Doctoral candidate Heather Briggs just published a chapter of her dissertation in the Annals of Botany, available for download at doi:10.1093/aob/mcv175.   The article what highlighted as a featured article in the journal!   Here is the blurb from Annals:

Most work on the impacts of heterospecific pollen deposition on plant fecundity has utilized hand-pollination experiments in greenhouse settings, and therefore we know little about the reproductive effects in the field. Briggs et al. (pp. 341–347) explored how patterns of naturally deposited heterospecific pollen relate to the reproductive output of Delphinium barbeyi. Heterospecific pollen deposition is common but at low levels across stigmas; there is a negative interaction between the effects of conspecific pollen and heterospecific pollen amount: the effect of conspecific pollen on viable seed production becomes weaker with greater heterospecific deposition on stigmas. Greenhouse hand-pollination studies and field studies should be tightly integrated in future to better understand how heterospecific pollen transfer can be detrimental for plant reproduction.

Briggs, H. M., L. M. Anderson, L. M. Atalla, A. M. Delva, E. K. Dobbs, and B. J. Brosi. 2016. Heterospecific pollen deposition in Delphinium barbeyi: linking stigmatic pollen loads to reproductive output in the field. Annals of Botany 117:341-347.