Product Code Database
Paracollema is a small genus of lichen-forming fungi in the family Collemataceae. It comprises two species of , characterised by their small size, gelatinous nature when wet, and distinctive reproductive structures. The genus was proposed in 2013 and later validated in 2017. Paracollema lichens form small, leafy thalli up to 1 cm in diameter, with dark olive green to brownish colouration. They are distinguished from related genera by their very small ascus and . Both known species are primarily epiphytic and have a limited distribution in southern Europe and northern Africa, typically found in Mediterranean or semi-arid climates.
Paracollema is placed within the family Collemataceae, order Peltigerales, class Lecanoromycetes. It is distinguished from other genera in the Collemataceae by its very small ascus and . The genus corresponds to the Collema Italicum-group defined by Gunnar Degelius in 1974.
Phylogenetic studies have shown that Paracollema forms a distinct clade within the Collemataceae, separate from Collema and other related genera. This molecular evidence, combined with the distinctive morphological features, supported the recognition of Paracollema as a separate genus.
The 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 , which is a protective outer layer of tightly packed fungal cells. Some species may develop isidia, which are small, cylindrical outgrowths that serve for vegetative reproduction.
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 are flat to slightly convex and dark red in colour. The apothecia have a thin, entire (an extension of the thallus tissue) and a (an inner layer of fungal tissue) that is , composed of interwoven .
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. Paracollema lichens also produce pycnidia, which are small, flask-shaped structures that produce called conidia. These are often present on the thallus surface.
Paracollema italicum, the type species of the genus, was originally described from Italy, as its name suggests. It has since been reported from other Mediterranean countries, including Spain and Morocco. 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. 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.
|
|
