Firedot Lichens (Caloplaca Lichens)

Closeup of firedot lichen on a tombstone
Scientific Name
Caloplaca spp.
Family
Teloschistaceae (a lichen family)
Description

Firedot lichens are usually orange, yellow, rusty, or brown and look like tiny dots on a surface. There may be no obvious differently colored base (that is, the main body, or thallus), and only the dots may be visible. These dots are the spore-bearing structures (apothecia). To see these crustose lichens well, you often must get on your hands and knees and use a hand lens.

There are more than 125 species of firedot lichens (Caloplaca spp.) in North America, and Missouri has 23. Many are tiny, but groups of them can cover large areas on rocks or tombstones. Some species grow on tree bark or bare wood.

Despite the name, some in this genus are not very “fiery” — several species are light gray with dark gray, black, or dark brown dots.

Also, some firedot lichens grow in round patterns with edges that are so wrinkled that they appear foliose; then the centers may die and fleck away, leaving the rounded outline.

Like other crustose lichens, firedot lichens are tightly attached to the substrate they grow on. Their main bodies often look like a patch of paint (a faint spritz or thick, old, and weathered), and the surface may looked cracked or bumpy. Along the perimeter, there may be a dark outline, especially where two lichens meet.

A lichen is an organism that results when a fungus species and an algae species join together. Although the relationship between the fungi and algae is quite intimate and integrated, the lichen that is formed does not much resemble either of the components. Learn more about lichens on their group page.

Similar species:

  • Goldspeck lichens (Candelariella spp.) are orange-yellow crustose lichens that are frequently seen growing on rock outcrops, tombstones, and other rocky substrates.
  • Orange sunburst lichens (Xanthoria or Xanthomendoza species) can be very common on sunny rocks and tombstones. They have a circular, foliose growth pattern with tiny, branching lobes, but this pattern often becomes obscured when these lichens coalesce into large masses of tiny scale-like fragments and portions break off. For this reason, it could easily be misinterpreted as a crustose lichen.
  • Candleflame lichen (Candelaria concolor), is very small, at most only about the size of a fingernail, although it often grows in groups covering large areas. Candleflame lichen almost always grows on bark and is a greenish (not orangish) yellow. Numerous granular soredia form at the thallus tips, making it look frilly at the tips. It is a foliose lichen, and you can usually see the rosette pattern, with branching, petal-like lobes, if you look closely. The similar-looking Candelaria fibrosa is also present in Missouri.
Other Common Names
Orange Lichens
Size

Lichens begin as tiny spots but may grow to cover several square inches. Groups of firedot lichens may coalesce to cover large areas.

Where To Find

Statewide.

Firedot lichens occur in sunny locations on cement sidewalks, gravestones, mortar, and limestone boulders and outcrops; in Missouri, look for them on glades. Some species grow on tree bark or bare wood.

Firedot lichens may be easiest to see after a rain, or on a sunny day in early spring when snow is melting, when sidewalks, retaining walls, rocks, and rock faces darken and the wet lichen's color intensifies.

Common. Often overlooked.

Lichens contribute to a beautiful landscape. In desert, alpine, tundra, or other rocky habitats, they can coat rocks with a riot of bright colors — neon yellows, oranges, and greens — which intensify after a rain. In Missouri, good places to see lichens on rocks include glades and the open, rocky tops (balds) of Ozark hills. Visit places like Taum Sauk Mountain, Elephant Rocks State Park, Wildcat Glades, and Lichen Glade Conservation Area.

Look for firedot lichens on sidewalks, retaining walls, and other concrete or stone surfaces. Maybe you will spot their tiny orange apothecia cups in a mundane place on a drab, late winter day. It can uplift you during your lunch hour. Hello, little firedots!

Media Gallery
Closeup of firedot lichen on a tombstone
Firedot lichens (Caloplaca spp.) are crustose lichens that are very common on rocks, sidewalks, and tombstones. This pretty orange specimen was growing in a sunny place on a tombstone.
Julianna Schroeder
1/10
Lichen
David Bruns
2/10
Patches of firedot lichens growing on a rock
Crustose lichens often look like a little squirt of spray paint on a surface. You have to get close to see the tiny cups or other reproductive structures. Note how individual crustose lichens often form black lines on the boundaries where they meet.
Julianna Schroeder
3/10
Firedot lichen, possibly Caloplaca flavovirescens, on a rock at Painted Rock CA
This firedot lichen might be Caloplaca flavovirescens. This closeup shows how closely integrated it is with the rock it's growing on. Note also the dark line that forms where two of these lichens touch each other.
Julianna Schroeder
4/10
Firedot lichens growing in circles on a tombstone
These firedot lichens (Caloplaca sp.) are growing in circular patterns on a tombstone. The tiny dots are actually the spore-bearing structures, called apothecia. The main body of the lichen (thallus) grows on the surface beneath and around the apothecia.
Julianna Schroeder
5/10
Colony of firedot lichens (Caloplaca sp.) on a boulder at Lake Ozark State Park
These firedot lichens (Caloplaca sp.) decorate a boulder overlooking the Lake of the Ozarks.
Julianna Schroeder
6/10
Firedot lichens growing on a marble tombstone
Firedot lichens (Caloplaca sp.) growing on a marble tombstone.
Julianna Schroeder
7/10
Firedot lichens on a tombstone
Because some firedot lichens can grow and coalesce to the point where the edges wrinkle and start flaking away, they could easily be mistaken for foliose lichens.
Julianna Schroeder
8/10
Firedot and orange sunburst lichens growing on a tombstone
Common tombstone lichens include firedot lichen (Caloplaca sp.) (the crustose lichen at center) and orange sunburst lichen (Xanthoria sp.) (the foliose, branching, more yellow lichen at upper right).
Julianna Schroeder
9/10
Firedot lichens with wrinkled edges, appearing foliose, on a tombstone
Some firedot lichens grow in round patterns and develop edges that are so wrinkled that these crustose lichens may appear foliose. The centers may die and fleck away.
Julianna Schroeder
10/10
Closeup of firedot lichen on a tombstone
Lichen
Patches of firedot lichens growing on a rock
Firedot lichen, possibly Caloplaca flavovirescens, on a rock at Painted Rock CA
Firedot lichens growing in circles on a tombstone
Colony of firedot lichens (Caloplaca sp.) on a boulder at Lake Ozark State Park
Firedot lichens growing on a marble tombstone
Firedot lichens on a tombstone
Firedot and orange sunburst lichens growing on a tombstone
Firedot lichens with wrinkled edges, appearing foliose, on a tombstone
Similar Species
About Mosses, Liverworts, and Lichens in Missouri

Mosses, liverworts, hornworts, and lichens seem rather similar, but these organisms are in very different groups. Mosses, liverworts, and hornworts are small, low plants usually found in damp habitats. Unlike more familiar plants, they lack veinlike structures and do not produce flowers or seeds — instead, they produce spores. Meanwhile, lichens are not plants at all: they are a collection of different fungi that have photosynthetic algae living within their tissues.

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