Plant leaves rarely play a major role in reproduction. In this study, we report a phenomenon in which overlapping leaves enclose flowers and fruits possibly to protect against cold. Schizopepon bryoniifolius (Cucurbitaceae) is an androdioecious scandent annual commonly inhabits the edge of deciduous forests on the foot of mountains in Japan. From late August to September, males form conspicuous racemose or paniculate inflorescences with many flowers, while hermaphrodites produce small solitary flowers in the axils of leaves. Early in the flowering season, hermaphrodite flowers are spatially separated from each other due to long internodes. In contrast, later flowers are packed together on a dwarf shoot with very short internodes. Very late in the flowering season leaves grow to enclose these flowers and fruits. We found that enclosing leaves were larger in colder sites at higher altitudes. Under solar radiation, temperature inside an enclosure was up to 4.6°C higher than ambient temperature. Besides, removal of enclosing leaves negatively affected fruit growth. On the other hand, enclosure may have an adverse effect on outcrossing. The negative correlation between the male ratios and altitude reported in a previous study may be related with higher proportions of selfing enclosed flowers at cooler sites.