The Least Moonwort (Botrychium simplex, Ophioglossaceae) in Germany

This paper provides a brief portrait of Botrychium simplex and starts by describing its biological characteristics and distribution in Germany. In the third part, a demographic study is presented reporting on long-term observations of the only presently known German population (Senne area, North Rhine-Westphalia). As with all moonworts, the spores of B. simplex germinate in the soil, and the gametophytes start developing only if they are infected by an arbuscular mycorrhizal symbiont. The sporophytes are mycotrophic as well. Sporophytes can remain dormant for one or more years without producing aboveground leaves. As a low growing plant and a weak competitor B. simplex is dependent on an open and low plant vegetation cover. The leaves are morphologically highly variable with the form of the sterile portion being particularly diversified. Of the several varieties distinguished in North America, var. tenebrosum occurs in Central Europe, in addition to the more common var. simplex. Botrychium simplex is a species inhabiting the north temperate to cool-temperate zone with a range that includes Europe, North America, India, and Japan. In Germany, localities from the past three centuries and 12 ordnance survey maps (German TK 25) are known. The majority of findings date back to the 19th century, only 5 have been reported for the 20th century. The dynamics of the population in the Senne area (North Rhine-Westphalia) were examined every year since 1994. At the time of its discovery (1993), the population appeared to be at an optimum stage and included three closely spaced sub-populations; in later years three more sub-populations were discovered. Only one sub-population produced leaves permanently (with the exception of one year). After just one year, a clear decrease in leaf number was registered, a trend that continued in subsequent years. Similar negative changes were found with regards to leaf length, the proportion of fertile leaves, and the number of sporangia formed per leaf The sporophyte is very short-lived in species of subgenus Botrychium, which includes B. simplex; the half-life is short as well and amounts to a few years only. The decrease in population size observed in the Senne agrees very well with the one predicted assuming a 3-year half-life. Additional factors, which could have been involved in the decline, various biotic factors and possible impairments, indirectly or directly caused by human activities are discussed as well. It is likely that, in addition to a spore bank, gametophytes, sporophytic juveniles or older rhizomes exist in the soil, which could contribute to leaf formation in the future. Therefore, long lasting conservation elements and management regimes are proposed for the population in the Senne to achieve the possibility of a rejuvenation of the population or a restoration of the population from the spore bank.