The Habitat of the Neglected Independent Protonemal Stage of Buxbaumia viridis

Buxbaumia viridis is a well-known species of decaying deadwood, which is protected in Europe. All previous studies dealing with the ecology of B. viridis rely on the sporophyte generation because the gametophyte generation is allegedly undetectable. Recent advances have shown that the protonemal stage, including gemmae, is recognizable in the field, thereby considerably modifying our perception of the species' range and habitat. In France, we demonstrate the existence of independent protonemal populations, with the implication that the range of B. viridis is widely underestimated. Sporophytes and sterile protonema do not share the same ecological requirements. The sporophyte stage was found in montane zones, almost exclusively in coniferous forests, and on well-decayed wood. The sterile protonemal stage extends to lower elevations, in broad-leaved forests, and on wood in a less advanced state of decay. Our results suggest that the humidity could be one of the most relevant explanatory variables for the occurrence of sporophytes. Opening of the canopy seems to promote sporophyte development. Previous anomalous observations of B. viridis growing on humus or bark might be explained by the presence of a protonemal population that is able to produce sporophytes under rarely occurring but favorable climatic events.