Fungal dry rot. View of uplifted floorboards in a house, showing encrusting fungal growth on the wood. Dry rot is a decay of timber caused by the fungus Serpula lacrymans; infected wood shows a surface growth of white filaments, with leathery fruiting bodies producing rust-coloured spores. The brown and mustard colours seen here are typical. Dry rot is common in structural timbers in damp buildings with poor ventilation. The fungus ultimately reduces the wood to a dry and cracking brittle mass.