@article {2495, title = {Systematics of the Usnea fragilescens aggregate and its distribution in Scandinavia}, journal = {Nordic Journal of Botany}, volume = {7}, year = {1987}, pages = {479-495}, issn = {0107055X}, doi = {10.1111/njb.1987.7.issue-410.1111/j.1756-1051.1987.tb00969.x}, author = {Clerc, P.} } @inbook {2472, title = {Usnea}, booktitle = {Lichens of Great Britain and Ireland}, year = {2009}, publisher = {British Lichen Society}, organization = {British Lichen Society}, address = {London}, author = {James, P.W. and Clerc, P. and Purvis, O.W.} }