Functional Significance of Thread‐Like Appendix on Arisaema urashima (Araceae) Attracting Fungus Gnat Pollinators

Abstract

Despite the longstanding speculation, the functional significance of the unique long, filiform appendices commonly seen in many fly-pollinated flowers remains unclear. In this study, we conducted a removal experiment of the thread-like appendix in Arisaema urashima to examine its functional significance. The present study provides strong evidence for the attraction role of the thread-like appendix targeting its primary pollinators, the Mycetophila fungus gnats. Our study elucidates a century-old conundrum in pollination ecology: the functional role of the long thread-like appendix in fungus gnat-pollinated flowers. Photo 1. The Japanese endemic flowering plant, Arisaema urashima, which possesses a spectacular thread-like sterile appendage, provided us with an opportunity to explore how the filiform structure affects pollination. Photo credit: Emiko Kato. Photo 2. Similar to many other Arisaema species, A. urashima traps fungus gnats to ensure pollination. In male inflorescences, the gnats accumulate increasing numbers of pollen grains (top right) while struggling to escape until finally locating and exiting through a small opening (left) at the base of the spathe. However, female morphs lack exit holes in their spathes. Therefore, the trapped gnats usually cannot escape until death (bottom right). Photo credit: Kenji Suetsugu. Photo 3. The lack of an exit hole on the female spathe increases the time spent by fungus gnats around the florets, resulting in more pollen deposition. Consequently, high fruit sets are often seen even in Arisaema urashima plants inflorescences with only one fungus gnat individual trapped. Photo credit: Eiji Ishitani. These photographs illustrate the article “Thread-like appendix on Arisaema urashima (Araceae) attracts fungus gnat pollinators” by Kenji Suetsugu, Hiroki Nishigaki, Shigeki Fukushima, Eiji Ishitani, Satoshi Kakishima, and Masahiro Sueyoshi published in Ecology. https://doi.org/10.1002/ecy.3782