The cyanolichens Erioderma pedicellatum and Coccocarpia palmicola need much more than a dewfall to fill their water holding capacity

Abstract Erioderma pedicellatum, an enigmatic boreal cyanolichen epiphyte is sympatric with the widespread pantropical cyanolichen Coccocarpia palmicola in cool and damp forests in Atlantic parts of Canada. After sampling co-occurring specimens of these lichens in Newfoundland, we quantified important hydration traits. We hypothesized that 1: these lichens restricted to wet forests have higher internal water holding capacity (WHCinternal) than what humid air and dewfall can provide, and 2: the rare E. pedicellatum has higher WHCinternal and / or WHCtotal than the widespread C. palmicola. Both hypotheses were supported: Mean WHCinternal across a wide thallus size range was 0.26 and 0.35 mm H2O in C. palmicola and E. pedicellatum, respectively; corresponding mean WHCtotal were 0.73 and 0.86 mm. These high WHC-levels could only be filled by liquid hydration sources. Because WHC strongly increased with thallus size, larger specimens needed even more water (1.7 mm), emphasizing these species’ dependency on rain and thus wet forests.