76 BERNT LYNGE. M.-N. Kl. 



Physcia virella is a very variable plant. The soredia are frequently 

 yellow as in f. Hueana Harm. Catal. Lieh. Lorr. p. 235, but I have never 

 seen the »corpuscules plus ou moins écarlats« described by Harmand in 

 his form. — The soredia are at first small and well limited, later confluent. 

 Well grown specimens often show juvenile states of soredia, a frequently 

 occurring phenomenon with many characters of the Lichens. — The colour 

 of the thallus varies from pale greyish through pale brownish to dark 

 brown or even brownish-black. — Rhizinae are occasionally found on the 

 lower side of the apothecium. — Plants with a brownish colour and rhizi- 

 nose receptacle might probably as well be referred to PJi. obscura as a 

 var. sorediosa. But that involves an artificial and arbitrary limitation of 

 the species, for there are numerous intermediate states of colour and of 

 receptacles without rhizinae and receptacles with many rhizinae, although 

 the latter are rare. I prefer to use the soredia as a decisive character. 

 Physcia obscura without soredia, Ph. virella with soredia. The consequence 

 of this would be to propose a f. ciliata of Ph. virella as well as of Ph. 

 obscura, but it is not necessary, for I have not seen conspicuously crow- 

 ned apothecia in Norwegian Physcia virella. 



12. Physcia, lithotea (Ach.) Nyl. 



Parmelia cycloselis var. lithotea Acharius Methodus (1803) p. 199. 

 AcHARius Lieh. Univ. (1810) p. 483. 



Physcia obscura a orbicularis f. lithotea Th. Fries Lieh. Scand. I 

 (1871) p. 143. 



Physcia obscura f. lithotea Wainio Adjumenta I (1881) p. 133. Lynge 

 Blad- og busklaver. Berg. Mus. Aarb. 1910, no. 9, p. loi. 



Physcia lithotea Nylander De gonidiis etc. Flora 1877 p. 354. Crom- 

 BiE Brit. Lieh. I (1894) p. 318. Dalla Torre et Sarntheim Die Flechten 

 von Tirol (1902) p. 167. Olivier Lichens d'Europe I (1907) p. 244 (168). 

 Harmand Lichens de France (1909) p. 647. 



Physcia lithotea was recognized as a proper species for the first time 

 by Nylander 1. c. Nylander's statement: »Physcia lithotea, quae species 

 separanda est a Physcia obscura, texturam thalli aliam habente« is almost 

 a nomen nudum. The first author to give a full description oî Ph. lithotea 

 as a proper species, was Crombie. 



Exsic. Axzi Lieh. Ital. sup. 128 (f. sciastra, approaching to ï.nuda, 

 s. n. PariJielia obscura var. sciastra (Ach )). Arnold Lieh, exsic. 826, 



