: 4. pi. 6. f. 2a. 1789. 
Thallus an ash or green-gray crust, or varying toward brown or brown- 
black, smooth to more commonly roughened, chinky to areolate, continuous 
or scattered, of moderate thickness, often widely and irregularly disposed 
on the substratum; apothecia small to large, 0.5 to 1.3 mm. in diameter, 
immersed to adnate, black-brown to black, flat with the concolorous 
