| Upper surface of the thallus bearing cephalodia | 1. P. aphthosa |
| Upper surface of the thallus devoid of cephalodia. | |
| Thallus bearing trichomatic hyphae above. | |
| Upper surface bearing isidioid branchlets or lobules | 2. P. praetextata |
| Upper surface devoid of isidioid branchlets or lobules. | |
| Orbicular sorediate areas on the upper surface of the thallus | 3. P. sorediata |
| Soredia lacking on the upper surface. | |
| Lower surface of the thallus of light color | 4. P. canina |
| Lower surface partly or wholly dark | 5. P. rufescens |
| Thallus devoid of trichomatic hyphae. | |
| Apothecia orbicular and revolute, spores 4- to 8-celled | 6. P. polydactyla |
| Apothecia usually transversely oblong, spores 4-celled | 7. P. horizontalis |
1. Peltigera aphthosa (L.) Willd. Fl. Berol. Prodr. 347. 1787.
Lichen aphthosus L. Sp. Pl. 1148. 1753.
Thallus closely attached to the substratum at the center, the lobes ascending, 6 to 8 cm. in diameter, smooth and devoid of trichomatic hyphae above, cephalodia more or less rounded and irregularly scattered over the surface ([Fig. 3]), the lobes broad and rounded with crenate margins, brown above, the lower surface having numerous veins, these forming a dark brown nap at the center, the veins distinct and light toward the margin, dark rhizoids extending from the veins; medulla composed of thick-walled, densely interwoven hyphae, irregularly disposed; apothecia on extended lobules, orbicular and frequently revolute, the disk red-brown, 2 to 5 mm. in diameter, the margin entire or crenulate; hypothecium pale brown; hymenium hyaline to pale brown above; asci cylindrico-clavate; spores acicular, straight, 4- to 6-celled, 47 to 66 mic. long and 4 to 5 mic. wide ([Fig. 8], d).
Examined from Clark County. Also reported from Champaign County. On earth and often on humus-covered rocks. Rare in Ohio.
2. Peltigera praetextata (Sommerf.) Fink. Proc. Ind. Acad. Sci. 1918: 267. 1918.
Peltigera ulorrhiza praetextata Sommerf. Lapp. Suppl. 123. 1826.
Thallus adnate toward the center, more or less ascending toward the margins, 7 to 15 cm. in diameter, the upper surface having isidioid branchlets or lobules scattered more or less thickly, the lobes broad, wavy, crenate, with frequently isidioid, lobulate margins, trichomatic hyphae often present, usually green-gray toward the center, becoming brown toward the margin, the lower surface light with numerous dark veins and bearing rhizoids of the same color, the veins and rhizoids becoming light colored toward the margin; medulla of densely interwoven and irregularly disposed hyphae; apothecia on narrow, somewhat extended lobes, the disk brown to brown-black, revolute, 2 to 5 mm. in diameter, hypothecium light to darker brown; hymenium pale below and brown above; asci cylindrico-clavate; spores sub-fusiform to acicular, usually straight but sometimes slightly curved, 4- to 6-celled, 42 to 56 mic. long and 3 to 5 mic. wide.
Examined from Franklin, Adams, Butler, Marion, Jefferson, and Preble counties. On soil, old logs, and moss in woods. Not previously reported from Ohio, but included under Peltigera canina and Peltigera rufescens. Evidently widely distributed and frequent in the State, but seldom fruited.