Physciaceae

Physciaceae is a diverse family of lichens composed mainly of small foliose and crustose species, with occasional fruticose forms. Members of this family are common on tree bark, wood, and rock, especially in open, well-lit habitats, and include many species frequently encountered in urban and suburban environments.

Growth Form and Thallus

The thallus is typically foliose, forming small, thin rosettes with narrow lobes, though many species are crustose or squamulose. Lobes are often appressed to adnate, sometimes with powdery or granular surfaces. Thallus colors range from gray and blue-gray to greenish-gray or brown, occasionally with darker margins.

The lower surface is usually pale to dark brown or black, often bearing simple rhizines or lacking rhizines entirely in some crustose forms.

Substrate and Habitat

Physciaceae species grow on tree bark, wood, and rock, with some species favoring nutrient-enriched substrates. They are especially common in open woodlands, forest edges, roadside trees, and urban areas, and tolerate moderate air pollution better than many macrolichen families.

Photobiont

The photobiont is a green alga, most commonly Trebouxia.

Reproductive Structures

Reproductive structures are often present and useful for identification.

Apothecia: Typically lecanorine or biatorine, with a thalline margin that may be reduced or absent; discs are usually dark brown to black.
Asci: Usually contain eight spores per ascus.
Ascospores: Characteristically brown and septate (often one-septate), a key feature separating Physciaceae from many similar foliose families.

Asexual reproduction is common, with many species producing soredia, isidia, or granular propagules.

Chemistry

Secondary chemistry in Physciaceae is variable but generally less complex than in Parmeliaceae. Spot test reactions are often weak or inconsistent, though some species show diagnostic responses. Chemistry is usually of secondary importance compared to morphology and spore characteristics.

Ecology and Role

Physciaceae includes many ecologically flexible species that tolerate disturbance, nutrient enrichment, and moderate pollution. They are important components of early successional lichen communities on bark and rock and often dominate urban lichen floras.

Representative Genera

Physcia – common foliose lichens with narrow lobes and white pruina on apothecia
Phaeophyscia – foliose species with darker thalli and brown spores
Physconia – foliose species with broader lobes and well-developed rhizines
Buellia – primarily crustose species, many saxicolous or corticolous

Similar Lichen Families

Physciaceae may be confused with other small foliose lichen families. Parmeliaceae species are typically larger, have more complex chemistry, and produce simple, colorless spores. Candelariaceae includes yellow species but differs in spore color and chemistry. Teloschistaceae shares tolerance for exposed habitats but is distinguished by bright anthraquinone pigments and different spore morphology.

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