tree hehn home | mom & dad

Sidewalks Alive

by Erhardt R. Hehn

Have you ever walked on a city sidewalk and wondered about the origin of the black splotches on the surface. I have, and assumed they were the result of splattered tar from street and roof repairing projects. The occasional splotches of color I attributed to discarded bubble gum. These assumptions were undoubtedly correct but they did not account for the most fascinating source of possible sidewalk ornamentation.

In the fall of 1990, daughter Jani and I started a world tour from Salt Lake City by train to San Francisco. After being settled in a smaller mid-town hotel, we decided to walk to a bus stop for a ride to Chinatown and our evening dinner. On stepping out of the hotel onto the sidewalk, I immediately noticed the unusual abundance of varied colored sidewalk splotches. You can attract considerable attention by squatting low as though you are searching for a lost valuable or preparing to respond to the call. Curiosity is heightened if you begin picking around on the sidewalk with your pocket knife. Occasionally I do embarrass my traveling companion by my antics and in this setting she tried to disassociate herself from me by taking an intense interest in the nearest show window. But I was not to be disowned that easily because I was elated with what I believed I was seeing. "Do you know that the green, blue, orange, red and brown splotches are alive? They are colonies of lichens!" I declared to the world. "Doesn't anybody else know this? These specks of life on a heavily trodden concrete sidewalk are a marvel of creation!"

This tenacious organism is a fungus living in harmony with a type of algae and is called lichen. The algae can live without the lichen but the lichen cannot live without the algae, because the algae provides the food for the lichen. This fungus cannot carry on photosynthesis. It is related to other fungi, as diverse as breadmold and mushrooms. The body of a lichen is branched and is called a thallus. It reproduces by means of spores and the scattering of fragments of thallus.

A return to San Francisco in 1992 found the lichens to be doing well on the downtown sidewalks. A recent trip to Washington, D.C. found them flourishing in bright colors on capital sidewalks. In a retirement subdivision in southern Florida they were flourishing, but only a light gray color. Lichens are widely adapted but I'm not certain that I have identified them in Bozeman sidewalks. Albeit that they are dead, a good example of lichens is found on the outside feature wall of the American Bank, 1632 West Main Street.

I recommend that you add searching for life on the sidewalks on your list of things to do on your next trip. In the course of your search guard against rear-ending someone, meeting a shopper with an armload of packages head-on or walking out into an intersection against the lights.

1994 Erhardt R. Hehn

top of page hehn home
last modified: 03dec01
Valid HTML 4.0!