Common Rim Lichen

not listed

NNR - Unranked

not listed

Lecanora pulicaris is a common rim lichen appropriately but unimaginatively named Common Rim Lichen. It occurs in Europe, western Asia, and North America. It is common in northeastern and north-central Minnesota, but it is absent from the remainder of the state.

Common Rim Lichen is extremely variable in both ecology and morphology. It grows on both the bark and the wood of trees. It prefers trees with acidic bark. In Minnesota, these include pine, spruce, and tamarack. However, it frequently grows on trees with slightly acidic bark, including birch, hawthorn, oak, alder, basswood, and ash. It sometimes grows on trees with more neutral bark, including elm and willow, especially in areas that have been affected by acid rain. It has also been collected on serpentinite rock.

The vegetative body (thallus) is crust-like (crusticose). It is usually thin, smooth, opaque, and continuous. It does not have a tough outer layer (ecorticate), it is not covered with a thin powdery substance (epruinose), and it does not develop asexual reproductive granules as it ages (esorediate). It is sometimes thicker, rough, and divided into islands separated by cracks (areolate). The areoles may be thick or thin, and they may be flat or be covered with wart-like elevations. The elevations may be moderate-sized (verrucose) or small (verruculose). The color may be yellowish white to yellowish gray or whitish gray to gray. The margin is indistinct.

Spore-bearing reproductive structures (apothecia) are common. They are disk-like and moderate sized, 1⁄64″ to 1⁄16″ (0.3 to 1.5 mm) in diameter. They may be stalkless or slightly constricted at the base causing them to appear almost stalked. The discs can be pale brown, reddish-brown, brown, dark brown, blackish brown, or black. The disc margins are persistent, and they are the same color as the thallus. They may be thin, relatively thick, or even prominent. They are smooth, not scalloped or wavy.

Trees

Crusticose

Bark

Pine, spruce, beech, and mountain ash

Sources

4, 26, 29, 30, 77, 81.

Common

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