Paracollema

Paracollema comprises small, leafy lichens known as jelly lichens due to their gelatinous nature when wet. These lichens form small thalli, reaching up to 1 cm in diameter, which are dark olive green to brownish in colour.^[2] The thallus is homoiomerous, meaning that the fungal hyphae and photobiont cells are evenly distributed throughout, without distinct layers.^[2]

The lobes of Paracollema lichens are small, entire, and rounded, typically measuring up to 3 mm in width. Their surface can be smooth or slightly wrinkled. Unlike some related genera, Paracollema lacks a cortex, which is a protective outer layer of tightly packed fungal cells.^[2] Some species may develop isidia, which are small, cylindrical outgrowths that serve for vegetative reproduction.^[3]

Apothecia (fruiting bodies) are often present and numerous in Paracollema species. These disc-shaped structures are sessile (attached directly to the thallus without a stalk) and appear on the upper surface of the lobes. The discs are flat to slightly convex and dark red in colour. The apothecia have a thin, entire thalline margin (an extension of the thallus tissue) and a proper exciple (an inner layer of fungal tissue) that is euthyplectenchymatous, composed of interwoven hyphae.^[2]

A distinctive feature of Paracollema is its remarkably small reproductive structures. The asci, sac-like structures that produce spores, are very small, measuring only 30–45 μm long and 8–9 μm wide. Each ascus typically contains eight spores. The spores themselves are also diminutive, ranging from 10 to 13 μm in length and 3–4.5 μm in width. They are narrowly ellipsoid or somewhat oblong in shape and have two cells separated by a single septum.^[2][3] Paracollema lichens also produce pycnidia, which are small, flask-shaped structures that produce asexual spores called conidia. These are often present on the thallus surface.^[2]

Paracollema comprises two known species, both of which have a relatively limited distribution in southern Europe and northern Africa.^[2] These lichens are primarily epiphytic, meaning they grow on the bark of trees.^[2]

Paracollema italicum, the type species of the genus, was originally described from Italy, as its name suggests.^[3] It has since been reported from other Mediterranean countries, including Spain and Morocco.^[2] This species tends to favour areas with a Mediterranean climate, characterised by warm, dry summers and mild, wet winters.

Paracollema almbornii has a similarly restricted distribution. It was first described from Morocco and has subsequently been found in other parts of North Africa and southern Spain.^[2] Like its congener, it is typically found in regions with a Mediterranean or semi-arid climate.

Both species show a preference for bark substrates, particularly those of deciduous trees. They are often found in open woodland habitats or on isolated trees in agricultural landscapes where they receive adequate light exposure. The restricted distribution of Paracollema species suggests they may have specific environmental requirements or limited dispersal capabilities.^[2]