Heterosis in invasive F1 cattail hybrids (Typha × glauca)

• Invasive hybrid cattails (Typha × glauca) dominate wetlands around the Great Lakes.
• We compared heights of hybrids to parental species throughout the growing season.
• Typha latifolia had the earliest start, but its height advantage was short-lived.
• F1 hybrids were taller than parentals or backcrosses for most of growing season.
• Heterosis in the form of superior height helps T. × glauca to dominate sites.

Rapid evolution following interspecific hybridization can facilitate biological invasions. Around the Great Lakes in North America, the hybrid cattail Typha × glauca is dominating wetlands and displacing both parental species. We measured water depth and height of T. × glauca and its parental species (Typha angustifolia and Typha latifolia) throughout the growing season at a site near Lake Ontario that harbors both parental species plus hybrids. We found no evidence of niche partitioning by water depth, nor was there evidence that water depth was influencing plant height. At the beginning of the growing season, T. latifolia comprised the tallest plants, but this potential advantage was short-lived, and for most of the growing season, F1 hybrids were taller than all or most other taxa (T. angustifolia, T. latifolia, and advanced-generation/backcrossed hybrids). Heterosis, inferred from height, is therefore evident in F1 hybrids, but not in advanced-generation/backcrossed hybrids. Typha stands often achieve high densities, and the competitive advantage of superior height is likely contributing to the invasive success of T. × glauca F1 hybrids in the Great Lakes region.