The Carlisle Mosquito Online

Friday, November 12, 2004


Biodiversity Corner: Smoky-Eye Boulder Lichen

"Every hundred years I'll add an inch or two to my character.

A millennium later I'll still lack all presumption.

And still grasp the rock of my choice with a full-bodied embrace."

Extract from Lichen, in Northern Latitudes, by Lawrence Millman, who was featured in last Sunday's Boston Globe Magazine.

Smoky-eye boulder lichen as found on the Conant Land (inset) and a close-up of the lichen. (Photo by Kay Fairweather)

Name: Porpidia albocaerulescens or smoky-eye boulder lichen. There are 23 species of Porpidia in North America. They are referred to collectively as boulder lichens but while all Porpidiae grow on boulders, not all lichens on boulders are Porpidiae.

Word for the day: "Saxicolous" means growing on rock, stone, brick or concrete. Lichens in the genus Porpidia are saxicolous and most grow on rocks rich in silica and lacking calcium. The lichens growing on the marble monument at the rotary are also saxicolous but they clearly have an affinity for calcium.

When and where seen: Smoky-eye boulder lichen can be seen all year round. The sample in the photo is growing on a granite boulder in the Conant Land. The inset in the photo shows the vertical face of the boulder mostly covered with the lichen, bordered with moss on the left side, and an area in the top right where you can still see the granite surface. This lichen is quite common in the East on rocks in shaded woods. I have some in my back yard.

Distinguishing characteristics: The smoky-eye boulder lichen is a crustose lichen, meaning that it is very closely bonded to its substrate and forms a crust over it. The thallus, or lichen body, is a pale greenish-gray, fairly smooth, continuous coating on the rock. The surface may show fine cracks where the thallus is thickest. It is randomly dotted with fruiting bodies (called apothecia) which are circular and gray with a black margin. The apothecia have a powdery frosty-like deposit on them. Many lichens are difficult to identify but this one is quite distinctive. If you see those little smoky eyes with their black eye-liner looking at you from a smooth greenish-gray coating on a rock, you can say with some confidence, "Back at ya, Porpidia."

References: Lichens of North America, by Brodo, Sharnoff and Sharnoff.

Submissions for the Biodiversity Corner are encouraged from everyone. The column is now three years old (first publication on November 9, 2001) and we've barely scratched the surface of the town's biodiversity. You could still be the first to write up a moss or a fish. In a short field trip in the Conant Land with lichenologist Elizabeth Kneiper in March of this year, we identified about 50 species of lichens. Send your ideas, your nature photos, or the whole column to Kay Fairweather at 392 School Street, Carlisle MA 01741 or to

2004 The Carlisle Mosquito