PS 11-120 - Two rare dwarf forms of the Asian, invasive plant Persicaria longiseta evidently evolved under lawn-mowing selection in the USA

Monday, August 7, 2017
Exhibit Hall, Oregon Convention Center
Edward M. Barrows, Biology, Georgetown University, Washington, DC

The Asian, annual, herbaceous plant Persicaria longiseta (Asiatic Waterpepper) is now a widespread alien, invasive species in Europe and North America. I found two previously unknown, very rare dwarf forms — a white-flowered one with narrow leaves and pink-flowered one with wide leaves — in a lawn and adjacent flower bed in Bethesda, Maryland in 2015. There were only about 15 plants of each form in their populations. In an attempt to understand their evolution, I tested hypothesis-1 that the plants’ dwarfism is genetically determined and hypothesis-2 that they produce seeds without animal pollination. To test hypothesis-1, I grew the dwarfs and the usual tall form from seeds in a common garden. To test hypothesis-2, I grew three plants of each dwarf form in a greenhouse without animal pollinators.


The two dwarf forms and taller form grew to their usual heights from seeds in their common garden (N = 10 of each kind). This indicates that their heights have a genetic basis. Both dwarf forms, grown without animal pollinators in a greenhouse, developed mature seeds, indicating that they produced seeds parthenogenetically, by intrafloral self-pollination, or both. Possible steps in the evolution of these dwarf forms include (1), lawn-mowing, browsing by Odocoileus virginianus (White-tailed Deer), or both selected for short plants that could produce seeds; and (2) the dwarf plants retained their dwarfism genetics in their tiny populations via selfing, parthenogenesis, or both. I did not see Odocoileus virginianus browsing on non-mowed, dwarf plants in the flower bed. A third known P. longiseta dwarf form occurs in Nara Park, Japan where it might have evolved under browsing pressure from Cervis nippon (Sitka Deer) (Suzuki, 2008).