Candleflame Lichen Identification Guide

What You Are Looking At

The Candleflame Lichen is not a mushroom in the everyday sense, and adjusting your expectations is the first step to identifying it. It is a lichen: a partnership between a fungus and a green alga, growing as a small persistent crust on bark rather than as a fruit body that appears and rots away in a week. It is present all year, it does not have a cap or a stem, and almost everything diagnostic about it happens at a scale of a fraction of a millimetre. Bring a hand lens of at least ten times magnification, and preferably twenty.

The typical encounter is on a street tree, a roadside maple or ash, a hedgerow elm, an old orchard apple, or a fence post or wall in the open. You notice a scattering of small bright yellow patches on the bark, each one a rosette a centimetre or two across, sometimes merging into a broader yellow wash across a branch. From a few metres away it looks like a spray of yellow dust or a small candle flame caught on the trunk.

Reading The Thallus

Get the lens on it and the structure resolves. The body of the lichen, its thallus, is foliose in the technical sense but only just: it is built of minute leaf-like lobes rather than being an undifferentiated crust.

The lobes are tiny, typically 0.2 to 0.5 mm wide, and they are deeply and repeatedly divided so that each rosette is a filigree of narrow fingers. The lobe tips ascend, curling up and away from the bark rather than lying flat against it, which is what gives the colony its fluffy, tufted, flame-like appearance. Toward the centre of a rosette the lobes crowd and pile up into a small cushion. The upper surface is bright egg-yellow to greenish-yellow, paler in heavy shade and brighter in strong light.

The Soredia

The crucial character is the granular material on the lobe margins and tips. This lichen reproduces mainly by soredia, tiny powdery packets that each contain both fungal threads and algal cells and can start a new colony wherever they land.

Under the lens the margins and especially the ascending tips of the lobes are crumbling into a fine yellow granular powder. In well-developed material the soredia are so abundant that the edges of every lobe look frayed and mealy, and the whole rosette takes on a slightly out-of-focus, fuzzy outline. Turn the lens on a single lobe and try to see where the intact surface ends and the granules begin, because the distribution of soredia along the lobes is one of the characters used to separate this species from its nearest relative.

The Lower Surface And Attachment

Gently lift a lobe at the edge of a rosette with a needle or the point of a knife. The lower surface is white to pale cream, and it bears sparse, short, pale rhizines, root-like anchoring threads that attach the lichen to the bark. The presence of a distinct pale lower surface with rhizines is what makes this a foliose lichen rather than a crustose one, where the thallus is fused to the substrate with no separable underside.

The Spore-Bearing Structures

There are no gills, pores or teeth here, and no mushroom-style fruit body. When this lichen does produce sexual structures they are apothecia: small disc-shaped cups sitting on the thallus surface, usually less than 1 mm across, with a yellow to yellow-orange disc surrounded by a rim of thallus-coloured tissue. In many populations apothecia are scarce or absent, because the soredia do most of the propagation, so do not expect to find them on every colony. Scan the centres of the larger rosettes, where they are most likely.

Why There Is No Spore Print

The spore print, the standard tool for gilled mushrooms, does not apply here. In an agaric you cut a cap and let a large, downward-facing fertile surface shed millions of spores onto paper overnight. On this lichen the fertile surface is a handful of minute upward-facing discs embedded in a crust glued to bark, so there is nothing to invert and nothing to shed a visible deposit.

What replaces it is direct examination. Slice a single apothecium with a razor blade, mount the section in water on a slide, and look at the spore sacs. In this family the sacs characteristically contain far more than the usual eight spores, often dozens, and the spores themselves are small, colourless, simple ellipsoids without cross walls. That polysporous condition is a strong family-level confirmation.

The field equivalent of a spore print here is a chemical spot test. Put a small drop of dilute potassium hydroxide solution on the yellow thallus surface under the lens and watch. In this species there is no colour change: the yellow stays yellow. That negative result is diagnostic against a whole group of look-alikes, as described below.

Substrate, Ecology And Season

This lichen has a strong preference for bark that is enriched with nutrients: roadside trees receiving splash and dust, trees in farmyards and pastures where animals gather, orchard trees, and trunks below perching branches. Maple, ash, elm, poplar, oak and fruit trees are all typical hosts. It also grows on fence rails, wooden posts, concrete, mortar and occasionally rock.

Ecologically it is nitrogen-tolerant and comparatively tolerant of air pollution, which is why it persists in towns and along busy roads where more sensitive lichens have disappeared. It favours well-lit positions and is commonest on the open sides of trunks and on twigs and small branches rather than in deep shade.

Being perennial, it can be found in any month. The best examination conditions come after rain or in damp weather, when the thallus swells, the colour deepens and the lobes flex enough to lift for inspection. Bone-dry material is brittle and easy to damage.

Separating The Look-Alikes On Structure

Candelaria pacifica is the hardest, being extremely similar in colour and size. Work on the soredia and the lower surface: in Candelaria pacifica the soredia tend to be restricted to the lobe tips and the underside is more sparsely rhizinate with a less well developed white lower cortex, while in Candelaria concolor soredia extend along the lobe margins as well as the tips.

Candelariella species are the same yellow but crustose. They form granular or scurfy crusts of tiny yellow grains or minute scales with no lobes, no upturned tips and no separable white lower surface. If you cannot lift an edge with a needle, you are probably in Candelariella.

Xanthoria and Xanthomendoza species are orange rather than egg-yellow, have much larger lobes, and give the decisive test: a drop of potassium hydroxide turns them an immediate deep purple-red. Candelaria does not react at all. This single test separates the two groups instantly.

Physcia and Phaeophyscia species occupy the same enriched bark and often grow intermingled, but they are grey to grey-brown rather than yellow, with broader flatter lobes.

Flavoparmelia and Xanthoparmelia species are yellow-green rather than egg-yellow, and their lobes are enormous by comparison, several millimetres to a centimetre wide, forming broad flat rosettes on bark or rock.

Quick Field Checklist

Bright egg-yellow, tiny rosettes on nutrient-enriched bark, posts and masonry; minute deeply divided lobes 0.2 to 0.5 mm wide with ascending tips; abundant granular yellow soredia along margins and tips; white lower surface with sparse pale rhizines; apothecia small, yellow-orange, often absent; no reaction to potassium hydroxide; present all year, best examined damp.