Figure 1: Lichens on the Ceanothus in the Graham Visitors Center parking lot, including Ramalina farinacea, Usnea species (fruticose), Evernia prunastri and Physcia tenella (foliose).
TEXT BY KATHERINE GLEW | Photos by Richard Droker
Hidden beneath the leaves and flowers in the Washington Park Arboretum are cryptogams: lichens, mosses and mushrooms that reproduce via spores rather than seeds or flowers. Most folks are familiar with mosses and mushrooms, but how much do you know about the lichens?
Lichens are symbiotic organisms made up of a fungus (the mycobiont) and one or two photobionts—partners that can photosynthesize, such as green algae or cyanobacteria. Some lichens are made up of a fungus, green alga and a cyanobacterium in a single body or thallus. The two to three organisms live together, mutually benefiting from the relationship. The photobiont provides food for the fungi, capturing sunlight and converting carbon dioxide into sugars the fungi can use as food. In exchange, the fungus provides a safe haven or home for the photobiont to survive when the environment becomes too dry or too bright.
I have been leading lichen walks in the Arboretum for more than ten years. Lichens can be found on all surfaces here, including tree bark, branches, rocks, soil, leaves, cement, benches, and the wood rafters of the arbor at the Graham Visitors Center. They can even be found growing on old cars, like mine. At one of my lichen walks, a participant drove her car to the parking area to show it off to the class. It was covered in baby lichens!
Figure 2: Parmelia sulcata and Melanelia lichens (both foliose) on tree bark in the Visitors Center parking lot.
Classification, Color and Form
Though the two sometimes look similar, lichens are not related to mosses. Taxonomically, lichens are classified by their fungal component and belong to the kingdom Fungi, whereas mosses are true plants in the plant kingdom, Plantae. Green algae (also members of Plantae) carry out the photosynthesis for the majority of lichens, while cyanobacteria (in the Domain Bacteria) photosynthesize for about 10 percent of them.
Lichens come in many colors and forms. Colors include—but are not limited to—grey-green, brown, blue-green, yellow, orange, and grey. Though infrequent, lichens can also be emerald green, like most of the mosses. Three lichen growth forms are most commonly observed: 1) foliose—leafy, with an upper surface that’s different in color from the under-side; 2) fruticose—hairy or shrubby, with the same color all around; and 3) crustose—crusty, and hard to remove from a tree or rock.
Components of the Food Web
Lichens are an important part of the food web. Many animals eat them, including mammals, birds and insects. Deer eat Usnea and Bryoria lichens. In the winter, lichens provide food for deer, reindeer and other mammals. In Tundra areas, caribou and reindeer are known to fight over lichen patches for winter food.
In addition to contributing to the food web in ecosystems, lichens can also provide shelter, nesting material, and homes for wildlife and invertebrates. Our local hummingbirds and bush tits use the wax-paper lichens and other species for nesting material. Flying squirrels add lichens to their winter nests and munch on them over the winter. Insects and mites call them home. Some insects have evolved to mimic lichens as camouflage, blending with branches and rocks.
Figure 3: Lichens growing on the arbor rafters to the south of the Graham Visitors Center, including Ramalina farinacea (fruticose), Evernia prunastri (foliose), and large patches of dust lichen (crustose).
Lichens add to the biological diversity of our world, which is important for the survival of all life. Between 1500 and 2000 described lichen species are found in Washington state. North America claims nearly 6100 of described lichen species. Worldwide, more than twenty thousand lichen species have been described, and some experts estimate that another thirty thousand more species have yet to be discovered!
Facilitating Plant Life
As pioneer species, lichens—along with mosses—colonize habitats early after disturbances such as fires, floods, volcanic lava flows, and glacial recession. They grow on soil and rock, breaking down the substrate into a usable form for seeds of plants to germinate. Essentially, lichens and mosses can condition the debris and rocks to make it habitable for plants. Some lichens in the boreal and arctic north are essential for the germination of some tree species.
Cyanolichens, those that contain cyanobacteria, are what we refer to as “nitrogen fixers.” This means they absorb nitrogen gas from the air, converting it into a chemical form that can be taken up by plant roots to boost their growth and development. Furthermore, when these lichens die and fall to the ground, they decompose and add more nitrogen to the soil. The number of cyanolichens in urban areas is lower compared to non-urban areas. Cyanobacteria are sensitive to air pollution, such as nitrous oxides, sulfur dioxide, lead, ozone, carbon monoxide and particulate matter.
Both green algal and cyanobacterial partners can contribute other nutrients to ecosystems and help with water cycling. Like mosses, lichens can intercept and hold moisture, capturing it from dew, rain, and the atmosphere during foggy periods. Later, when they fall to the ground, they release the moisture into the soil as they decompose on the forest floor and in gardens. If not for the lichens and mosses, these nutrient and moisture resources could be lost or unavailable to plants. In this way, lichens can influence both the humidity and temperature within the forest canopy, as well as in our city parks and gardens.
Lichens and mosses also form part of what scientists refer to as microbiotic or cryptogamic crusts, which help bind soil into stable aggregates, reducing erosion. They form a network that acts like a “skin” on top of the soil, holding it together. In deserts and range areas, lichens, fungi, moss and cyanobacteria intercept water run-off, preventing water loss on the soil. Overgrazing by cattle, cows and sheep can break down these microbiotic crusts, resulting in erosion and allowing the soil to blow free. (Overgrazing was one of the main causes of the “Dust Bowl” in the 1930s.)
Figure 4: Cladonia chlorophaea (fruticose with a scaly base) on liverwort and moss on a tree stump on the west side of the Visitors Center.
Indicator Species and Human Uses
Recently, lichens have been monitored by the United States Forest Service and Bureau of Land Management as indicators of air pollution, environmental conditions, and climate change. If the air is too polluted, many lichen species will disappear from an ecosystem. These agencies monitor the presence and absence of lichens, as well as specific lichen species, to determine forest and urban health.
Lichens have also been collected for many human uses over the centuries. The French found lichen oils to be useful in retaining the floral fragrances used in perfumes. The Scots used lichens to make dye and create a variety of purples and reds seen in their tartens for clan identity. (They also used plant pigments for other colors.) Native Americans traditionally use lichens for dyes in their Chilkat blankets, and as occasional winter food.
Some lichen species are used medicinally, such as for their antibacterial and antifungal properties. They also have been used as a packing material—and sometimes by model train enthusiasts as “vegetation” to simulate shrubs and trees in the landscape.
Figure 5: Parmotrema perlatum (foliose) on a Japanese witch-hazel in the Witt Winter Garden.
A Short Lichen Tour of the Arboretum
Following is a short, self-guided tour of lichens in the Arboretum, based on my regular guided walking tours. But first a word of caution: Please do not pick or collect any of the lichens in the Arboretum. They are very delicate and can drop off from trees and shrub when touched. Enjoy them as part of the natural beauty of the park, and for their contribution to its ecosystem health.
1. Start in the parking lot of the Graham Visitors Center. In the northeast corner of the lot, there are three Ceanothus bushes. One (Ceanothus ‘Puget Blue’) is rather old, with few leaves, but on it are a variety of small lichens, exposed to the sun. Included are Ramalina farinacea, Usnea species (fruticose), Evernia prunastri, and Physcia tenella (foliose). It is best to have a hand lens to explore these tiny beginnings of lichens. See Figure 1.
Figure 6: Lobaria pulmonaria (foliose) growing on an azalea along Azalea Way.
2. Walk to the median in the Visitors Center parking lot. On the main trunk of the trees, you will find Parmelia sulcata and Melanelia species (both foliose). These also live on higher branches along with other lichens, such as Usnea species (fruticose) and Hypogymnia physodes (foliose), and lots of crustose species—though you might have to wait for a windstorm to blow down a branch to enjoy the full diversity. See Figure 2.
3. Walk to the arbor on the south patio of the Graham Visitors Center and look up to the rafters. You will see several lichens growing above your head, including Usnea species and Ramalina farinacea (fruticose); Parmelia sulcata, Hypogymnia physodes, and Evernia prunastri (foliose); and large patches of dust lichen (a type of crustose lichen that looks like dust). See Figure 3.
4. At the west entrance to the Visitors Center, you will see two old stumps to the north side of the path. They are covered with lichens of the large genus Cladonia. One of the most common is the pixie cup, Cladonia chlorophaea (fruticose). Another species seen here is Cladonia transcendens, which forms a “club” rather than a cup-shaped fruiting body. If you look carefully, you might notice red tips on these clubs, explaining the lichen’s common name “British soldiers.” See Figure 4.
5. Next, walk towards the Witt Winter Garden. One of the Japanese witch hazels (Hamamelis japonica) on the north end of the garden has an abundance of lichen varieties, including the yellowish-green forked lichen (Hypotrachyna sinuosa) and the ruffle lichen (Parmotrema perlatum), which is grey-green with broad lobes and eye lashes (cilia) on its margins. The best time to see these two lichens is in late fall, winter and early spring, when the foliage on the tree is gone. See Figure 5.
Figure 7: Sticta limbata, moon lichen (foliose), also growing on an azalea along Azalea Way.
6. The next stop is along Azalea Way, where the lungwort lichen (Lobaria pulmonaria) can occasionally be seen in the azaleas (Rhododendron species). Most of these lobarias have fallen from nearby maple canopies during a rain and/or windstorm and become lodged in the azalea branches. They can live in the azaleas for a while, but over a few years, they will start to decompose and disappear. See Figure 6.
7. Also in the azaleas, you will find quite an abundance of the brownish foliose moon lichen (Sticta limbata). Species of the genus Sticta are cyanolichens, meaning the photobiont is a cyanobacteria, which lends the lichen a black, brown or slate color. The cyanobacteria are important in forests, tundra, botanic gardens, and your yard because they add nitrogen to the soil, providing a key nutrient to plants. They can be recognized by the white hairs on their margins and white spots on the lower surface. See Figure 7.
8. Walking north on Azalea Way back toward the Visitors Center, take a left turn onto the path that leads to the historic Willcox Footbridge. On the bridge’s cement and terra-cotta bricks you will see a bright-yellow lichen. This is not a mineral stain, but a living organism, Flavoplaca citrina s.l. (crustose). If you have a hand lens or a phone that can view the lichen closely, you will see that it is dusty or granular in appearance. With a hand lens, you also may see tiny cups or buttons (ascocarps), with reddish orange centers. These contain the spores of the mycobiont (fungus). See Figure 8.
Figure 8: Flavoplaca citrina s.l. (crustose) growing on the Willcox Footbridge. The tiny “cups,” ascocarps,
are reproductive structures, containing the spores of the fungal partner.
9. Heading back toward the Visitors Center along Azalea Way, take a look at the lower branches of the western red cedars (Thuja plicata). Again, with a hand lens, you might be able to see some tiny lichens on the scales of the cedars. Most of these are Physcia tenella (grey) or Xanthoria polycarpa (yellow-orange), both foliose lichens. See Figure 9.
These are just some of the lichens that live in the Arboretum. See below for a longer list. If you find a lichen in the park that’s not on this list, please contact Dr. Katherine Glew at kglew@uw.edu.
Katherine Glew, Ph.D., is the Affiliate Lichen Curator at UW’s Burke Museum of Natural History. She leads regular tours of the lichens in Washington Park Arboretum.
Figure 9: Lichens growing on the scales of a western red cedar near the Visitors Center, including Xanthoria polycarpa and Physcia tenella (both foliose), and a Lecanora species (crustose). The photo was taken with a macro lens at the same magnification you’d get from a hand lens.
Why You Should Like the Lichens at the Arboretum
- Lichens indicate cleaner air. Enjoy a deep breath!
- Lichens can be habitat and food for animals, including birds, mammals, and invertebrates. They attract animals into the gardens.
- Lichens are part of the natural world that we all appreciate when we visit a botanic garden.
- You can dye wool with lichens. But please do not collect them at the Arboretum!
- 10 percent of all lichens can add nitrogen, one of the important plant nutrients, to the soil.
- When lichens fall to the ground and decompose, they naturally add nutrients and minerals to the soil.
- Lichens are artful, aesthetically pleasing on azaleas, rhododendrons, and many of the trees and shrubs in the park.
Commonly Observed Lichens in the Arboretum
Aspicilia contorta – sidewalk lichen
Bacidia sp. – black dot lichen
Caloplaca sp. – fire dot, gold or orange lichen
Chrysothrix granulosa – gold dust
Cladonia chlorophaea – pixie cups
Cladonia fimbriata – trumpet cup lichen
Cladonia transcendens – British soldiers
Evernia prunastri – antler or oakmoss lichen
Flavoplaca cintrina s.l. – lemon or jewel lichen
Hypogymnia physodes – monk’s hood or tube lichen
Hypogymnia tubulosa – tube or bone lichen
Hypotrachyna sinuosa – forked lichen
Lecanora sp. – rim lichen
Lecidea sp. – black dot lichen
Lepraria sp. – dust lichen
Lobaria pulmonaria – lungwort
Melanelia spp. including Melanelixia glabratula – camouflage lichen
Ochrolechia sp. – belly-button, saucer, pumpkin pie lichen
Parmelia hygrophila – western shield lichen
Parmelia sulcata – wax paper lichen
Parmotrema perlatum – ruffle or dog lichen
Peltigera membranacea – dog lichen, membranous dog or veined lichen
Pertusaria sp. – wart lichen
Physcia tenella/adscendens – rosette lichen
Physcia alnophila – hoary rosette lichen
Platismatia glauca – rag lichen
Ramalina farinacea – Ramalina
Rinodina sp. – Rinodina
Sticta limbata – moon lichen
Sticta fuliginosa – peppered moon lichen
Tuckermannopsis (Cetraria) chlorophylla – silver-lined or powdered wrinkle lichen
Tuckermannopsis (Cetraria) orbata – variable ruffle lichen
Usnea pacificana – old man’s beard or Pacific beard lichen
Usnea subfloridana – old man’s beard or common beard lichen
Verrucaria sp. – black rock lichen
Xanthoria candelaria – candleflame, orange, orange wall, sunburst lichen
Xanthoria polycarpa – orange or sunburst lichen
NOTE: “sp.” — a single species (yet to be identified) within the genus; “spp.” — multiple species present.
RESOURCES
USEFUL BOOKS
- McCune, B. & Geiser, L. Macrolichens of the Pacific Northwest. Oregon State University Press, Corvallis: 2023.
- Brodo, I.M. et al. Lichens of North America. Yale University Press: 2001.
- Lücking, R. Spribille, T. The Lives of Lichens: A Natural History (The Lives of the Natural World, 10). Princeton University Press. 2024.
- Purvis, O.W. Lichens. Smithsonian Institution Press. 2000.
MAGAZINE
Droker, R. Lichens, A Photo Essay. Washington Park Arboretum Bulletin. Vol. 71, number 3, pages 3–9. Fall 2009.
POSTER
Celebrating Lichens. 2016. US Forest Service, United States Department of Agriculture. FS-1071.
WEBSITES
- Lichens of the Pacific Northwest. Based on book by Bruce McCune. Maintained by Oregon Digital, Oregon State University, Libraries & Press.
- Common Macrolichens of the Pacific Northwest, maintained by Dr. Bruce McCune and Sunia Yang.
- North American Lichen Checklist. Esslinger, T. L. & C. A. Morse. 2026. “A cumulative checklist for the lichen-forming, lichenicolous and allied fungi of the Continental United States and Canada, version 25.” Opuscula Philolichenum 25: 45–384.
- Northwest Lichenologists
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This article is reprinted from the summer 2026 issue of the Arboretum Bulletin, our quarterly botanical and horticultural magazine. Published since 1937, the Bulletin is a benefit of Arboretum Foundation membership and features in-depth articles on the Arboretum collections and history, as well as general information of interest to plant lovers in the Pacific Northwest and beyond. Join/subscribe today.
