Ecological Risk Screening Summary - Duck Lettuce (Ottelia alismoides) - Uncertain Risk

Species that are considered uncertain risk need a more in-depth assessment beyond the Risk Summary to better define the species’ risk to U.S. environments.

Ottelia alismoides, Duck Lettuce, is a submergent aquatic plant that is native to freshwaters in southern and eastern Asia and Australia. O. alismoides can have an annual or perennial lifecycle depending on the climate, and reproduces only by seed. It has been introduced to Africa, Europe, and at least six U.S. states; established populations are present in Louisiana, Italy, Egypt, Iraq, Sudan, and possibly Tanzania. There is little information available on historical pathways of introduction, although hitchhiking on construction equipment, watercraft, waterfowl, and with rice seed have all been proposed as potential pathways. The species is rare but present in the global aquarium trade. O. alismoides is federally listed as a Noxious Weed, and is also regulated in at least nine U.S. states; there is concern that the species will negatively affect recreational activities, ecosystem functions, and rice production. However, the History of Invasiveness for O. alismoides is classified as Data Deficient because there is no information to determine the observed, actual impact from introduced and established populations. The climate matching analysis for the contiguous United States indicates establishment concern for this species. Climate match was highest along the Gulf and Southern Atlantic Coasts. The Certainty of Assessment is classified as Low due to lack of information on impacts caused by introductions. The Overall Risk Assessment Category for Ottelia alismoides in the contiguous United States is Uncertain.