Verrucaria hydrophila

Verrucaria hydrophila is a crustose lichen that forms a thin thallus (main body) measuring 25–60 μm in thickness. The thallus appears smooth and is either continuous or has sparse cracks. Its colour ranges from grey-green to mid-brown, and when fresh and wet, it becomes somewhat translucent. Internally, the cells are arranged irregularly, showing at most a very weak vertical pattern. These cells are tightly packed together without air spaces between them. When present, the pigment in the cortical (outer) layer is brown. Characteristically, when multiple thalli of this species grow adjacent to each other, they are never separated by dark lines. The reproductive structures, called perithecia, form conical-hemispherical mounds that measure 240–400 μm in width. Initially, these are completely covered by a layer of thallus all the way to their apex (top). As they mature, the black apex of the involucrellum (protective covering around the perithecium) may become exposed. In a 25 mm2 area, one typically finds between 29 and 64 perithecia, with an average of 42. The ostiolar area (opening through which spores are released) is inconspicuous, either flat or convex, appearing as a pale dot measuring 15–50 μm in width. The involucrellum is conical in shape and extends to the substrate. …