Microcalicium arenarium (A. Massal.) Tibell
Non-lichenized lichenicolous Ascomycota Mycelium embedded in the host thallus (immersed), hardly visible as an indistinct whitish stain. Apothecia comprised of a cup-shaped head (capitulum) 0.2-0.3 mm diam., dull black tinged greenish or grayish, on a slender cylindrical unbranched stipe 0.5-2.5 mm tall, smooth or granular, concolourous to capitulum. Ascii 8-spored, urn-shaped, walls easily distorted. The capitulum contains a convex mass of loose, powdery greenish-black spores (mazaedium), usually with faint yellow pruina that tint the mazaedium greenish. Ascospores 1-septate (visible only when young), spirally ridged and striate when mature, 6-8 (10) x 2-2,5 µm according to literature, 5-9 x 2-3,5 µm according to our measures. No algal photobiont. Chemical spot tests negative or apothecia K+ yellowish brown. It parasitizes algae and lichens, in contrast to some other non-lichenized calicioids that are wood decayers. Mainly parasite of Psilolechia lucida or of free algae belonging to the Stichococcus genus or thalli of different Caliciales. Forming small colonies on these different hosts in microhabitats such as bark, wood, root of old oaks, and rock faces that are sheltered from precipitation. N.B. Specimen presented here are parasites of Psilolechia lucida (Photobiont: Stichococcus partly free-living and visible as green spots). Not to be confused with Calicium adspersum with larger spores and with a different capitulum and with Microcalicium disseminatum that grows on different caliciales with larger spores.
