Tiny cladonia lichens growing on an ancient wooden picnic table in Troy. Photo by Dana Wilde

Henry David Thoreau, as we all know, spent a lot of time poking around in woods and fields. He spent hours pretty much every day observing nature in its smallest details. Then he’d go home and write up the day’s findings in his journals, which amount to thousands of pages and which many scholars say are his masterpiece.

Many of his writings, like “Walden” and a book unpublished in his lifetime titled “Wild Fruits,” a natural history of the plant life around Concord, Massachusetts, are made at least partly from his journals. So reading the journals, even in unedited form (the scholars have been working on them for more than 40 years and are still nowhere near finished), is sort of like walking the woods with Thoreau himself. His meticulous observations and ruminations are fascinating.

So I was poking around in these journals during some gray days awhile back when I noticed a strange phrase repeated in a number of places. “It is a lichen day,” he writes on Feb. 5, 1853. The same sentence again on Jan. 7, 1855; weeks later, on Jan. 22 and Feb. 16, “It is a good lichen day.” And on Dec. 6, 1859, “It is somewhat of a lichen day.” Obviously he’s looking at lichens. But what is “a lichen day”?

A shield lichen in Troy. Photo by Dana Wilde

Lichens aren’t really like any other being in the woods. They’re a symbiotic combination of two separate organisms, a fungus and an alga – which are as different from each other as both are from plants — growing together as one being. They come in three basic forms: foliose, which includes leaf-like structures with two distinct sides; fruticose, which includes hairlike and mushroomlike structures; and crustose, forming crusts over a surface. They grow on trees, stone, soil, houses, old picnic tables and other substrate surfaces. They absorb water and nutrients directly from the air and substrate. They go dormant in conditions of insufficient moisture, and turn back on to photosynthesize when conditions are right again. Some individual lichens are estimated to be thousands of years old. They tend to turn gray when dry, and gain color when in moisture. This is the clue.

Thoreau’s lichen days are usually damp, often in the middle of a winter thaw. “There is a low mist in the woods,” he writes Dec. 31, 1851. “It is a good day to study lichens.” Years later on Feb. 7, 1859: “I see the sulphur lichens on the rails brightening with the moisture. … A little moisture, a fog, or rain, or melted snow makes (a lichenist’s) wilderness to blossom like the rose.” A good lichen day is a moist day, when the lichens are actively photosynthesizing and their colors and textures are on full display, edifying the eyes, “A lichenist fats where others starve. His provender never fails.”

The spirit is fed by beauty found even in the most unlikely, rudest-seeming form on “the barest rocks.” (In fact, in March 1854 he tells us he literally “boiled a handful of rock-tripe (Umbilicaria Muhlen-bergii) … for more than an hour. It produced a black pulp, looking somewhat like boiled tea leaves, and was insipid like rice or starch.” Like his tries at eating a woodchuck and drinking tea made from arbor vitae, so much for that experiment.)

The scholar Hans Bergmann noted in a talk awhile back that “Thoreau did not know, as no lichenologist of his time knew, anything about the dual nature of the lichen. … The lichen is itself a miniature ecosystem.”

If he’d lived a few more years to find out the biological truth about lichens, Thoreau would no doubt have found it a profoundly illuminating natural fact. He was among the original naturalists to think of the whole Earth, not just his own woods, as one ecologically integrated process of processes. The whole Earth, he might have said, is a lichen, every part of it growing together as one being.

“The earth I tread on is not a dead inert mass,” he goes on to say Dec. 31. “It is a body – has a spirit – is organic – and fluid to the influence of its spirit—and to whatever particle of that spirit that is in me.”

Those lichen words lit up my gray February days 170 years later. It is a world of words to the end of it, to paraphrase another poet. A whole lichenlike ecology of words.

Dana Wilde lives in Troy. You can contact him at naturalist1@dwildepress.net. His book “A Backyard Book of Spiders in Maine” is available from North Country Press. Backyard Naturalist appears the second and fourth Thursdays each month.