LICHENS OF THE STATE OF WASHINGTON 17 



6. ARTHONIACEAE 



Thallus crustose, thin, often beneath the substratum or lacking entirely, 

 no differentiation into layers. Apothecia circular to linear, sometimes 

 branched, single or clustered, in a stroma; proper margin absent or very 

 poorly developed, thalline margin absent; asci 1-8-spored; spores hyaline 

 or brown, 1 -many-septate or muriform. 



Alga Palmella, Trentepohlia, or Phyllactidium. 



8. Arthonia Ach. Neu. Jour, fur Bot. 1 : Part 3. 3. 1806. 



Thallus crustose to rarely areolate, or wanting, thin to rather thick, 

 sometimes developed within the substratum. Apothecia circular, elliptical, 

 or star-shaped, immersed to adnate; both margins absent; hypothecium 

 usually brownish ; paraphyses much branched ; asci usually 8-spored, some- 

 times 4-6, 6-8, or rarely 1-2, pyriform ; spores hyaline or rarely brown, 

 1 -many-septate, the cells often of unequal size. 



Alga Trentepohlia. 



A. Thallus crustose 



B. Disk white pruinose 4. A. impolita 



B, Disk not white pruinose, usually black. 



C. Apothecia irregular in shape, often branched. 



D. Spores 3-septate 5. A, radiata 



D. Spores 5-septate 2. A. excedens 



C. Apothecia elongated, not branched 1. A. complanaia 



A. Thallus squamulose. 3. A. glehosa 



1. Arthonia complanata Fee, Essai Crypt. Ecorc. OfiEicin. 54. 1824. 



Thallus grayish white or grayish green, superficial, thin, smooth to 

 rough and cracked. Apothecia 0.2-0.6 mm. wide, 1.3 mm. long, immersed to 

 adnate ; disk black, flat to convex ; asci 8-spored ; spores hyaline to brown- 

 ish, ovoid or ovoid-ellipsoid with one or both end cells enlarged, 4-6-septate, 

 21.0-32.0 X 6.0-10.0 ^. 



On bark: Grays Harbor Co.: Westport, 1908, Foster 670 (F), San 

 Juan Co. : San Juan Island, Friday Harbor, Fink (1935). 



2. Arthonia excedens Nyl., Act. Soc. Sci. Fenn. 7:484. 1863. 



Thallus grayish white to gray, superficial, thin to very thin. Apothecia 

 dark 0.5-0.8 mm. wide, 2.0 mm. long, circular to slightly irregular some- 

 what branched, partly immersed to adnate; disk black, rarely dark brown, 

 when moist, reddish, flat to convex ; asci 4-6-spored ; spores hyaline or 

 tinged with brown, ovoid-ellipsoid, 5-septate, 26.4-34.9 x 7.3-11.4 jn. 



On bark: Pacific Co.: Loomis Lake, 1931, 735, 1934, 2442; Chinook, 

 1940, 2807. Wahkiakum Co. : Cathlamet, 1940, 2918. Grays Harbor Co. : 

 Westport, 1908, Foster 718 (F). Thurston Co. : Gate, 1912, Foster (F). 



3. Arthonia glehosa Tuck. Gen. Lich. 221, 1872. 



