Abstract
The Javanese long pepper, Piper retrofractum, has been used as a traditional spice and medicinal plant in the Yaeyama region of Okinawa Prefecture, the westernmost territory of Japan. We examined geographic distribution of P. retrofractum and characteristics of its habitat in Okinawa Prefecture. A broad distribution range of P. retrofractum was confirmed, while the frequency of occurrence varied geographically; i.e., this plant was frequently observed in the southwestern area (Sakishima Islands including Yaeyama region), less frequently found in the northern area (Okinawa Islands), and not found on the eastern area (Daitou Islands). Although P. retrofractum has been regarded as dioecious, plants bearing male spikes were not found in the field, and all plants sampled and grown by cutting bore only female spikes, suggesting male plants do not occur in Okinawa Prefecture. Occurrence of P. retrofractum was restricted almost exclusively to environments developed by humans such as residential areas and farmland; this plant was rarely found in natural vegetation such as forest edges. Vines of P. retrofractum frequently attached to substrates of concrete, mortar, limestone, wood, and trees; other substrates such as metal and synthetic resin were uncommon. When plants were grown for sexing in a glasshouse, infestations of the spider mite Tetranychus okinawanus and unidentified mealybugs repeatedly occurred, suggesting these are potential pests in P. retrofractum cultivation. All of the newly obtained knowledge of P. retrofractum will be useful for future studies on cultivation and cultivar selection of this plant.
