Acarosporaceae

← Back to Acarosporaceae in Family Index

Acarosporaceae is a family of primarily crustose, saxicolous (rock-dwelling) lichens, best known for their durability and ability to persist in dry, exposed, and climatically extreme habitats. Members of this family are common on bare rock surfaces where few other lichens can establish, often acting as early colonizers.

Growth Form and Thallus

The thallus is usually crustose and tightly attached to the substrate, making removal difficult without damaging the rock surface. It is commonly areolate or rimose, breaking into polygonal patches as it expands. Colors range from gray and brown to rust, black, or yellow-green, with some species showing bright yellow tones due to secondary metabolites.

Substrate and Habitat

Acarosporaceae species occur primarily on siliceous or calcareous rock, including cliffs, boulders, and exposed bedrock. They favor open, sun-exposed sites and are especially frequent in arid, alpine, or continental climates, though they are widespread in temperate regions as well.

Photobiont

The photobiont is a green alga, most commonly from the genus Trebouxia.

Reproductive Structures

Sexual reproduction is common and often conspicuous.

• Apothecia: Typically lecideine (black and lacking a thalline margin), often sunken into the thallus or individual areoles. Apothecia may be numerous and densely packed.
• Asci: Characteristically polysporous, containing many spores per ascus — a defining feature of the family.
• Ascospores: Small, simple, colorless, and ellipsoid.

Asexual reproductive structures such as soredia or isidia are uncommon in most genera.

Chemistry

Secondary chemistry is variable but often limited. Some species, particularly yellow forms, contain pulvinic acid derivatives. Standard lichen spot tests are frequently weak or negative, depending on the species.

Ecology and Role

Members of Acarosporaceae are highly stress-tolerant, surviving prolonged drought, intense solar radiation, and extreme temperature fluctuations. They play an important ecological role as pioneer species, contributing to rock weathering and early soil formation.

Representative Genera

• Acarospora – the largest and most widespread genus; typically areolate crusts with sunken black apothecia
• Sarcogyne – often dark to black crusts with prominent, crowded apothecia
• Pleopsidium – bright yellow crusts, frequently found in alpine or arid environments

Similar Crustose Families

Acarosporaceae may be confused with other rock-dwelling crustose lichen families, particularly in the field. Lecanoraceae also includes many saxicolous crusts but typically has lecanorine apothecia with a thalline margin and usually eight spores per ascus. Teloschistaceae often forms brightly colored yellow or orange crusts but differs chemically and commonly shows anthraquinone pigments and distinct spot test reactions. Rhizocarpaceae can appear similar in growth form but is characterized by muriform spores rather than the small, simple spores of Acarosporaceae.

Family overview intended for field study and photographic reference; microscopic examination is often required for confident identification.