Japanese and giant knotweed seed reproductive ecology

Abstract

Japanese knotweed (Polygonum cuspidatum Sieb and Zucc.) and Giant knotweed (Polygonum sachalinensis F. Schmidt ex Maxim) are invasive, exotic perennials. They were introduced from eastern Asia as ornamental plants. These species were found throughout Pennsylvania especially along riparian, roadway, and railway corridors, and in waste areas. Japanese and Giant knotweed propagate asexually by rhizomes and basal buds. Researchers in the United Kingdom reported no viable seed set on Japanese knotweed due to the absence of male-fertile plants. In New Jersey, seedlings were found under Japanese knotweed. This research project was conducted to determine if the prolific seed produced within Pennsylvania was viable and capable of germinating in nature. The reproductive ecology of Japanese and Giant knotweed seed was studied in eighteen populations from three river drainages across Pennsylvania. Field investigations showed that Japanese and Giant knotweed plants produce millions of seed annually. Two-year-old seedlings were discovered at four study sites in 1997 and 1998. Apparent viability assessments of seeds were made using seed coat and endosperm conditions. Seed coat was not a consistently good indicator of seed viability. Germination requirements were determined by testing the effects of moisture, temperature, and wing treatments on four seed sources over 30, 75, and 120 day storage periods. The temperature and moisture treatment combinations were all sufficient for germination. The overall mean germination rates were above 84 percent. Significantly different results were achieved with cold (3 degrees Celsius) moist conditions, yielding 95 percent mean germination over all storage times. Seedbank studies were conducted to determine the existence of naturally occurring knotweed seedbeds at four sites. The range of seedlings per soil core was 0-120. This equates to greater than 5,000 potential seedlings per square meter at the Rothrock and Lumber Road sites. Japanese and Giant knotweed were capable of reproducing sexually in these experiments.

Parent Publication

• 12th Central Hardwood Forest Conference

Citation

Niewinski, Amy T.; Bowersox, T.W.; McCormick, L. H. 1999. Japanese and giant knotweed seed reproductive ecology. In: Stringer, Jeffrey W.; Loftis, David L., eds. 1999. Proceedings, 12th central hardwood forest conference; 1999 February 28-March 1-2; Lexington, KY. Gen. Tech. Rep. SRS-24. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southern Research Station. 293 p