An invasive plant may overcome pollination specialisation with a versatile breeding system

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Abstract Plants with specialised pollination syndromes are less likely to become invasive compared to those with generalist syndromes, yet some highly invasive species have specialised syndromes. Few empirical studies have investigated the reproductive biology of invasive plants with specialised pollination syndromes, preventing a deep understanding of this apparent contradiction. Senna species (Fabaceae) exhibit the specialised buzz-pollination syndrome, and several Senna species are invasive globally. We assessed whether Senna obtusifolia could reproduce uniparentally via autonomous selfing, vector-mediated selfing, or without pollen (apomixis). We assessed whether it was pollen limited in either the studied native (Mexico) or invaded (Australia) regions. We experimentally manipulated pollinator access and pollen deposition in both regions and found that up to 40% of flowers set fruit from self-pollination and up to 24% of flowers set fruit in the absence of pollen. We found no evidence that S. obtusifolia was pollen limited in either region, suggesting that it has attracted suitable pollinators in both studied regions. Our findings suggest that S. obtusifolia has a mixed breeding system, combining selfing, apomixis, and outcrossing. This versatile breeding system may be key to its invasiveness, enabling uniparental reproduction during the early stage of colonization, while maintaining genetic diversity through outcrossing.

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