Lecanactis


Lecanactis is a genus of crustose lichens, List of [common names of lichen genera|commonly called] old wood lichens. The mycobiont is in the family Roccellaceae. The photobiont is an algae in the genus Trentepohlia. These lichens typically grow as thin crusts on tree bark or rocks, producing small black fruiting bodies that may appear as round discs or elongated slits. The genus contains about 20 species found worldwide, with some species considered rare and threatened by habitat loss.

Taxonomy

The genus was circumscribed in 1855 by the German lichenologist Gustav Wilhelm Körber, who assigned Lecanactis abietina as the type species. In his original description, Körber characterised Lecanactis as having pseudolecideine apothecia that are initially closed, then become widely open, with a rounded to somewhat irregular form. He noted that the apothecia typically have a prominent margin and distinguished the genus by its spore-bearing structures and thallus characteristics.
Körber initially included several species in the genus, including L. abietina, L. dilleniana, and L. biformis. He recognised Lecanactis as a transitional genus that connects the lichens with the forms, noting the unique combination of initially closed apothecia that later expand and the distinctive thalline characteristics that separate it from related genera such as Opegrapha. The genus name Lecanactis reflects the -like appearance of the apothecia combined with their distinctive radiating or star-like arrangement when mature.

Description

Lecanactis species produce a thin, crust-forming thallus that adheres tightly to bark or rock. The surface may appear smooth, scurfy, cracked into irregular plates, or even minutely warted; a few species develop a powdery, texture. Some thalli spread without a clear edge, while others are neatly outlined by a dark brown to black marginal line called a. Unlike many lichens, the outer skin is either rudimentary or absent, leaving the internal fungal tissue exposed. The photosynthetic partner is always a filamentous green alga from the genus Trentepohlia, whose orange-tinged cells often tint the lichen faintly when viewed through a hand lens.
Reproduction takes place in small fruiting bodies called apothecia, which can be round or elongate, pencil-like slits that sit directly on the thallus surface. They are usually black but are often dusted with a pale, chalky bloom. Because the surrounding thallus tissue does not form a border, the apothecia are rimmed only by the fungal —a dark, usually raised wall that can also pick up a pruinose coating. In microscopic section the exciple and underlying tissue are deep brown, and their pigments turn green when a drop of potassium hydroxide solution is applied. Inside each apothecium the hymenium—the fertile layer—is either iodine-negative or briefly stains reddish to blue. Slender, sparsely branched paraphyses stand among the asci, each paraphysis swelling slightly at its tip.
Every ascus typically contains eight colourless, spindle-shaped ascospores that are divided by three to seven internal wall ; the walls stay thin and do not bulge at the septa. Separate flask-shaped structures erupt as conspicuous, white-dusty cylinders and release minute, rod-like conidia that provide an additional means of dispersal. Chemically the genus is marked by the presence of orcinol-type depsides and β-orcinol depsidones, along with erythrin and several lesser-known substances.

Conservation

Lecanactis proximans was assessed as critically endangered in 2023 for the IUCN Red List. The lichen is known from a single location in the Cerros Orientales of Bogotá, where it is threatened by habitat alteration and deforestation due to urban expansion, industrial development, and agricultural encroachment. The species has not been rediscovered in surveys of remnant forest patches in the area.

Species