Common Powderhorn Lichen

The Common Powderhorn is one of the most widespread lichens of wooded country, forming pale grey-green fuzz on the lower trunks of trees, on stumps and on rotting logs. Its podetia are slim, slightly curved, and taper toward the tip like small horns or awls — hence the name — rather than opening into the goblets of its cup-forming relatives.

Cladonia coniocraea is a Cladonia, built in the genus's characteristic two storeys: a persistent primary thallus of small leafy squamules pressed against the bark or wood, and secondary upright podetia rising from that mat. In this species the basal squamules are often conspicuous and long-lived, forming a green-grey scaly crust from which the horns emerge.

Its most useful character is the dense coating of farinose soredia — a fine, pale, flour-like dust — over almost the whole podetium. Combined with the tapering, blind-ended tips and its strong preference for tree bases and decaying wood, that powdery surface makes it recognisable even to a beginner working with a hand lens.

Primary thallus

Basal squamules are 2–6 mm long, grey-green to olive-green above and white beneath, elongate and often finely lobed or crenulate, with margins that may be slightly raised. They form dense, persistent mats over bark, mossy wood and soil, and are usually much more evident than in some other Cladonia species.

Podetia

Podetia are 5–30 mm tall, slender (about 0.5–1.5 mm thick), unbranched, and taper gradually to a blunt or narrowly pointed tip. They are frequently slightly curved or leaning rather than perfectly upright. Cups are rare; when they form at all they are very narrow, off-centre and irregular, more of a slight opening than a true goblet.

Surface

The podetium is coated over most of its length in fine, powdery farinose soredia, pale grey-green to almost white, giving it a soft, matt, mealy appearance. Small squamules may be scattered near the base of the podetium, but the upper part is essentially all powder.

Apothecia and chemistry

Apothecia are uncommon: small pale to dark brown discs at the tips, never red. Potassium hydroxide is negative to weakly yellow; para-phenylenediamine gives a red reaction (fumarprotocetraric acid), which is a useful confirmation within the genus.

This is above all a lichen of tree bases and decaying wood. It is typically found on the lower trunks of conifers and broadleaf trees, especially where bark is acidic and rough, on old stumps, fallen logs in mid to late decay, mossy roots, fence posts and boards, and on peaty or humus-rich acidic soil among mosses. It tolerates shade well and is common inside woodland rather than only at its edges.

It is widespread across the northern hemisphere — throughout Europe, boreal and temperate Asia, and North America from the boreal forest to temperate lowlands — and is one of the commonest lichens on tree bases in many regions. Perennial and evergreen, it can be found in any month, with soredia produced abundantly and podetia developing during moist periods through the growing season.

The lichen is a symbiosis in which a fungal partner constructs the squamules and horn-shaped podetia while green algal cells beneath the surface photosynthesise. Nutrients and moisture come directly from rain, throughfall running down tree trunks, and humidity, which suits the sheltered, damp microclimate at the base of a trunk where it typically grows.

It is a significant part of the epiphytic and wood-decay lichen community, colonising bark and rotting timber that is too acidic and nutrient-poor for many competitors, and adding organic matter as older thalli break down. Its abundant soredia are its main means of spread: these composite propagules contain both fungus and alga and are dislodged by rain splash, wind and passing animals, allowing rapid recolonisation of new stumps, exposed roots and freshly fallen wood without the delay of pairing spores with a suitable alga. It is moderately sensitive to nitrogen enrichment and is often used in surveys of woodland air quality.

Cladonia fimbriata, the trumpet lichen, shares the fine floury soredia but reliably forms a neat, regular, gradually flaring cup at the top of each podetium; the Common Powderhorn tapers to a point and at most manages a narrow, irregular, off-centre opening. Cladonia ochrochlora is extremely close, differing in having a partly corticate (smooth, non-powdery) zone at the base of the podetium and often slightly stouter stalks — the two are frequently confused.

Cladonia macilenta, the lipstick powderhorn, has a similar slender sorediate podetium but is topped with bright red apothecia; the Common Powderhorn's fruiting bodies are brown. Cladonia pyxidata and Cladonia chlorophaea are coarser, granular rather than floury, and form obvious wide goblets. Cladonia squamosa has podetia clothed in conspicuous leafy squamules instead of powder. Where podetia are absent altogether, the persistent mat of elongate grey-green squamules on a tree base is itself a good pointer to this species.