Reproductive aspects and pollination biology in endoparasitic Pilostyles thurberi (Apodanthaceae)

Abstract

Biotic pollination is typically a mutualism between plants and their pollinators, where each partner receives a benefit. However, plants can resort to various reproductive strategies to attract pollinators. Within angiosperms, a group of plants known as endoparasites is comprised of only flowers or inflorescences. These plants exhibit various reproductive strategies, such as different sexual systems and attractants, and most are dependent on animals for pollination. In the endoparasitic plants of the family Apodanthaceae, unisexual flowers are predominant, resulting in dependence on pollinators. Pilostyles thurberi is characterized by small flowers, but limited information exists about its reproductive strategies. This study investigated various reproductive aspects of P. thurberi. We described and compared its hosts, sexual flower arrangement, floral concentration, rewards, and reproductive success in different populations. Furthermore, we determined whether the floral display operates as an attractant by monitoring pollinators for two years. Our results revealed that P. thurberi has unisexual flowers with male, female, and mixed sex arrangements. Bees and wasps are the effective pollinators and are attracted by the floral display independently of flower sex. This study was the first to record the production of small amounts of crystallized nectar by the nectary disk of both floral sexes. Moreover, the findings were compared with those of other endoparasitic plants, such as Cytinaceae, Mitrastemonaceae, Rafflesiaceae, and other Apodanthaceae. It is necessary to continue studying the plant–pollinator interactions and reproductive strategies of parasitic plants such as Apodanthaceae, since not much evidence on how they reproduce and survive in the wild exists.