82 PARMELIACEAE 



X. Medulla traversed by varying solid strands 



Letharia 218 

 y. Medulla uniform vifithout strands 



(x) Cortex formed of hyphae running lengthwise 

 m. Spores clear; asci 8-spored 



Bryopogon 219 

 n. Spores brownish ; asci 4-spored 



Alectoria 219 

 (y) Cortex of hyphae more or less perpendicular to the long axis, 

 pseudoparenchymatic 

 m. Medulla of hyphae running lengthwise 



(m) Medulla loose, not horny; apothecia unknown 



Thamnolia 225 

 (n) Medulla firm, horny 

 r. Thallus low, podetium-like ; apothecia unknown 



Siphula 225 

 s. Thallus fruticose, elongate; apothecia known 



(r) Thallus dorsiventral, without fibrous branches; medulla 

 and cortex not separable 



Everniopsis 218 

 (s) Thallus radial, usually with fibrous branches; medulla 

 and cortex readily separable 



Usnea 223 

 n. Medulla of hyphae running in all directions 

 (m) Thallus more or less hollow 

 r. Thallus swollen, tubular 



Dactylina 218 

 s. Thallus not swollen and tubular 

 (r) Thallus fruticose, erect 



Dufourea 218 

 (s) Thallus podetium-like; apothecia unknown 

 Endocena 226 

 (n) Thallus flattened, not hollow, dorsiventral 



Evernia 217 



(b) Spores 2-celled Ramalina 220 



(c) Spores muriform, brown, large; asci i-spored 



Oropogon 220 

 2. Algae bluegreen, Scytonema or Nostoc 

 a. Thallus large-leaved, with cyphellae, pseudocyphellae or cephalodia 

 (i) Lower side of thallus with cyphellae or pseudocyphellae 



(a) Apothecia with thalline exciple 



X. Spores clear, bacillar to acicular, 2-8-celled 



♦Podostictina 189 



y. Spores brown 



(x) Spores 2-celled Stictina 189 



(y) Spores 4-celled *Merostictina 189 



(b) Apothecia with proper exciple only 



*Dystictina igo 



