Hello I found this lichen on a Castanea tree branch. If somebody could point to the genus, and are these small powdery structures on the tips isidia? Many thanks! dion
Powdery is generally soredia: Isidia are often smooth or even shiny due to having a cortex. Isidia are usually more finger-like projections, but not always. I agree Hypogymnia. Getting this genus to species (in my region - am not familiar with the species range in Greece) usually also involves cutting open a tubular branch and noting what the interior ceiling and floor colours are (dark or white). Also I would note whether appressed, erect or drooping (sometimes good to see several sample or a large growth to assess that relative to other local species), if the branching is dichotomous or not, presence/absence of apothecia, side-buds, and location/structure of soralia. Hope that is helpful! cheers, frog
