Gilled Polypore

The Gilled Polypore (Trametes betulina, long known as Lenzites betulina) is the classic example of a polypore that has abandoned round pores in favour of blade-like plates. Viewed from above it is an ordinary tough turkey-tail-like bracket: thin, leathery, concentrically zoned and covered in fine hairs. Turned over, it reveals a hymenophore of thick, radiating, gill-like ridges — a structure that has evolved independently from the true gills of agarics.

This apparently agaric-like underside caused the species to be placed for a long time in its own genus Lenzites, but molecular work has shown it sits squarely inside Trametes alongside the turkey tail and its allies, in the Polyporaceae. The gill-like plates are simply an elongated, unbroken form of the pore layer; they are thick, tough and non-waxy, quite unlike the thin, soft, knife-edged gills of an agaric.

Because the fruitbodies are perennial in effect — tough, weather-resistant and persisting for a year or more — the species can be found in any month. Fresh growth in autumn shows white to cream plate edges and a well-defined zoned cap, while old brackets weather grey and are frequently greened by algae growing on the hairy upper surface.

Cap

The bracket is 2–10 cm across and only a few millimetres thick, semicircular, fan-shaped or shelf-like, attached broadly to the wood without a stalk, and often fused laterally with neighbours into long compound rows. The upper surface is dry, densely finely hairy or velvety, and marked with concentric zones in cream, buff, tan, grey-brown and rust, the outer zone usually palest; old specimens weather grey and are often tinted green by algae.

Gills / pores

The underside consists of thick, radiating, gill-like plates 1–4 mm apart, cream to pale buff, sometimes forking or interconnected by cross-walls near the base and occasionally breaking down into elongated maze-like pores toward the point of attachment. The plates are tough, blunt-edged and continuous with the cap flesh — they cannot be peeled away as a separate layer, and they do not have the thin sharp edges of true agaric gills.

Stipe

Absent. Attachment is directly and broadly to the wood.

Flesh & spore print

The flesh is thin, white to cream, tough and leathery, unchanging when cut, and remains flexible when moist but hardens when dry. There is a distinct thin layer of flesh between the hairy upper surface and the plates. The spore print is white, though it is rarely taken; spores are small, smooth, cylindrical and inamyloid.

Trametes betulina grows on dead hardwood — logs, stumps, standing dead trunks, fallen branches and cut ends — with a strong preference for birch, as its epithet indicates, but it is also frequent on beech, oak, alder, willow, poplar, cherry and many other broadleaves, and it occasionally appears on conifers. Brackets typically form dense overlapping tiers or long fused ranks along the flanks of a log or across a cut stump face.

The fruitbodies persist through the year, so the species can be recorded in any season, with fresh growth flushes commonly in late summer and autumn. It is widespread across the north temperate zone in Europe, Asia and North America, and is common in woodland, hedgerows, parks and anywhere birch or other hardwood debris is left standing.

The Gilled Polypore is a saprotroph that causes a white rot, secreting enzymes that break down lignin as well as cellulose so that the decayed wood becomes pale, soft, fibrous and eventually stringy. It is an effective coloniser of dead standing stems and freshly fallen logs, particularly of birch, and it competes for territory with other bracket fungi such as turkey tail, with which it frequently shares a single log.

The gill-like hymenophore represents an increase in spore-bearing surface area per unit of tissue compared with a flat surface, achieved without the maze of walls needed to build round pores. Because the brackets are tough and weather-resistant, spore release can be spread over a long period and resumed whenever conditions are suitable, rather than concentrated in one brief flush. In doing so the species contributes steadily to the recycling of hardwood carbon and nutrients in temperate forests.

Trametes versicolor, the turkey tail, shares the thin, zoned, hairy bracket form and often grows on the same log, but its underside is a layer of fine round white pores rather than radiating plates. Trametes hirsuta and T. pubescens likewise have pored undersides and paler, shaggier caps.

Daedaleopsis confragosa and Daedalea quercina have maze-like or elongated slot-shaped hymenophores that can approach the plate structure of this species, but their brackets are much thicker and woodier, their flesh is often brown rather than white, and their labyrinths are irregular rather than cleanly radiating; Daedaleopsis also bruises reddish. Gloeophyllum sepiarium has genuinely gill-like plates too but is rusty brown to orange-brown with darker zoning, grows chiefly on conifer wood and worked timber, and has brown flesh. True agarics such as Panellus or Crepidotus differ in having thin, soft, sharp-edged gills, fleshy rather than leathery tissue, and no zoned hairy upper crust.