Ragbag Lichen Identification Guide

First impression and setting

Ragbag Lichen looks exactly like its name: a loose, ragged, grey-green sheet that appears to have been torn along every edge. You meet it in humid forest — coastal and upland conifer stands, birch woods on damp hillsides, old orchards and hedgerow ash — draped over branches and small twigs, sometimes wrapping a whole limb, sometimes hanging half-detached and turning in the wind. Because it holds on so loosely, wind-fallen pieces litter the ground after a gale, and picking one up off the track is often how people first examine it closely. It also grows on the flanks of rough-barked trunks, on fence rails, on old lignum, and on shaded acidic boulders in the same climate zone.

Reading the lobes

Start with the overall architecture. This is a foliose lichen — leaf-like, with a distinct top and bottom, growing in loose rosettes or irregular sheets 5–20 cm across. The lobes are broad, generally 1–3 cm wide, rounded and irregular in outline, and they overlap untidily rather than radiating in a neat pattern. The lobe surface is undulating, with shallow ridges and hollows, and the margins are the giveaway: they turn upward, become wavy and crisped, and then split and fray into a fringe of tiny leaf-like flakes and granules. That fraying is what gives the whole thallus its shredded, secondhand-clothes appearance.

Reading colour, texture and the underside

The upper surface is pale grey to bluish-grey when dry, sometimes almost white on exposed branch tips, and it turns noticeably greener and softer when wet. Dry, the thallus is stiff, brittle and chalky to the touch and snaps if you bend it; soak it in a puddle for a minute and it becomes limp and leathery. That transformation is worth trying, because several lookalikes remain firm and papery when wet.

Turn a lobe over. The underside is black in the older, central parts, grading through mottled dark brown to pale buff towards the lobe tips, and it is smooth to slightly wrinkled. Crucially, it is bare: there are no dense rhizines, only occasional scattered holdfasts at a few points of attachment. This is why the lichen sits so loosely on its branch, and the absence of a rhizine mat is one of the strongest single characters.

Propagules and fruiting bodies

Run a lens along the ridges and lobe edges. Platismatia glauca reproduces mostly by vegetative fragments, and populations differ in which type they favour. Some are dominated by isidia — tiny, solid, cylindrical to coral-like outgrowths that keep the cortex intact and feel granular. Others are dominated by soredia — powdery to granular masses of loose algal cells wrapped in fungal threads, produced where the cortex ruptures along the margin. Many thalli show both. Either way the products are the same in outline: a crumbly, granular fringe along the edges and ridges.

Apothecia, the disc-shaped sexual fruiting bodies, are genuinely rare in this species. When present they are small, brown, and set on the lobe margins rather than on the flat face.

The spore print question

There is no meaningful spore print to take from a lichen, and with apothecia so uncommon you will usually never see a spore at all. If you do find fertile material, the equivalent procedure is a squash mount: shave a thin slice through the disc with a razor, mount it in water on a slide, and press it gently under a coverslip. The asci each contain eight simple, colourless, ellipsoid ascospores of roughly 5–9 by 4–6 µm.

A vertical section through the thallus is far more instructive for identification. It shows a compact upper cortex, a bright green band of algal cells just beneath it, a thick white cottony medulla of loose fungal threads, and a dark lower cortex. Chemical spot tests can be applied to that section: the upper cortex reacts K+ yellow, while the white medulla stays unreactive to K, C and P — a combination that quietly rules out several grey foliose genera.

Substrate, climate and ecology

The partnership here is between a fungus and a green alga of the genus Trebouxia, and the whole organism depends on frequent wetting from rain, fog and dew. That is why it is abundant in oceanic and montane forests with high humidity and scarce in dry, continental interiors and in heavily polluted air. It is an epiphyte, using the branch only as a perch rather than drawing anything from the tree, so it does no damage to its host. Its loosely attached fragments are readily blown or knocked free, and those pieces will re-establish where they land, which makes wind an effective dispersal agent. Dislodged thalli are collected by birds and small mammals as nesting material, and the whole epiphyte layer contributes to canopy nutrient cycling when it falls and decomposes.

Separating the lookalikes on structure

Parmelia sulcata is the commonest confusion. It is a similar grey, but it lies tightly against the bark, its upper surface is crossed by a distinctive white network of ridges and cracks, its soredia form in tidy lines along those cracks, and its underside is black with a dense mat of branched rhizines. The tight attachment and rhizines are decisive.

Hypogymnia physodes shares the loose habit and rhizine-free underside, but its lobes are inflated and hollow — pinch one and it collapses like a small balloon — and its soredia burst from the undersides of upturned lobe tips.

Platismatia tuckermanii has the same ragged build but produces abundant marginal brown apothecia and few or no soredia, and its thallus tends browner.

Platismatia norvegica is coarser, with a bold network of raised ridges and deep cracks across the lobe surface.

Pseudevernia furfuracea is strap-like and more three-dimensional, with a sharply two-toned black-and-white underside and dense isidia scattered across the whole upper face rather than confined to the margins.

Punctelia and Cetrelia species are broad-lobed and grey but carry conspicuous white pseudocyphellae as scattered dots or specks on the upper surface.

Usnea and Ramalina are fruticose — round or strap-shaped and branching in three dimensions with no distinct upper and lower surface — so they drop out on growth form alone.

Field summary

Loose grey-green foliose sheets on conifer or birch branches in a humid forest; broad wavy lobes with upturned, torn, crisped margins bearing granular isidia or soredia; bare black-to-brown underside with almost no rhizines; brittle when dry, limp and greener when wet; apothecia rare. That is Ragbag Lichen.