Smoky-Eye Boulder Lichen

Smoky-eye boulder lichen, Porpidia albocaerulescens, closeup showing apothecia
Scientific Name
Porpidia albocaerulescens
Lecideaceae (a lichen family)

Smoky-eye boulder lichen is a common crustose species that grows on rocks. Its thallus (main body) is pale gray or greenish gray (when wet, yellowish gray) and often covers an area 6 inches wide or more. Its button-shaped apothecia (spore-producing structures) are dark, bluish gray with black rims.

Like other crustose lichens, smoky-eye boulder lichen is tightly attached to the substrate they grow on. They look like a spritz of spray paint, and the surface may be cracked.

A lichen is an organism that results when a fungus species and an algae species join together. Although the relationship between the fungi and algae is quite intimate and integrated, the lichen that is formed does not much resemble either of the components. Learn more about lichens on their group page.

Similar species: Two other species in genus Porpidia are recorded for Missouri:

  • The concentric boulder lichen, or crust porpidia (Porpidia crustulata), also grows on rocks. Its pale, grayish thallus is often circular, and its outer margin often has lighter and darker concentric rings. The small apothecia are dark, blackish, and look like tiny warts or moles (they are convex). The apothecia are often organized in roughly concentric rings within the thallus.
  • Cracked pots (Porpidia tahawasiana; syn. P. subsimplex) is another boulder lichen. The common name refers to the cracked, bent or otherwise distorted rims of its apothecia disks, which have blackish rims and centers.

Missouri has roughly 200 species of lichens that have a crustose growth form. The smoky-eye boulder lichen is widespread and fairly easy to identify.

Other Common Names
Smokey-Eyed Boulder Lichen

Lichens begin as tiny spots but may grow to cover several square inches. The smoky-eye boulder lichen easily reaches 6 inches in diameter and frequently covers large portions of boulders.

Where To Find


This lichen species is saxicolous: it lives on rocks. It is especially common on sandstone rocks, in shaded places. (So you'll usually see it in the woods.) Often, you’ll see it competing with mosses on the same rock.

Lichens contribute to a beautiful landscape. And when you start seeing them, and really paying attention to their forms and colors, you may become enchanted with their strange beauty.

Because lichens, with their soft, absorbent tissues, are extremely sensitive to air pollution, they are good indicators of air quality. Scientists use them as sentinels of air quality and forest health.

Some lichens can live for a very long time — hundreds or even thousands of years. Because their growth rate is steady, they can be used to estimate dates in the past. It’s called lichenometry, and it’s similar to tree-ring dating. It works in rocky landscapes where trees are scarce. Many lichens begin as a dot on an overturned or newly exposed rock face and then grow outward, slowly, in a circular pattern. Measuring the diameter of the largest lichen on a rock face shows how long the rock has been exposed, at a minimum.

It’s interesting to observe how lichens, mosses, and liverworts compete with each other on the surface of their common substrate. It’s a lot like how marine creatures must fight for a toehold on a crowded coral reef. Sea stars, urchins, corals, anemones, scallops, mussels, tube worms, and more can only live when attached to the correct surface, and they cannot overlap.

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Similar Species
About Mosses, Liverworts, and Lichens in Missouri

Mosses, liverworts, hornworts, and lichens seem rather similar, but these organisms are in very different groups. Mosses, liverworts, and hornworts are small, low plants usually found in damp habitats. Unlike more familiar plants, they lack veinlike structures and do not produce flowers or seeds — instead, they produce spores. Meanwhile, lichens are not plants at all: they are a collection of different fungi that have photosynthetic algae living within their tissues.

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