214 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
irregular, then usually spread over larger areas, usually dark orange in color, an upper 
cortex of thin-walled cells present; apothecia small or minute, 0.2 to 0.7 mm. in diam- 
eter, adnate, often more or less angular, commonly numerous and obscuring the larger 
portion of the thallus, the disk orange and usually flat, the thalloid exciple com- 
monly somewhat lighter-colored, entire; hypothecium commonly pale; hymenium 
pale below and yellowish or brownish above; paraphyses simple or rarely branched, 
slightly enlarged and colored toward the apex; asci clavate; spores ellipsoid, polar 
2-celled, 7 to 12 » long and 5 to 7 » wide. 
The plant is generally distributed over the State. On rocks. 
Common throughout the United States. Occurring also in all of the grand divisions, 
4. Placodium microphyllinum Tuck. Syn. N. A. Lich. 1: 174. 1882. 
Thallus composed of small and closely adnate squamules 0.5 to 1.5 mm. in diameter, 
these sometimes closely clustered toward the center into an areolate crust, dirt y green- 
ish-yellow and becoming dirty orange; marginal squamules often crenately lobed, 
often more or less obscured by minute yellow granules; a poorly developed upper cor- 
tex of thin-walled cells usually to be made out; apothecia small or minute, 0.3 to 0.5 
mm. in diameter, adnate, the disk flat and dark orange, the thalloid exciple usually 
crenulate and inclosing an entire proper one; hypothecium pale; hymenium pale 
below and yellow brownish above; paraphyses simple or branched, commonly, more 
or less enlarged and colored toward the apex; asci clavate; spores ellipsoid, polar 
2-celled, 9 to 15 » long and 5 to 7 » wide. 
Collected at Minneapolis. On old wood. 
Generally distributed over the northern United States, and once found as far south 
as Texas. A North American plant, but by no means common in its territory. 
5. Placodium citrinum (Hoffm.) Leight. Lich. Fl. Great Brit. 177. 1871. 
Verrucaria citrina Hoffm. Deutsch. Fl. 2: 198. 1795. 
Thallus crustose, composed of minute granules which are more or less scattered over 
the substratum or compacted into a subareolate crust, irregularly and often widely 
spread over the substratum, commonly lemon-colored; apothecia scarcely as large 
even as those of the last, adnate, the disk waxy-yellow or orange, commonly flat, the 
thalloid margin subgranulose, sometimes tending to disappear, said rarely to inclose 
a thin proper one; hypothecium pale; hymenium pale below and more or less yellow- 
ish brown above; paraphyses simple or branched, commonly somewhat enlarged and 
yellowish toward the apex; asci clavate to broadly clavate; spores ellipsoid or ovoid- 
ellipsoid, polar 2-celled, 8 to 14 » long and 4.5 to 7»: wide. 
Generally distributed over the State. On rocks. 
Widely distributed in the United States, but not yet known from the extreme South 
or West. Known in all of the grand divisions except Australia. 
6. Placodium aurantiacum (Lightf.) Hepp, Spor. Flecht, Eur. pl. 45. f. 899, 1857. 
Lichen aurantiacus Lightf. Fl. Scot. 2: 810. 1777. 
Thallus crustose, smoothish and chinky or more commonly becoming verrucose and 
rugose or even areolate, lemon-colored, pale or darker yellow, yellowish gray, gray, 
or finally whitish, rarely more or less dissected with black lines, somewhat corticate 
above, more or less irregular and often widely spread over the substratum; apothecia 
small or becoming larger, 0.4 to 1 mm. in diameter, sessile, the disk commonly flat, 
orange to saffron-colored, the thalloid margin paler and usually becoming crenulate, 
rarely disappearing and leaving only a thin proper exciple (biatoroid ); hypothecium 
pale; hymenium of same color below and yellowish or brownish above; paraphyses 
simple or quite frequently branched, usually somewhat enlarged and colored toward 
the apex; asciclavate; spores ellipsoid, polar 2-celled, 11 to 18 ¢ long and 6 to 9 wide, 
Generally distributed over the State. On trees, old wood, and rocks, 
Occurs throughout North America. Known in all of the grand divisions. 
