Root Rot Heterobasidion annosum (Fr.) Bref. (illustrated (c) 25% life size) Fruit body variable in shape, frequently forming large, resupinate patches or irregular knobbly brackets 5–30cm×3–15cm across, 1–2cm thick, margin thin, acute; upper surface covered in a light brown crust, darkening with age, margin white; uneven and lumpy. Flesh whitish to pale wood-coloured; smell strongly fungusy. Tubes 2–5mm long in each annual layer. Pores 2–4 per mm, varying from circular to angular or irregularly elongated; white, browning with age. Spores 4.5–6×3.5–4.5¼, ovate; white. Hyphal structure dimitic; generative hyphae without clamp connections. Habitat parasitic on roots of coniferous trees, causing intensive rot and ultimately death of the infected tree; occasionally also infecting deciduous trees; all year, perennial. Very common, causing serious economic losses of conifers. Not edible. Note recent evidence suggests that this is probably a species complex.