Approximately 86 percent of Everglades National Park has been designated the Marjory Stoneman Douglas Wilderness. As the largest wilderness east of the Rocky Mountains and the only subtropical wilderness in the United States, this wilderness offers a unique opportunity to study, document, and preserve lichens.

Lichens exist in every terrestrial habitat within Everglades National Park and on all substrates, such as tree bark, rock, leaves, and soil. Although Everglades National Park is known for its extensive sawgrass marshes, lichen diversity is richest where trees are present. Tree islands and cypress domes visible from the main park road provide excellent habitat for native lichens. Other forested communities such as tropical hardwood hammocks and mangroves also support a large lichen flora. Casual viewers typically see lichens as a constituent of tree bark. Lichens even grow on manmade substrates, such as on asphalt and concrete in parking lots, along roadsides, and in developed areas. Close inspection reveals a special lichen world unique to subtropical Florida.

What Lichens Are

Lichens cannot be classified as a single entity like plants because they are a composite of fungi (lichen’s mycobiont) and green algae or blue-green algae (cyanobacteria) (lichen’s photobiont). Alga are capable of producing food by photosynthesis but fungi cannot produce their own food. In this special biological relationship the fungus provides a protective exterior surface for the alga. This enables the alga to exist in full sun thus maximizing its ability to produce food for both. This mutually beneficial relationship is called symbiosis, although many now consider it a controlled parasitism of the photobiont by the fungus. Lichens carry the name of the fungal lichen partner.

What Lichens Look Like

A bewildering variety of color and form are found in the lichens of Everglades National Park. Lichens can look like little shrubs, drape tree limbs like Spanish moss, or appear as little dots, lines, or smudges. Their color range is wide and includes red, yellow, green, gray, and white. Many are very small but others can cover large areas. For taxonomic purposes they are divided into four growth forms: crustose (crust-like), foliose (leafy), fruticose (shrubby), and squamulose (scale-like).

Crustose lichens are the most common form present in Everglades National Park and in other subtropical and tropical regions of the world. They are distinguished by their tight adherence to substrate, which makes it impossible to remove them without including part of the substrate. Taxonomically they are divided into numerous groups on the basis of fruiting body shape and internal structure.

Identification of crustose lichens involves viewing the external and internal structure of lichen fruiting bodies through microscopes. External features can be viewed with a low-magnification inspection scope, and internal structures such as spores and asci (sac-like cells containing ascospores) can be viewed with a higher-magnification compound scope. Identification also involves testing the chemical composition of lichens with Thin Layer Chromotography. These methods are time consuming but simple in comparison with interpretation of the results. Reference material is scattered worldwide, often difficult to obtain, and expensive or not available at all.

Foliose lichens are leafy in appearance and loosely attached to the substrate. The top side is easily distinguishable from the bottom side. They can be flat, leafy, or convoluted, and can contain multiple ridges and bumps.

Fruticose lichens are typically the most glamorous and showy. The word “fruticose” is a technical term meaning “shrubby” and has nothing to do with fruit. This shrub-like growth form is the most highly developed and plant-like of the four forms, and some species of fruticose lichen can be difficult to tell apart from plants. Fruticose lichens often appear to be miniature shrubs. They are often densely branched and the most three-dimensional, often with a single point of attachment to the substrate.

The growth rate of lichens is variable and depends on multiple factors, including the species of lichen. Substrate is also important; a lichen growing on organic tree bark teeming with nutrients will grow at a different rate than a lichen growing on an inorganic solid rock. Growing conditions, such as climate and amount of sunlight, also affect the growth rate.

Squamulose lichens have scale-like lobes called squamules that are typically small and overlap to form mats. The squamules are attached to their substrate at one end, like a tiny shingle. Squamulose lichens are similar to crustose lichens at the base, with leaf-like squamules that are lifted up off of the substrate. The growth form of squamulose lichens is intermediate between that of crustose and foliose lichens. Because of the similarities in small size and stature, crustose and squamulose lichens are generally grouped together as microlichens. The larger foliose and fruticose lichens are generally grouped together as macrolichens.

Some species of lichen are combinations of the fruticose and squamulose growth forms. The “fruticose” stalks of Cladonia cinerella (see photo at left) develop from a “squamulose” base. Although many species of crustose lichens are conspicuously lobed at their margins and appear to be foliose, they are classified as crustose because they are in intimate contact with their substrate over most of their lower surface. Similarly, some species of foliose lichens are so tightly attached to their substrate that a microscope is needed to check to make sure that the lichen is indeed foliose.

U.S. Dept of Interior