On December 22, 2021

Lichen colors offer protection

By Rachel Sargent Mirus

As I stroll through the cemetery near my home on a snowy day, splashes of golden orange, bright as daylilies in July, pop from the gray stones. These patches are elegant sunburst lichens, which provide a vibrant example of just how colorful lichens can be. Lichens come in a wonderful range of colors, from the subtle pale green of old man’s beard to the brilliant yellow of goldspeck lichens. While these colors can be beautiful, they are also useful, as the pigments block harmful ultraviolet rays, allow lichens to absorb light as heat, and protect them from harmful microbes.


All lichens are a partnership of at least two microorganisms: a fungus and a photosynthesizer. Some of a lichen’s apparent color comes from the presence of pigments, or colored chemicals, within the protective skin. This skin is called a cortex and is created by the fungal partner along the lichen’s upper surface. Below this protective skin sits the photobiont: the photosynthesizing partner. If there is no special pigment in the cortex, lichens appear gray to grayish-green when dry.

When wet, however, lichens frequently change color dramatically, as the cortex becomes more transparent and the color of the photobiont shines through. Lichen photobionts can be different kinds and colors of algae or cyanobacteria, with their signature hues determined by their own set of photosynthesizing pigments, such as chlorophylls or carotenoids. Lichens with green algae partners often turn grass-green when wet. Cyanobacteria photobionts are blue-green to blue-gray, but lichens with cyanobacteria partners often appear black and jelly-like when wet.

Lichens living in exposed habitats are more likely to have deep colors and contain higher levels of pigment in their cortex than lichens living in shaded habitats, suggesting that their colors protect against sunlight. Lichen photobionts are vulnerable to excessive light, especially ultraviolet rays. The pigments found in the cortex of lichens can absorb or scatter ultraviolet wavelengths, shielding the photobiont like a sunscreen.

The most common brightly colored pigment found in the cortex of lichens is usnic acid, which gives lichens a pale yellowish-green hue. This is the classic color of beard lichens, those stringy clumps that hang from branches. Pale yellow usnic acid is best at blocking short wavelengths of ultraviolet light.

A category of pigments derived from pulvinic acid gives some lichens a brighter yellow color. The powdered sunshine lichen, which grows in frilly patches on both rock and wood, is a widespread northern example. The intensely yellow pulvinic acid pigments in their cortex block longer ultraviolet wavelengths.

Lichens that range from golden yellow to orange and bright red contain anthraquinone pigments. This is the pigment that gives the elegant sunburst lichen its summer-like hues even in the cold of winter. These pigments also give the British soldiers lichen its titular red tops.

Lichens containing melanin pigments will be shades of brown when dry. One example of melanin-containing lichen is rock tripe, whose large, brown flakes often grow on boulders and cliff sides. Melanin pigments act broadly, blocking a wider spectrum of light. Some lichen colors, particularly dusty white hues, come from physical structures on the lichen that scatter light, rather than from a chemical pigment. These structures can also protect against damaging levels of ultraviolet light.

Additional observations by lichenologists suggest that lichen colors may do even more than protect against sunlight. Lichens from northern regions with longer, colder winters tend to be darker than their hot-habitat counterparts, which may allow them to absorb light and keep that energy as warmth. Additionally, some lichen pigments, including usnic acid, have antimicrobial properties that can protect a lichen from attack by outside bacteria and fungi. Antimicrobial compounds likely give the slow-growing lichens a competitive edge in their harsh natural habitats.

While lichens are around all year, their small stature leaves them easily obscured by summer’s exuberant plant growth. It may be long months before the flowers in our gardens bloom. In the meantime, I’ll look for lichens’ bright colors shining through the snow.

Rachel Sargent Mirus lives in Duxbury, Vermont. Illustration by Adelaide Murphy Tyrol. The Outside Story is assigned and edited by Northern Woodlands magazine and sponsored by the Wellborn Ecology Fund of the New Hampshire Charitable Foundation: nhcf.org.

Do you want to submit feedback to the editor?

Send Us An Email!

Related Posts

Moving sticks and rocks

May 22, 2024
By Merisa Sherman Then the tough choice of how to play today:ski, bike, paddle, fish, hike, run?  The bug went down my throat. Literally, flew down my throat and landed in the back at such speed that I had no choice but to just swallow. Mmmmm, gotta love that extra protein that Vermont provides during…

What are the chances?

May 22, 2024
Vesna Vulovic is a name etched in the annals of miraculous survival — perhaps the most unlikely survival story of all time. She was thrust into the spotlight on Jan. 26, 1972, when she unwittingly became a symbol of human resilience.  A native of Belgrade, Yugoslavia, Vesna’s journey to that fateful day began like that…

The Outside Story: Jesup’s milk-vetch: A rare beauty

May 22, 2024
A few ledges along the Connecticut River are home to a rare plant commonly known as Jesup’s milk-vetch (Astragalus robbinsii var. jesupii). In fact, this species, which has been listed as federally endangered since 1987, only grows at six sites along a 16-mile stretch of the river in New Hampshire and Vermont. But conservationists are working…

Boys, brothers, dad, Vermont

May 22, 2024
Building a Killington Dream Lodge: part 14 By Marguerite Jill Dye Dad made progress and forged ahead on our Killington ski lodge while Mom, Billie, and I toured Europe. Our extensive European whirlwind trip was the very beginning of my awakening to understand the world and how I fit in. I had no idea what…