Calicium chlorosporum

Calicium chlorosporum is a crustose lichen that is found growing on trees throughout much of the world.

Morphology
The lichen has a lichenized life habit. Its thallus is verrucose, areolate or subimmersed, and pale brownish yellow to beige in color.

The apothecia are 0.75-1.1 mm high and 6-9 times as high as the width of the stalk. The stalk is shining black or has a brownish pruina in the uppermost part, is rather thick at 0.8-0.16 mm in diameter, and consists of dark greenish brown, sclerotized, and irregularly interwoven, 2-3 μm thick hyphae. The outermost part of the stalk is pale brown and surrounded by a 2-4 μm thick, hyaline, I-, gelatinous coat.

The capitulum is broadly obconical to lenticular, black, and has a brownish or sometimes bright yellow pruina on the lower side, measuring 0.29-0.45 mm in diameter. The mazaedium has a faint yellow pruina, particularly in young ascomata. The exciple is densely interwoven and heavily sclerotized, and the hypothecium has a flat upper surface, is dark brown, and has reticulately interwoven hyphae.

The asci are cylindrical, with uniseriate or slightly overlapping spores that are 33-36 x 3.5-4.5 μm. The ascospores are ellipsoid, distinctly ornamented with spirally arranged ridges and a few irregular cracks, and measure 10.5-12.5 x 5-6 μm.

Chemistry
Spot tests show the thallus is K+ yellow turning red or K-, C-, P+ yellow, UV+ intensely yellow or dull (varying amounts of xanthones). The brown pruina is K+ violet-red, with feather-like crystals. All parts of the apothecia are I-.

The thallus contains the secondary metabolites placodiolic acid, +norstictic acid, and unidentified xanthones.

Ecology and distribution
Calicium chlorosporum grows on the bark of Jatropha at low, coastal elevations. Its known distribution includes Africa, North America, Central America, South America, and Australasia, with a record from Baja California in the Sonoran region.