There is a particular pleasure in kneeling beside a tarn, hand lens in one hand, a slim field guide in the other, trying to put a name to the fuzzy green cushions and crusty grey patches that cling to the rocks and peat. The Lake District's tarns—those jewel-like pools cupped in the fells—are wonderful places to learn your mosses and lichens. They grow together, often side by side, and telling them apart is easier than you might think once you know what to look for.

Why Tarns Are a Haven for Mosses and Lichens

Tarns are rarely just water. Around every tarn there is a mosaic of microhabitats: submerged stones, splashed rocks at the water's edge, damp peat hags, dry boulders on the surrounding fell, and the occasional stunted tree or shrub. This variety, combined with clean air and high rainfall, makes the Lake District a stronghold for bryophytes (mosses and liverworts) and lichens. Many species here are adapted to extremes: they can dry out completely and then revive within minutes when rain returns. That resilience means you can find them almost any time of year, though they look their best after a spell of damp weather.

The Basic Difference: Mosses Versus Lichens

Before you worry about species, get the group right. Mosses are small plants with stems and leaves, however tiny. They are usually green, though some turn red, brown or golden. They have a soft, spongy or feathery feel and often grow in cushions or wefts. Lichens are not plants at all; they are a partnership between a fungus and an alga or cyanobacterium. They come in crusty, leafy or shrubby forms, and their colours range from grey and green to vivid yellow and orange. A hand lens reveals the difference quickly: moss leaves have a distinct midrib and cells, while lichens show a continuous thallus or tiny fruiting bodies.

Reading Colour and Texture

Colour is your first clue. On tarn edges, look for the deep crimson of Sphagnum mosses in boggy hollows, or the golden-green of a Polytrichum commune cushion. Racomitrium lanuginosum, a common moss on exposed rocks, is grey-green when dry but turns blackish-green when wet. Lichens are often more muted: the grey-green rosettes of Parmelia saxatilis on rocks, the bright yellow of Xanthoria parietina on nutrient-rich stone (often where birds perch), or the pale grey cups of Cladonia pyxidata on peat. Texture matters too. Mosses feel soft and yielding; lichens feel crusty, brittle, or rubbery. Some lichens, like Peltigera, are leafy and look like moss until you notice they have no stems or leaves.

Growing Position: Where to Look

Position is a powerful filter. Mosses dominate the wet zones: submerged in the tarn, in the splash zone, and on damp peat. Look for Sphagnum floating at the edges, Warnstorfia fluitans in shallow water, and Andreaea on wet rocks. Lichens prefer drier, more exposed surfaces. On the dry boulders around a tarn, you will find crustose lichens (like Rhizocarpon) and foliose lichens (like Umbilicaria). On peat, Cladonia species are common. A simple rule: if it is wet and soft, think moss; if it is dry and crusty, think lichen. But there are exceptions—some mosses grow on dry rocks, and some lichens thrive in damp shade.

Using a Hand Lens and a Simple Field Guide

A 10x or 20x hand lens is the single best tool. For mosses, look at the leaf shape, whether the leaves are straight or curved, and whether there is a nerve (midrib). Check for capsules—the little spore-bearing cases on stalks. For lichens, look at the thallus: is it crusty, leafy or shrubby? Are there apothecia (fruiting bodies) that look like tiny cups or discs? A simple field guide with photographs and keys will help you narrow down your finds. Start with common species and don't try to identify everything at once. The more you look, the more you will notice. And remember: a tarn is a fragile habitat. Keep your feet out of the water where possible, and never pick mosses or lichens from rocks—photograph them instead.

• For mosses: leaf shape, midrib, capsule, growth form (cushion, weft, mat).
• For lichens: thallus type (crusty, leafy, shrubby), colour, apothecia, presence of soredia or isidia.
• For both: habitat, substrate (rock, peat, wood), and moisture level.