222 HERRE 



It probably occurs beside all perennial streams in deep and shady 

 canons. Found in both North and South America. 



LVI. Usnea (Dill) Pers. 



Usnea Dillenius, Hist. Muse. 56. 1741, in part. 

 Usnea Persoon in Ust. Ann. Bot. 21. 1794. 



Thallus erect and shrub-Uke or excessively elongated and pendu- 

 lous, more or less thread-Hke, often forming intricately branching 

 and entangled mats, without rhizoids but attached by a holdfast; 

 structure radial, alike on all sides, naked, or usually beset with fibrils, 

 smooth or rough; cortex horny, of irregular or nearly perpendicular 

 hyphae; outer medulla cottony; inner medulla a solid, cartilaginous, 

 central cord of longitudinal, thick- walled hyphas; soredia often abun- 

 dant. 



Apothecia circular, usually large and conspicuous, lateral or ter- 

 minal, shield-like, with pale, often pruinose apothecia, usually 

 fringed with long fibrils; paraphyses branched, capitate, septate; 

 spores 8, small, colorless, ellipsoid to globose. 



A large genus, many of the species really but variable conditions 

 of polymorphic species; found all over the world, usually on bark, 

 rarely on rocks. 



KEY TO SPECIES. 



A . Plants small, erect, shrub-like. 

 B. Color gray-green. 



C. Without soredia i. florida 



CC. Soredia more or less abundant 2. hirta 



BB. Color rusty red 3. rubiginea 



AA. Plants more or less pendulous. 



D. Sub-erect or short pendulous 4. ceratina 



DD. Pendulous, tangled, long to very long. 

 E. Fibrils numerous. 



F. Thickly set with short spreading fibrils 5. dasypoga 



FF. Fibrils nearly straight, horizontal 8. longissima 



EE. Fibrils very few or wanting. 



G. Thallus broken into distinct joints 7. articulata 



GG. Thallus not articulate. 



H. Without spreading fibrils 6. plicata 



HH. Smooth or with very few fibrils .9. calif ornica 



