Lecanactis Minutissima

''Lecanactis'' is a genus of crustose lichens, commonly called old wood lichens. The mycobiont (fungus partner) 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 (fruiting bodies) 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 (''actis'') 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 (the K test) 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 (occasionally eight) internal wall (septa); the walls stay thin and do not bulge at the septa. Separate flask-shaped structures (pycnidia) 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 (Eastern Hills) 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

*'' Lecanactis abietina''
*'' Lecanactis borbonica''
*'' Lecanactis canariensis''
*'' Lecanactis citrina''
*'' Lecanactis coniochlora''
*'' Lecanactis latispora''
*'' Lecanactis leprarica'' – Cameroon
*'' Lecanactis luteola''
*'' Lecanactis malmideoides'' – South America
*'' Lecanactis minuta''
*'' Lecanactis minutissima''
*'' Lecanactis mollis''
*'' Lecanactis neozelandica''
*'' Lecanactis platygraphoides''
*'' Lecanactis proximans''
*'' Lecanactis quassiae''
*'' Lecanactis rubra'' – Madagascar
*'' Lecanactis spermatospora''
*'' Lecanactis subdilleniana''
*'' Lecanactis subfarinosa''
*'' Lecanactis submollis''
*'' Lecanactis sulphurea''

References

{{Taxonbar , from1=Q6511472 , from2=Q7399188

Roccellaceae
Arthoniomycetes genera
Lichen genera
Taxa described in 1855
Taxa named by Gustav Wilhelm Körber