According to the Federal government's web site, invasivespecies.gov: One study estimates that the total costs of invasive species in the United States amount to more than $100 billion each year. (Pimentel et al., 1999).  Invasive species impact nearly half of the species currently listed as Threatened or Endangered under the U.S. Federal Endangered Species Act. One invasive plant, purple loosestrife, can produce up to 2.7 million seeds per plant yearly and spreads across approximately 1 million additional acres of wetlands each year.   For More Information:  Parade Magazine Cover Story Alternatives to Invasive Plants in Connecticut Sources of Native Plants:  Perennials The Nature Conservancy:  Abating the Threat of Invasive Species IPANE:  UCONN's Information on Invasive Species