Overview
The Nail Fungus (Poronia punctata), also known charmingly as the dung button or nail-head mushroom, is a rare and ecologically distinctive coprophilous ascomycete fungus. Shaped remarkably like an antique wrought-iron nail or golf tee driven into a weathered dung heap, this small, striking fungus produces a flat, chalk-white circular disc speckled with tiny black dots. Once widespread across European pastures, it has vanished from most of its continental range, leaving the ancient New Forest of southern England as its primary global stronghold.
Biology and Physical Characteristics
Poronia punctata forms a tough, erect, stalked fruiting structure (stroma) measuring one to two centimeters tall. The base consists of a dark, velvety rooting stalk that anchors deep within the substrate, flaring upward into a disc-shaped or cupulate head five to fifteen millimeters across. The upper disc surface is smooth and alabaster-white to pale greyish-cream, peppered with numerous embedded black perithecia that resemble punctuation marks or miniature cloves. Each perithecium opens via a tiny ostiole pore that forcefully discharges large, dark brown, gelatinous-coated ascospores.
Behavior and Ecology
As an obligate coprotrophic specialist, Poronia punctata feeds exclusively on the fibrous, well-weathered dung of horses, ponies, and donkeys that feed on unfertilized native grasses and heathers. Spores ingested with pasture foliage survive mammalian digestive tract enzymes intact, germinating within expelled dung piles once primary bacterial fermentation subsides. In late autumn and mild winter months, the fungus produces stromata that project spores into the surrounding turf, ensuring new generations of grazing herbivores ingest the spores to complete the ecological cycle.
Conservation and Human Impact
Assessed as Vulnerable on the European Fungal Red List and categorized as a high-priority protected species in the UK, Poronia punctata has undergone dramatic historical declines throughout Europe. The widespread modernization of agriculture—particularly the transition from draft horses to tractors, intensive pasture improvement with chemical fertilizers, and the widespread veterinary use of chemical anthelmintics (such as ivermectin) that render horse dung toxic to fungal mycelia—has decimated populations. The preservation of traditional common grazing practices in the New Forest remains vital to preventing global extinction.
Interesting Factoid
Poronia punctata was once so common in Victorian England that country children called them ‘fairy nails,’ yet today it has vanished from almost all of mainland Europe, surviving almost exclusively where free-roaming ponies graze ancient commons free of modern worming drugs.
Last updated: October 2026