Parmeliaceae

Parmeliaceae is one of the largest and most diverse families of lichens, composed primarily of foliose species, with a smaller number of fruticose and crustose forms. Members of this family are among the most familiar macrolichens on tree bark and rock, especially in temperate and boreal regions, and include many ecologically important and easily recognized taxa.

Growth Form and Thallus

The thallus is typically foliose, forming flat to loosely attached lobes that are appressed to loosely adnate. Lobes may be narrow or broad, rounded or elongate, and often form rosettes or overlapping mats. Surface texture ranges from smooth to wrinkled or ridged, and colors commonly include gray, blue-gray, greenish-gray, yellow-green, or brownish tones.

The underside is usually distinctly different in color, often black or dark brown, and bears rhizines that anchor the thallus to the substrate.

Substrate and Habitat

Parmeliaceae species grow on tree bark, wood, and rock, with some species favoring one substrate strongly. They occur in a wide range of habitats, from moist forests to open, exposed woodlands and rocky outcrops, and are especially abundant in clean-air environments.

Photobiont

The photobiont is a green alga, most commonly Trebouxia.

Reproductive Structures

Reproductive features vary widely across the family.

Apothecia: Usually lecanorine, with a thalline margin and a brown to black disc; apothecia may be common, rare, or absent depending on species.
Asci: Typically contain eight spores per ascus.
Ascospores: Simple, colorless, ellipsoid to oblong.

Asexual reproduction is very common, with many species producing soredia, isidia, pustules, or lobules, which are often essential for field identification.

Chemistry

Secondary chemistry is highly diverse and taxonomically important in Parmeliaceae. Numerous lichen acids are present, and spot tests (K, C, KC, P, UV) are frequently strong and diagnostic. Chemical differences are often critical for distinguishing closely related species.

Ecology and Role

Members of Parmeliaceae are ecologically significant macrolichens, contributing to nutrient cycling, habitat structure, and food sources for invertebrates and wildlife. Many species are sensitive to air pollution and are widely used as bioindicators of air quality.

Representative Genera

Parmelia – classic foliose lichens with broad lobes and simple rhizines
Flavoparmelia – yellow-green foliose species, often on bark
Hypogymnia – hollow-lobed lichens, common on conifers
Punctelia – foliose species with white pseudocyphellae
Usnea – fruticose “beard lichens” with a central cord

Similar Lichen Families

Parmeliaceae may be confused with other foliose lichen families. Physciaceae often has smaller, thinner thalli and different chemistry, with spores that are typically septate. Cetrariaceae includes foliose to fruticose species but differs in growth form and reproductive traits. Lobariaceae contains larger, softer foliose lichens that favor moist, old-growth forests and often have different photobionts or internal structures.

Family overview intended for field study and photographic reference; chemical tests and microscopic examination are often necessary for confident identification.