Although fungal hyphae have few unique morphological features and most fungal structures are poor candidates for preservation over long periods of time as fossils, a respectable fossil record for fungi has been assembled in recent years. By far the most impressive fungi of the Ordovician/Devonian Period are specimens of the fossil genus Prototaxites, which were terrestrial organisms found from the mid Ordovician (460 million years ago) to the early Devonian, suggesting that they lasted a period of at least 40 million years (Boyce et al., 2007; Hueber, 2001). These fossils are among the ‘nematophyte phytodebris’ that constitutes the earliest evidence for terrestrial organisms. This ‘nematophyte phytodebris’ nomenclature was assigned in the middle of the nineteenth century and has no relevance to present-day understanding of taxonomy (that is, it does not necessarily indicate that the stuff was of plant origin); though it does indicate that confusion over the identification of the material is over 150 years old (see discussion in Hueber, 2001 and Taylor et al., 2010). Prototaxites specimens are generally large: over a metre wide (Wellman & Gray, 2000) and up to 8 m tall (Hueber, 2001) (Figs. 12.1 and 12.2; illustrated in colour in Moore et al., 2011, pp. 33–34). Prototaxites was also so common that it was a major component of these early terrestrial ecosystems, both in terms of abundance and diversity. Some of the earliest examples found were tree-like trunks constructed of interwoven tubes < 50 µm in diameter (concentrically arranged in transverse sections), and the fossils were interpreted to be small coniferous trees, though we now know that environments at the time Prototaxites was fossilised did not (yet) include large vascular plants.