Calo0placa citrina. This is the species in the strict sense. The thallus is entirely granular sorediate with small spherical objects making up a frequently continuous thallus, the areolae are often completely covered. This species can often be completely infertile, when it occurs as a relatively coarse dust. The margins of the apothecia are usually covered with fine, sorediate material. It is a very common species indeed of most calcareous substrates and especially thos that are artificial. This photograph was taken on the walls of a sunken footpath leading from St Catherine's Wood, Jersey.