Pollination Ecology of Impatiens sirindhorniae (Balsaminaceae), an endemic species from southern Thailand ​

Impatiens sirindhorniae Suksathan & Triboun is an endemic balsam restricted to peninsular Thailand. It is currently threatened by severe habitat destruction and fragmentation, which may reduce reproductive success in pollinator-dependent plants. To clarify its breeding system and pollinators, we conducted controlled pollination experiments, field observations of floral visitors, and measured flower traits associated with pollination syndrome. The absence of fruit set under spontaneous self-pollination indicates that I. sirindhorniae relies on animal pollinators for pollination. Although fruit set did not differ significantly between hand-self- and hand-cross-pollination treatments, seed number per fruit was significantly lower in hand self-pollinated flowers, suggesting partial self-sterility. Seven insect visitor species were recorded, including four lepidopterans and three ant taxa. Ant visitors were excluded as potential pollinators because stigma contact was not observed. Among lepidopteran visitors, Notocrypta curvifascia (Hesperiidae) visited both male-and female-phase flowers, making contact with stamens and stigmas with its proboscis, and pollen grains of I. sirindhorniae were observed on the captured individual. The behavioral patterns and morphological fit of this butterfly suggest that this species is the primary pollinator of I. sirindhorniae. Given its dependence on lepidopteran pollinators and partial self-sterility, conservation of this endemic species should focus on maintaining pollinator habitats and enhancing connectivity among remnant populations to facilitate cross-pollination and sustain genetic diversity.