Hooded Tube Lichen Identification Guide

What You Are Standing In Front Of

Hooded Tube Lichen is one of the commonest foliose lichens of cool temperate woodland, and once you have your eye in you will see it everywhere: grey-green rosettes plastered over spruce and pine bark, spreading along birch trunks, coating the twigs of old apple trees, colonising fence rails, gate posts, wooden benches and occasionally acidic rock. On heavily colonised conifers the branches can look as though they have been dusted with pale grey paint.

The first impression is of a flattish, leafy rosette 3 to 8 cm across, pale greenish-grey to greyish-white above, with narrow, strap-like lobes that overlap and branch repeatedly. Individual thalli merge into one another until the boundaries are hard to trace. Compared with most other grey foliose lichens on the same bark, it looks smoother and slightly inflated, as though the lobes had been gently blown up.

Reading the Lobes

Work with a hand lens from the start. The lobes are 1 to 4 mm wide, contiguous to slightly overlapping, and branch dichotomously into a neat, rather flat rosette. Their surface is smooth, matt to faintly shining, and unbroken: there are no ridges, no white netting and no cracked mosaic across the upper cortex. In older parts of the thallus the surface may become slightly wrinkled or spotted with dark flecks.

Colour is grey to greenish-grey when dry, becoming distinctly greener and more supple when wet. Carry a small water spray if you can; wetting a lichen for thirty seconds transforms its colour and texture and makes the surface characters far easier to read.

Feel the lobes gently between finger and thumb. They are slightly puffy rather than solid. This is the diagnostic feel of a tube lichen, and where the lobes are broadest they are visibly convex and hollow beneath the surface.

The Decisive Character: Lip-Shaped Soralia

Follow the lobes outward to their tips. In this species the tips turn upward and split open along the lower side, and the granular reproductive powder, the soredia, bursts out of the resulting opening. The result looks exactly like a small lip, hood or scoop, with a pale granular mass held in the upturned end of the lobe. This shape is usually described as labriform or lip-shaped, and it is the single most reliable field character for the species.

Look carefully at where the soralia sit. They are on the underside of the flared lobe tip, revealed by that upward curl, and they form a broad crescent or ribbon rather than a neat ball. They are not scattered as patches over the flat upper surface, and they are not perched like a globe on the very apex of an unopened tube. That geometry is what separates this lichen from its nearest relatives.

The soredia themselves are fine and granular, whitish to greenish-grey, sometimes darkening at the edges of older soralia.

Upper and Lower Surfaces

Turn a lobe over. The lower surface is black across most of the thallus, becoming dark brown towards the growing edge, and it is smooth to slightly wrinkled and shiny. Critically, it is completely without rhizines: there are no root-like hairs anchoring it, and the thallus attaches loosely by scattered points on the underside. That bare, hairless black underside is a strong genus-level character and is one of the fastest ways to exclude a whole set of look-alikes.

Cutting a Lobe Open

Take a broad lobe and slice it transversely with a knife or razor blade, or simply squash it flat and tear it. The interior is hollow: a genuine air-filled tube running through the lobe, floored by a dark layer and roofed by the white medulla under the upper cortex. This internal cavity, more than anything, defines the tube lichens, and confirming it in the field takes about five seconds.

Note the medulla colour while you are there: white above the cavity, with the floor of the cavity dark to blackish.

Fruiting Bodies and Spores

Being a lichen, this species has no gills or pores and you will not take a conventional spore print from it. Apothecia are produced but are decidedly uncommon, because the lichen propagates so effectively by soredia. When they do occur they are stalked or shortly pedicellate discs 2 to 6 mm across, with a red-brown to dark brown disc and a thin thalline rim. Each ascus holds eight simple, colourless, ellipsoid ascospores in the region of 6 to 8 by 4 to 5 micrometres.

For practical purposes, the reproductive character you use in the field is the soralia, not the spores. Small black pycnidia may also dot the upper surface as tiny raised points.

Substrate, Habitat and Season

This is a bark lichen above all: conifers such as spruce, pine and larch, and hardwoods including birch, oak, alder and orchard trees. It also colonises worked timber, from fences and posts to shingles and benches, and thin soil over acidic rock, and it will grow on twigs as readily as on trunks. It tolerates a fair amount of atmospheric pollution and disturbance, which is why it is often the first foliose lichen to return to recovering woodland.

Lichens do not have a fruiting season in the way that mushrooms do, so this one is identifiable in every month of the year. Practically speaking, damp weather is best for fieldwork: the thallus swells, greens up and becomes flexible enough to lift and section without shattering.

Separating the Look-Alikes

Powdered Tube Lichen (Hypogymnia tubulosa) is the closest relative and the commonest confusion. Its lobes are narrower, more ascending and distinctly tubular, and its soralia are terminal and capitate: a rounded, ball-like head of soredia sitting on the closed end of the lobe tip, not a lip opening from beneath.

Hypogymnia farinacea carries its soralia as rounded granular patches on the upper surface of the lobes, well back from the tips, and its lobes are flatter.

Hypogymnia bitteri and relatives have soralia developing from cracks along the lobe surface, and the lobes are often browner toward the tips.

Hammered Shield Lichen and Parmelia sulcata superficially resemble it in colour but the underside is densely covered in black rhizines, the lobes are solid rather than hollow, and the upper surface bears a network of white ridges and cracks.

Varied Rag Lichen (Platismatia glauca) is larger and looser, with broad crinkled lobes, soredia and isidia along the lobe margins, and no hollow interior.

Pseudevernia furfuracea has stiff, strap-like, sparsely branched lobes that are dark below and bear coral-like isidia rather than powdery soralia, and it is only loosely attached at one point.

Field Checklist

Grey-green flat rosette on bark or wood; smooth unbroken upper surface; lobes 1 to 4 mm wide, inflated and hollow when cut; lower surface black, smooth and completely rhizine-free; lobe tips turned up and split from beneath to release a lip-shaped mass of granular soredia. That combination is Hooded Tube Lichen.