British Soldiers Lichen

British Soldiers Lichen is among the most instantly recognisable lichens of eastern North America, named for the bright red 'coats' at the tips of its pale stalks, likened to the uniforms of eighteenth-century British infantry. Colonies of hundreds of these tiny red-tipped columns can carpet the top of a decaying stump.

It is a member of Cladonia, the enormous genus of cup and stalk lichens, and shows the classic two-part Cladonia architecture: a primary thallus of small leafy scales called squamules pressed to the substrate, and secondary upright stalks, the podetia, rising from it. In this species the podetia are unbranched or sparingly branched and end in blunt heads rather than open cups.

The red pigment, an acid called rhodocladonic acid, is confined to the apothecia, and it is intense enough to be visible from some distance. Because the species prefers rotting wood and acidic soil in open sunny places, it is a common find on old fence posts, split-rail fences, weathered boards and pine stumps.

Primary thallus

At the base sits a mat of small squamules — irregular leafy scales 1–3 mm long, grey-green above and white beneath, often with slightly upturned, crinkled or lobed edges. This basal layer persists throughout the life of the colony and is a defining Cladonia character.

Podetia

From the squamules rise podetia 5–20 mm tall and about 1 mm thick, greenish-grey to pale grey-green, unbranched or forking once or twice near the top. They are usually rough or granular with tiny scales and granules along their length, and are not hollow-cupped at the tip; instead the summit is blunt, expanded or slightly knobbly.

Apothecia

The defining feature is the apothecium: a bright scarlet to blood-red convex knob 1–2 mm across sitting on the tip of the podetium, sometimes lumpy or several fused together. The colour is strongest in fresh, damp material and can fade to duller brick red in old, sun-bleached colonies.

Chemistry and habit

The lichen typically shows a yellow reaction to potassium hydroxide and a red reaction to para-phenylenediamine. It grows gregariously, dozens to hundreds of podetia together, so a colony reads as a red-speckled grey-green crust across the top of a stump or the upper edge of a rail.

This lichen favours decaying wood and acidic mineral soil in open, sunny to lightly shaded sites: old stumps, fallen logs in advanced decay, weathered fence rails and posts, the tops of split-rail fences, wooden shingles, peaty soil, sandy banks, and the bases of trees. It also grows over mosses on rock outcrops. It avoids limestone and enriched ground.

It is characteristic of eastern North America, from the Canadian Maritimes and Great Lakes south through the Appalachians to the southeastern coastal plain, extending west across boreal Canada, with related reports in East Asia. Perennial and evergreen, it is visible year-round, though the red apothecia look brightest after rain and in the growing season, and podetia may bleach in prolonged summer drought.

Like all lichens this is a composite organism: the fungal partner constructs the squamules and podetia, while green algal cells in a layer beneath the surface photosynthesise. Nutrients and water are taken directly from rainfall, mist and the surface of the decaying wood, so it can occupy substrates far too poor and acidic for vascular plants.

Ecologically it is part of the community that colonises wood in the later stages of decay, contributing to the slow breakdown of stumps and rails and adding organic matter as old podetia disintegrate. It is an early coloniser of disturbed acidic ground such as burned areas, sandy cuts and abandoned clearings. Reproduction is by ascospores from the red apothecia and, more commonly in practice, by fragments of squamule and podetium carried by rain, wind and animals. The bright red pigmentation may help screen the algal layer from strong light in the open sites the species prefers.

Several red-fruited Cladonia species look similar. Cladonia macilenta, the lipstick powderhorn, has slender podetia densely coated in fine powdery soredia, giving a floury surface, whereas Cladonia cristatella is granular-scaly rather than powdery. Cladonia bellidiflora is a montane species with podetia heavily covered in leafy squamules and larger red apothecia. Cladonia floerkeana, the devil's matchstick, has smoother, more sparsely granular podetia and typically smaller, more discrete red knobs.

Cladonia didyma and other tropical or southern red-fruited species differ in podetium surface and chemistry and need spot tests to separate reliably. The cup-forming Cladonia species — pixie cups, trumpet lichens, powderhorns — are told apart at once because their podetia open into hollow goblets or taper to a point without any red tip, and their apothecia, when present, are brown rather than scarlet. Any lichen with a red tip on an upright stalk over a mat of grey-green squamules is in this group, and the surface texture of the stalk is the main separator.