Where a bonfire has burned down to cold ash, or a heath fire has swept through and left the ground black, one of the first green things to creep back is often a moss. Within a season the scorched patch furs over with a soft yellow-green pile, then bristles all over with curved orange stalks. This is bonfire moss, Funaria hygrometrica, a plant that has made a living out of catastrophe and turns up wherever soil has been burnt, fed or freshly broken open.
The moss that follows fire
Funaria is a pioneer, quick to seize bare ground before slower plants arrive. Burnt sites suit it especially well, because a fire does two things it likes at once: it clears away every competitor and it leaves behind a dressing of ash. Wood ash runs alkaline and carries potash and other minerals, and that flush of nutrients across freshly cleared soil suits this moss almost perfectly. So it shows up on old bonfire patches in gardens and allotments, and across the blackened seat of a moorland or forest fire. Most mosses are slow perennials, content to creep along a wall or a log for decades; Funaria lives fast instead, fruiting heavily within a year or two and then fading once taller plants close back over the ground.
Recognising it
The tufts are low and rather loose, a fresh light green flushed with yellow, the short shoots carrying broad, concave, egg-shaped leaves bunched into a little bud at the tip. What truly catches the eye is the fruit. From spring the moss throws up long stalks, the seta, often a couple of centimetres tall and coloured a warm reddish-orange, each one bent over at the very top like a shepherd's crook or the neck of a swan. At that bend hangs the capsule, pear-shaped and slightly lopsided, grooved down its flank, green at first and ripening through amber to brown. On a well-fed colony these nodding stalks crowd so thickly that the whole patch reads more orange than green. Few common mosses fruit so freely or so showily, which makes one in capsule easier to put a name to than most.
A hygrometer on a stalk
The species name, hygrometrica, points to a real trick. The seta is keenly sensitive to moisture: as the air dries, it screws itself into a tight corkscrew, and as damp returns it slowly unwinds, the whole stalk twisting back and forth with every shift in the weather. The movement does real work: by turning and flexing, the stalk shakes the ripe capsule about and works its spores loose a few at a time, casting them off when the air is dry enough for them to drift. Around the capsule mouth sits a double ring of teeth, the peristome, the outer and inner sets joined at their tips into a delicate lattice that itself opens and shuts as humidity changes, metering out the spores by degrees rather than all in a rush. Under a hand lens it is among the prettiest pieces of machinery in the whole moss world, and a good reason to carry one, as how to identify moss sets out.
The textbook moss
Generations of botany students have met Funaria before any other moss. It is easy to find, easy to raise on a dish of damp soil, and it runs through the whole moss life cycle so plainly that it became the standard classroom example: the green thread, the protonema, growing from a germinating spore; the leafy shoots budding from that thread; the eggs and swimming sperm that need a film of water to meet; and the stalked capsule that rises only once they have. The looping, two-part life of every moss, the alternation of leafy plant and spore-bearing generation, shows here with unusual clarity, and its bones are laid out in what a moss actually is. Upright in tufts with its capsules borne at the shoot tips, Funaria is a tidy acrocarp, the habit weighed against the creeping carpet mosses in acrocarpous and pleurocarpous mosses.
In pots, paths and burnt corners
No fire is needed to meet it. Funaria ranks among the commonest weeds of plant pots, seed trays and greenhouse benches, arriving unasked on the clean, fed compost it finds so agreeable, and it settles just as readily on the rich soil of allotments and in the cracks of paving. Anyone who sows in pots will know the yellow-green film, and the little forest of orange stalks above it, that spreads over a tray left damp and undisturbed for a few weeks. It does no real harm and clears off by itself once conditions move on, though a crust thick enough to cap wet compost can be teased away before it seals the surface; the general line on unwanted moss is drawn in getting rid of moss. Out on its burnt patch, though, it repays a slow look before the grass grows back and shoulders it aside.