Variation in sexual and clonal reproduction among introduced populations of flowering rush, Butomus umbellatus (Butomaceae)

Butomus umbellatus L. is an invasive emergent aquatic plant that exhibits w ide variation in seed production. Native European populations are fertile a nd diploid or sterile and triploid. However, adventive North American popul ations are widely reported to be sexually sterile. We quantified sexual fer tility and self-compatibility under greenhouse conditions for nine introduc ed populations from eastern Ontario, Canada. All populations were highly fe rtile and self-compatible. Each flower produced an average of 127 +/- 7 (me an +/- SE) filled seeds and 31.4 +/- 0.4% of seeds germinated. This level o f fertility is much higher than previously reported, even for fertile nativ e populations. We also quantified the production of seeds, flowers, and inf lorescence-borne asexual bulbils in 19 natural populations from eastern Ont ario; 17 populations were highly fertile (200 +/- 9 seeds/fruit) and 2 prod uced almost no seeds (0.0-0.3 seeds/fruit), because ovules were either not fertilized or were aborted soon after fertilization. We found no evidence o f a trade-off between sexual reproduction and clonal reproduction via bulbi ls. The wide variation in reproductive strategy observed in these populatio ns raises questions concerning the evolutionary loss of sex in clonal popul ations, and may have significant implications for the spread and management of this exotic species.