This account presents information on all aspects of the biology of Nervilia nipponica Makino (mukago-saishin) that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the International Biological Flora: distribution, habitat, communities, responses to biotic factors, responses to the environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, history, conservation and global heterogeneity.

Nervilia nipponica is a small, stoloniferous, seasonally dormant herb that grows in the understorey of evergreen forests in the humid subtropical zone of central and western Japan, with a few outlying populations on Jeju Island in South Korea. Its northern extent is defined by the 0ºC winter isotherm, and its occurrence is also limited by site aspect and incline. It is a weak competitor that occupies species-poor microsites in which bare ground and leaf litter predominate. Plant numbers tend to decline as percentage ground cover of surrounding understorey vegetation increases.

The inflorescence sprouts from a short-lived, subterranean tuber in late spring and leaf-flush occurs after fruit-set. However, most tubers do not flower in any one annual growth cycle. Long-term monitoring of individually marked plants suggests that tubers are resource-limited and that flowering constrains future genet growth. Nervilia nipponica is exclusively autogamous and has a strong capacity for vegetative propagation. The species is genetically depauperate but exhibits significant differentiation between populations, which comprise clonal clusters in phalanx formation.

The level of mycorrhizal infection differs between plant parts and through successive phenological stages. Stable isotope signatures indicate that the species is partially mycoheterotrophic, with fungal partners supporting growth particularly at lower light intensities. Despite this, falling light availability associated with forest succession can lead to population decline.

Populations tend to be small and prone to extirpation, but the species is probably under-recorded as a result of its ephemeral emergence above ground and inconspicuous habit. Management interventions likely to benefit the species at the site level include thinning dense forest canopy and removing encroaching ground cover.

Number of emergent plants of Nervilia nipponica was recorded in each of 27 quadrats in August 2004 and again in August 2007. The percentage ground cover of understorey vegetation up to height 2 m was estimated on both dates. The change in number of emergent plants over the study period was correlated to change in percentage ground cover.

All emergent plants occurring within a fixed plot measuring 10 x 14 m were marked and their locations were recorded as x and y coordinates to the nearest cm every year in late July to mid-August from 2003 to 2012. Observed and expected nearest neighbour distances were calculated and significance was measured using a Monte Carlo test in Point Pattern Analysis (PPA) software, which compares the complete distribution function of observed distances between nearest neighbours, F(di ≤ r), with the distribution function expected under a null hypothesis of complete spatial randomness, P(di ≤ r).

All emergent plants occurring within a fixed plot measuring 10 x 14 m were marked and monitored three times through each growing season (during the flowering, fruiting and leafing phases) for 10 years. Unmarked plants were labelled and incorporated into the record of the population’s demographic behaviour as they appeared. The pattern of emergence was inferred for each individual plant for the 10-year period.

Five plants were excavated from each of two populations (sites T1 and T2) in Tochigi Prefecture and their photosynthetic capacity was measured using a Li-6400 infrared gas exchange analyser (Li-Cor, Lincoln, Nebraska, USA). Net carbon assimilation rate (g glucose m-2 day-1) was calculated by aggregating the instantaneous net assimilation rate of the leaves (Anet, μmol CO2 m-2 s-1) and converting this to the mass of glucose (g mol-1) contributing to new biomass growth. Photosynthetic carbon gain calculated in this way was compared to measured carbon gain, as inferred from the difference in dry mass in cohorts of 4–5 plants harvested at monthly intervals (July, August, September and October) over three growing seasons (2014–2016). Each plant was divided into leaf and petiole, stolon and tubers, leaf area was measured, and all plant parts were oven-dried and weighed. Carbon gain dependency was defined as the ratio of calculated biomass gain from photosynthesis (derived from photosynthetic light-response curves using PAR data and the measured photosynthetic capacity of N. nipponica) to observed biomass gain (derived from mean dry mass differential from first to last sampling). Stable 13C and 15N isotope abundances were determined in N. nipponica and in a range of other co-occurring understorey herbs, including both chlorophyllous and achlorophyllous species at both sites in Tochigi Prefecture during July to September in 2014, to estimate the percentage carbon and nitrogen gain from fungal partners, following the methodology of Gebauer & Meyer (2003).

As explained in appended README file