Maryland Grows

The wet, gray days at the end of winter seem like they may never end. But this is actually the perfect time of year to get out and appreciate those mysterious ‘plants’ encrusting everything from sidewalks to treetops – the lichens.

There is a lot to be said for simply enjoying the natural beauty of lichens without trying to label them. However, lichens are easier to identify, at least to the family level, than you might think.

If you can distinguish soil, rock and tree bark, you are off to a running start. Different lichen species specialize in growing on these three types of substrate, so this is an important first clue to a lichen’s identity. Hunting for lichens at this time of year is facilitated by the general lack of foliage, making bare soils, rock outcrops, and tree trunks more visible than usual.  As a special bonus, storms have littered the ground with lichen-encrusted branches, revealing treasures that would normally be above our reach. Even small branches can host several species, each with its own unique color and shape.

Body shape is another clue that is easily understood by beginners. Lichens occur as either:

• Powdery, crusty colors on surfaces, reminiscent of spray paint.
• Flat leafy shapes, usually rounded in outline.
• Three-dimensional shapes reminiscent of shrubs, beards, cups, etc.
• Color is another easy clue, and it is during gray, wet weather (typical of March) when lichens are most colorful. During dry spells, lichens shrivel up and their surfaces become opaque and faded-looking. This protects the internal, photosynthesizing algae from desiccation. When re-moistened, lichens expand and their surfaces become transparent again. Light and moisture can reach the internal algae, and photosynthesis resumes. The algal colors, which are often brighter than that of the fungal surface, shine through.

Lichens produce special structures for dispersing their progeny, and these result in interesting changes in shape, texture, and color which are further clues to a lichen’s identity. The reproductive lives of lichens are unique, involving asexual methods, as well as sexual reproduction of the fungal symbiont. As with many things botanical, these structures have intimidating names like insidia, soredia, and apothecia. Fortunately, it is not necessary to remember the names of the dispersal structures to use them successfully as taxonomic clues.

The life cycles of many native animals are intricately tied to lichens. Here are a few examples from animals native to Maryland:

• Ruby-throated hummingbirds line their nests with strips of lichen.
• Painted lichen moth caterpillars can only eat lichens.
• The green leuconycta protects itself from predators by looking like lichens.
• A predator, the giant lichen orbweaver camouflages itself against lichens.

Lichens also have many other stories to tell, intertwining their presence in almost all aspects of ecology and human endeavor. Here are but a few examples that illustrate their importance:

• Approximately 8% of the terrestrial earth is covered by lichens.
• Lichens absorb nutrients from the air and can be used as air quality indicators.
• Lichens contribute nitrogen and minerals to the ecosystems in which they occur.
• Historically, humans have used various species of lichens to make dyes and medicines.
• Lichens produce unique biochemicals to fend off herbivores, prevent freezing, and stop seeds from germinating in their soft, moist tissue. These chemicals hold promise for the development of new medicines and agricultural chemicals.

By Sara Tangren, Ph. D
Agent Associate | Master Gardener Trainer | Sustainable Horticulture and Native Plants

Do you have concerns about lichens on landscape plants? Don’t worry! They do not harm plants. See Lichens-Trees & Shrubs on the Home & Garden Information Center website.