Premise: Heterospecific pollen transfer, the transfer of pollen between species, is common among co-flowering plants, yet the amount of pollen received is extremely variable among species. Intraspecific variation in heterospecific pollen receipt can be even greater, but we lack an understanding of its causes and fitness consequences in wild populations. Methods: We examined potential drivers of variation in heterospecific pollen receipt in Oenothera fruticosa. We evaluated the relationship between heterospecific and conspecific pollen receipt and considered how visitation by different pollinator groups, local floral neighborhood composition, and flowering phenology affect the total amount and proportion of heterospecific pollen received. Finally, we tested whether variation in heterospecific pollen receipt translated into lower seed production. Results: Heterospecific pollen was ubiquitous on O. fruticosa stigmas, but the amount received was highly variable and unrelated to conspecific pollen receipt. Heterospecific pollen receipt depended on pollinator type, the proportion of nearby conspecific flowers, and flowering date. Significant interactions revealed that the effects of pollinator type and neighborhood were not independent, further contributing to variation in heterospecific pollen. Naturally occurring levels of heterospecific pollen were sufficient to negatively impact seed set, but large amounts of conspecific pollen counteracted this detrimental effect. Conclusions: Although selection could act on floral traits that attract quality pollinators and promote synchronous flowering in O. fruticosa, the risk of heterospecific pollen is equally dependent on local floral context. This work highlights how extrinsic and intrinsic factors contribute to intraspecific variation in heterospecific pollen receipt in wild plants, with significant fitness consequences. K E Y W O R D Sco-flowering, floral neighborhood, flowering phenology, interspecific pollen transfer, intraspecific variation, Onagraceae, pollen load, pollination, pollinator effectiveness, seed set Over 80% of angiosperms rely on animal pollinators for successful pollination (Ollerton et al., 2011). Yet because most plants share pollinators with several to a few dozen other co-flowering species (Jordano, 1987;Waser et al., 1996), this success can be compromised by pollinator-mediated competition among plant species (Brown et al., 2002;Lopezaraiza-Mikel et al., 2007). Plants can compete directly for visitation by shared pollinators (Waser, 1978) or indirectly when shared pollinators transfer pollen between plant species, termed heterospecific pollen transfer (HPT; Morales and Traveset, 2008). Heterospecific pollen transfer is extremely common in co-flowering communities, and its incidence and intensity vary markedly across species (McLernon et al., 1996;Fang and Huang, 2013;Tur et al., 2016), with implications for the evolution of floral morphology, species divergence, and community structure (Moreira-Hernández and Muchhala, 2019). Even as our understandi...