KEY TO ORDERS AND FAMILIES 27 



LECANORALES 



A. Host usually a species of Myxophyceae 



B. Thallus taking its form from that of the algal host 

 C. Thallus appearing to be squamulose to foliose, 



algal host Nostoc 28. Collemaceae 



C. Thallus appearing to be crustose or more commonly dwarf- 

 like fruticose, algal host Scytonema or Stigenoma . ... 25. Ephebaceae 

 B. Thallus rarely taking its form from that of the algal host 

 C. Thallus large, plainly foliose 



D. Apothecia without exciple, sometimes borne on the 



under surface of the thallus 32. Peltigeraceae 



D. Apothecia with exciple, sessile; thallus commonly with 



cyphellae below 31. Stictaceae 



C. Thallus small, crustose to somewhat foliose or dwarflike 

 fruticose 



D. Thallus crustose to scaly or more or less fruticose 

 E. Thallus rarely differentiated into layers 



F. Algal host usually Gloeocapsa or Xanthocapsa 26. Pyrenopsidaceae 



F. Algal host usually Rivularia 27. Lichinaceae 



E. Thallus differentiated into more or less definite layers 29. Heppiaceae 

 D. Thallus somewhat foliose, commonly forming an irregu- 

 lar granulose crust 30. Pannariaceae 



A. Host a species of Chlorophyceae 



B. Apothecia without exciple or with rudimentary one, more 

 or less immersed in the thallus 



C. Thallus foliose, rather large; apothecia commonly large . 32. Peltigeraceae 

 C. Thallus crustose ; apothecia small 



D. Spores non-septate to several-septate 19. Lecanactidaceae 



D. Spores commonly transversely and longitudinally 



septate 22. Ectolechiaceae 



B. Apothecia with well-developed exciple 



C. Apothecia with both thalloid and proper exciples, the 

 thalloid one sometimes disappearing 



D. Apothecia more or less deeply immersed in the sub- 

 stratum 20. Thelotremaceae 



D. Apothecia somewhat immersed to more commonly 

 superficial 



E. Proper exciple dark 21. Diploschistaceae 



E. Proper exciple hyaline 23. Gyalectaceae 



C. Apothecia with either proper or thalloid exciple, but very 

 rarely with both 

 D. Apothecia with proper exciple 



E. Thallus taking its form from that of the algal host 24. Coenogoniaceae 

 E. Thallus not taking its form from that of the algal 

 host 

 F. Thallus foliose or 2-fold 



G. Thallus plainly foliose 35. Gyrophoraceae 



G. Thallus 2-fold 34. Cladoniaceae 



F. Thallus crustose to squamulose 



G. Spores brown 43. Buelliaceae 



G. Spores hyaline 



H. Apothecia usually yellowish ; spores non- 

 septate or septate with lenticular cells . 41. Caloplacaceae 

 H. Apothecia rarely yellowish ; spores non- 

 septate to septate with rectangular or 



cubical cells 33. Lecideaceae 



D. Apothecia with thalloid exciple 

 E. Thallus foliose or fruticose 



F. Thallus plainly foliose or rarely somewhat fruticose 

 G. Thallus small to middle-sized, foliose to 

 somewhat fruticose 

 H. Thallus more or less yellow in color; 



spores hyaline 42. Teloschistaceae 



