The sticky hemiparasitic plant Parentucellia viscosa catches hostplant seeds that may provision its descendants

Abstract

In addition to physiological functions, sticky plant trichomes perform a variety of anti-herbivory functions, such as deterring invertebrate and mammalian herbivores, and attracting the natural predators of stuck arthropods by providing them with immobilized prey. However, since the adaptive value of sticky glands has only been studied in a small fraction of trichrome-bearing plant species, other functions of these structures may yet be discovered. Several hemiparasitic plants, which obtain nutrients by both photosynthesis and from the roots of other plants, bear dense glandular trichomes on their aboveground parts. Field observations of the alien hemiparasitic plant Parentucellia viscosa were conducted in central Japan. The plants colonized a sparsely vegetated riverbank and gradually increased in number over time. The glandular trichomes on the plants not only entrapped small insects, but also grass seeds. It is thus possible that various sticky hemiparasitic plants, including P. viscosa, may intercept and capture the dispersed seeds of other plants, ensuring that their own seeds germinate in the same vicinity as those of the dispersing hostplant seeds in the following season. In so doing, P. viscosa may provision future juvenile plants with potential hosts. This scenario may be restricted to the early colonizing phase on plantless areas of disturbed soil. The seed-intercepting function of the glandular trichomes may act in conjunction with direct and indirect anti-herbivore defenses, and lower the dispersal of seeds of wind-borne plants in the vicinity beyond the reach of this hemiparasite.