Population Status of a Regionally Endangered Plant, <i>Lunaria rediviva</i> (Brassicaceae), near the Eastern Border of Its Range

Long-term studies of plant populations provide valuable knowledge on the influence of various environmental factors on plant species. The status of edge-range species populations is especially important to be studied due to their higher vulnerability to extinction. This paper aimed to study the <i>Lunaria rediviva</i> population at the eastern border of its range (National Park “Smolny”, Republic of Mordovia, Russia). The study was carried out in 2013–2018. Assessment of the <i>L. rediviva</i> population was performed on the basis of individual parameters of plants (height of the individual, number of leaves per individual, number of inflorescences, flowers, fruits per one generative individual, and the fruit set), and density of individuals. Ontogenetic structure of the population was identified by distinguishing juvenile, mature vegetative, and reproductive individuals. The relationships between weather conditions (mean values of temperature, air moisture, wind strength, precipitation divided to three decades per month) and population parameters of <i>L. rediviva</i> were identified. Results showed changes in the ontogenetic structure of the population. The type of its population changed from vegetatively oriented to bimodal, with a decrease (R² = 0.686) in the proportion of mature vegetative individuals. We demonstrated a significant decline in some parameters of the <i>L. rediviva</i> reproduction. We found a significant negative correlation between the fruit set and the moisture at mid-July (r = −0.84, <i>p</i> < 0.05), and wind strength in late May (r = −0.83, <i>p</i> < 0.05) and early June (r = −0.83, <i>p</i> < 0.05). It was found that the number of both flowers and fruits per individual is significantly positively correlated with the precipitation in late April, and they negatively correlated with these parameters and the temperature in late July. We assume that the habitat shading negatively influences the <i>L. rediviva</i> population status.