Arisaema: Pollination by lethal attraction

Abstract

Female individuals in the genus Arisaema are the only plants known to imprison their pollinators permanently. Their lethal pollination system has long attracted the interest of evolutionary biologists and naturalists. Nonetheless, the mechanisms of how Arisaema plants lure their victims to the brink of death are only just being unveiled. Here, I briefly review the unique reproductive biology of these plants, focusing on the possibility of sexual deception to lure pollinating victims, and its role in the evolution of new species.

Back from the dead: A fungus gnat pollinator turns Arisaema lethal trap into nursery

“…Arisaema thunbergii is commonly found in the dark, shaded understory of evergreen broad-leaved forests in western Japan (Murata et al, 2018). Similar to other Arisaema species, A. thunbergii employs a pollination system that effectively traps pollinators within the female spathe (Figure S1) (Suetsugu, 2022;Vogel & Martens, 2000). The sterile appendix of A. thunbergii is characterized by its thick, stout base that gradually tapers above the helmet, forming a flaccid thread that curves downward, resembling a fishing rod (Takasu, 1987).…”

“…Arisaema (Araceae), a genus comprising approximately 200 species, is renowned for its unique pollination system that permanently ensnares pollinators, primarily fungus gnats belonging to the family Mycetophilidae and Sciaridae (Matsumoto et al, 2021; Suetsugu, 2022; Suetsugu et al, 2021; Vogel & Martens, 2000). Historically, mushroom mimicry, or brood‐site mimicry, has been perceived as the main pollination strategy for Arisaema , because the majority of species are pollinated by fungus gnats that are typically mycophagous during their larval stages (Vogel & Martens, 2000).…”

“…Historically, mushroom mimicry, or brood‐site mimicry, has been perceived as the main pollination strategy for Arisaema , because the majority of species are pollinated by fungus gnats that are typically mycophagous during their larval stages (Vogel & Martens, 2000). Yet the lack of mushroom‐like scents and structures in many Arisaema species has challenged the prevalence of this strategy (Suetsugu, 2022; Suetsugu et al, 2021). Suetsugu et al (2021) suggested that sexual deception could be more widespread, especially because some Arisaema species predominantly attract male fungus gnats, which may indicate the emission of pheromones that mimic female gnats.…”

Thread‐like appendix on Arisaema urashima (Araceae) attracts fungus gnat pollinators

“…The genus Arisaema possesses a lethal pollination mechanism, in which they permanently trap pollinators (mainly Mycetophilidae and Sciaridae) in the female spathes (Appendix S1: Figure S1). The appendix often plays a vital role in pollinator attraction, even when it is inconspicuous and hidden by the spathe, because the olfactory cues emitted by the appendix are the basis for the attraction (Suetsugu, 2022; Suetsugu et al, 2021). In A. urashima , the appendix is thread‐like, 40–60 cm long, and protruding, with the upper half bent abruptly downward; it gradually thickens toward the base, transitioning into the floriferous part of the plant (Appendix S1: Figure S1).…”

Post‐pollination barriers contribute to coexistence of partially pollinator‐sharing Arisaema species (Araceae)

“…Thus, subsequent studies treated post-pollination isolation as weak or absent among these species (Matsumoto et al, 2019;Suetsugu, 2022;Suetsugu et al, 2021). However, since the mechanism of post-pollination isolation at other stages has not been studied, we do not know whether there are strong post-pollination barriers among Arisaema species.…”