Calicium is a genus of leprose lichens. It is in the family Caliciaceae, and has 40 species.
The sexual reproduction structures are a mass of loose ascospores that are enclosed by a cup shaped exciple sitting on top of a tiny stalk, having the appearance of a dressmaker's pin (called a mazaedium), hence the common name pin lichen. They are also commonly called stubble lichens.
They have been used as indicator species for old growth redwood forests.
Taxonomy
The genus was circumscribed in 1794 by the mycologist Christiaan Hendrik Persoon. He included three species in his initial circumscription of the genus: C. viride, C. salicinum, and C. pallidum. The genus name, derived from the Latin calix or calicis ("cup") with the diminutive suffix -ium, refers to the shape of the ascocarps.
Description
The genus Calicium features crustose lichens, which can be verrucose to granular in texture, or immersed in the substrate, and display a range of colours from grey to green-grey, pale yellow, or dark green. Its photobiont, a symbiotic green alga, is of the trebouxioid type. The ascomata (fruiting bodies) are apothecial in nature, usually elevated on a long, distinct stalk with a spherical to lens-shaped head, though some may be directly attached (sessile). These stalks consist of thickened hyphae that are brown to greenish-black and irregularly interwoven. The cup-shaped excipulum, a supportive structure around the ascomata, is well developed and envelops the dry spore mass.
The asci (spore-bearing cells) are cylindrical to clavate (club-shaped) and develop individually from ascogenous hyphae with croziers, typically dissolving early in their lifespan. Ascospores within the genus contain a single septum and form a distinctive black, dry-spore mass known as a mazaedium. These spores have a thick, dark brown wall, often adorned with unique ornamentation. They are generally in the size range 7–19 by 4–8 μm.
