Typha species are increasingly considered invasive weeds in wetlands of eastern North America. Typha angustifolia and T. x glauca are often seen as more invasive than T. latifolia, but there are few comparative biogeographic data on these three species. We examined 1,127 Typha specimens archived in major herbaria to map changes in the distributions of these species since the late-19th century. We also analyzed pollen records from the North American Pollen Database (NAPD) to examine longer-term trends in abundance of each Typha species. Proportion curves comparing the relative spread of T. angustifolia and T. latifolia reveal a period of enhanced range increase in T. angustifolia in the early to mid-20th century. From the mid-20th century onwards, the two species increased at the same rate. The relatively higher rate of spread in T. angustifolia levels off after 1930 in the more coastal region of New England, but does not stop increasing inland and in more northern regions such as Ontario until after 1970. Pollen data suggest that 80% of relevant sites in the North American Pollen Database showed an increase in the abundance of one or both Typha species over the past 1,000 years. However, there was no significantly greater increase in one type of pollen compared to the other. Typha-type pollen grains in the form of tetrads and monads are recorded in the database throughout the Holocene and late Pleistocene; however, few studies analyzed the morphology of the pollen grains sufficiently to allow for positive identification of T. angustifolia. In the few recent records that made those measurements, small numbers of pre-settlement incidences of T. angustifolia and T. x glauca are recorded. Pollen and herbarium data suggest that T. angustifolia may have been present in North America prior to European settlement, but was not widespread. Herbarium data confirm that the range increase has been considerably larger in T. angustifolia than in T. latifolia since 1880, but both Typha species have been increasing at the same rate for the past several decades, and both will continue to display invasive tendencies in disturbed wetlands.
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Vol. 28 • No. 1