Pollen dispersal regulates the formation of the invasive, wind-pollinated hybrid cattail T. × glauca, the F1 offspring of the broadleaf (T. latifolia) and narrowleaf (T. angustifolia cattail. An earlier study suggested that pollen dispersal by T. latifolia might be spatially restricted, with most dispersal occurring over distances less than 2 m. Restricted pollen dispersal would imply that hybrid formation primarily occurs within mixed stands of cattails. Hybrid formation might also be affected by preferential receipt of conspecific pollen, but this has not been investigated for cattails. We compared patterns of pollen dispersal for T. latifolia and T. angustifolia using a wind tunnel. We then tested whether patterns of pollen receipt were biased toward the capture of conspecific versus heterospecific pollen using monospecific cattail stands with a single local pollen source. Results from the wind tunnel partially supported the previous finding of spatially restricted pollen dispersal for T. latifolia, the paternal parent of F1 hybrids. Pollen receipt by T. angustifolia was biased toward the capture of conspecific pollen. Localized pollen dispersal by T. latifolia and preferential conspecific pollen capture by T. angustifolia should reduce rates of hybrid formation below that expected under random mating.

Pollen dispersal was assessed in a wind tunnel. Inflorescences of each of Typha latifolia and T. angustifolia were inserted into a wind tunnel and tapped by a paddle to release pollen. Pollen was captured downwind on microscope slides covered in petroleum jelly at distances of 0.2, 0.4, 0.8, 1.6, 2.0, 3.0, 4.0, and 5.0 m from the inflorescence and positioned at approximately the height of the centre of the pollen source. Dispersal was assessed at each of three wind speeds: 1 m/s, 2 m/s, and 5 m/s. We conducted three trials for each Typha species at 1 m/s and 5 m/s and two trials for each species at 2 m/s. The number of pollen grains (tetrads for T. latifolia and monads for T. angustifolia) in 1 cm² was counted manually under a microscope. Data presented are counts of pollen grains for each distance x species combination for each trial conducted. 

Pollen capture of T. latifolia and T. angustifolia was assessed in each of two cattail stands (sites) near Peterborough, Ontario. At one site (Cavan), T. latifolia was the only cattail species present, and at the other (Uxbridge), T. angustifolia was the only cattail species present. Cattails at each site were emasculated before they shed pollen and the female portion of the inflorscence bagged to ensure recipient plants did not receive pollen from other plants at the sites. One each of two trials days at each site, donor cattails (one of each of T. latifolia and T. angustifolia) were put in place to act as pollen sources for four hours. These donor plants had been collected from nearly and put in pots to be left in the middle of the sites to act as pollen sources. A subset of female inflorescences were unbagged once the donor plants were in place and pollen was left to disperse naturally from the donor plants. After four hours, stigmas were removed from the unbagged recipient plants and immediately stained and mounted on microscope slides using basic fuschin jelly. Pollen grains of each species within 1 cm² were counted manually under a microscope. These counts were scaled by the area of the slide covered by stigmas. Counts were converted into proportion of grains being T. latifolia for data analysis. 

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