Microscopic reproductive characters enable discrimination of cattail taxa in a highly admixed hybrid zone.

Understanding and managing invasive taxa requires accurate identification, which can be challenging when the invader is an interspecific hybrid. An example of this is the hybrid cattail Typha × glauca, which is found in a widespread and expanding hybrid zone in North America along with its parent species Typha latifolia and Typha angustifolia. In some regions, this hybrid is considered invasive because it dominates wetlands, reduces biodiversity, and alters ecosystem functioning. It is also a complex hybrid zone that includes advanced-generation hybrids and hybrid backcrosses to both parent species (hereafter collectively referred to as non-F1 hybrids). Previous studies have shown that gross morphological characters of non-F1 hybrids overlap with those of their parent species, and this can hinder identification and hence monitoring and management programmes in areas of high non-F1 abundance. Here, we show that microscopic pollen and bracteole characteristics are overall highly reliable for taxonomic identification, as they agreed with the genotype-based taxonomic assignments for 409/426 (96%) and 232/244 (95%) of plants, respectively, with non-F1 hybrids the most common source of error. Although these characteristics are limited to flowering plants, and in the case of pollen to a relatively short period of time, they are relatively easy to apply; however, the abundance of T. latifolia may be underestimated if plants are identified from inflorescence traits. Nevertheless, this low-cost method for distinguishing cattail taxa could facilitate research into this expanding hybrid zone, plus targeted management of hybrid cattails in areas where they dominate wetlands and disrupt ecosystems.