Changes in thalli of L obaria species during 1986-1998 are assessed using fixed point quadrats on trees in sites across Britain in a range of atmospheric and management conditions. Growth patterns for British species of L obaria are described and factors contributing to their present status in Britain assessed. Results show that the pattern of growth, fragmentation and subsequent coalescing of fragments makes it difficult to estimate the age of a thallus. Little evidence of establishment from propagules was found over 10 years except in L. scrobiculata. The effects of loss of habitat and veteran trees, climate changes, of declining bark pH, and of competition with bryophytes are discussed.