Weed Risk Assessment for Neptunia United States oleracea Lour. (Fabaceae) – Water Department of Agriculture mimosa Animal and Plant Health Inspection Service June 14, 2012 Version 1 Top left: Neptunia oleracea plants in flower; top right: Spongy, floating stem tissue of Neptunia oleracea; bottom: A colony of Neptunia oleracea plants (source: Technigro, 2011). Agency Contact: Plant Epidemiology and Risk Analysis Laboratory Center for Plant Health Science and Technology Plant Protection and Quarantine Animal and Plant Health Inspection Service United States Department of Agriculture 1730 Varsity Drive, Suite 300 Raleigh, NC 27606 Weed Risk Assessment for Neptunia oleracea Introduction Plant Protection and Quarantine (PPQ) regulates noxious weeds under the authority of the Plant Protection Act (7 U.S.C. § 7701-7786, 2000) and the Federal Seed Act (7 U.S.C. § 1581-1610, 1939). A noxious weed is “any plant or plant product that can directly or indirectly injure or cause damage to crops (including nursery stock or plant products), livestock, poultry, or other interests of agriculture, irrigation, navigation, the natural resources of the United States, the public health, or the environment” (7 U.S.C. § 7701-7786, 2000). We use weed risk assessment (WRA) —specifically, the PPQ WRA model1—to evaluate the risk potential of plants, including those newly detected in the United States, those proposed for import, and those emerging as weeds elsewhere in the world. Because our WRA model is geographically and climatically neutral, it can be used to evaluate the baseline invasive/weed potential of any plant species for the entire United States or any area within it. We use a climate matching tool in our WRAs to evaluate those areas of the United States that are suitable for the establishment of the plant. We also use a Monte Carlo simulation to evaluate the consequences of uncertainty on the outcome of the risk assessment. For more information on the PPQ WRA process, please refer to the document, Introduction to the PPQ Weed Risk Assessment Process, which is available upon request. Neptunia oleracea Lour. – Water mimosa Species Family: Fabaceae Information Initiation: On October 27, 2011, the Exotic Pest Information Collection and Analysis (EPICA) program reported that a population of Neptunia oleracea had been found in Arkansas in 2009, in the Little Maumelle River, along the Arkansas River flood plain (Peck and Serviss, 2011). This was the first detection of naturalized populations of N. oleracea in the United States. Joel Bard, the Arkansas State Plant Health Director, is concerned that stem fragments of N. oleracea could move downstream, allowing the plant to establish in more favorable, warmer areas of the United States. Foreign distribution: Neptunia oleracea is thought to be native to South America and introduced to other areas of the world (Bentham, 1875). Neptunia oleracea now occurs in Mexico and in over 50 countries in Central and South America, the Caribbean, Africa, and Asia (Windler, 1966). U.S. distribution and status: A colony of N. oleracea was detected in Arkansas in 2009 (Peck and Serviss, 2011). James Peck, professor of biology at Arkansas State University, says that a few stem fragments could still be found in 2011 (Peck and Serviss, 2011). Neptunia oleracea is available through the water garden and aquarium trade (Peck and Serviss, 2011; Ponds Plants and More, 2011; The Flowering Garden, 2011; The Water Garden, 2011Ponds Plants and More, 2011 #46}), so it may be present in other states in cultivation. WRA area: Entire United States, including territories 1 Koop, A., L. Fowler, L. Newton, and B. Caton. 2012. Development and validation of a weed screening tool for the United States. Biological Invasions 14(2):273-294. DOI:10.1007/s10530-011-0061-4 Ver 1. (Original) June 14, 2012 1 Weed Risk Assessment for Neptunia oleracea 1. Neptunia oleracea analysis Establishment/Spread Neptunia oleracea is a nitrogen-fixing aquatic plant (Yanasugondha and Buranakarl, Potential 1981) that roots on the edges of water bodies and then forms dense, floating mats of stems that spread rapidly over the water surface (Peck and Serviss, 2011; Windler, 1966). This plant is native to South America and has naturalized in over 50 countries in South and Central America, Africa, and Asia (Windler, 1966). Neptunia oleracea is propagated by seeds and stem fragments that are dispersed by water (Australian Weeds Committee, 2011; Technigro, 2011), therefore mutilation facilitates the spread of this species. People can spread seeds in mud attached to machinery and vehicles (Technigro, 2011). This risk element had average (moderate) uncertainty because we could not answer questions about the number of seeds produced, minimum generative time, and if N. oleracea can form seed banks. Risk score = 14 Uncertainty index = 0.18 Impact Potential Neptunia oleracea produces dense, floating mats that can replace native wetland plants, block water flow in creeks and drains, restrict boat access, reduce water quality, and kill native plants and fish (Australian Weeds Committee, 2011; Queensland Government, 2009). Neptunia oleracea is listed as a Class 1 Pest Plant (introduction into the state is prohibited, and landowners must take reasonable steps to keep land free of this species) in Queensland, Australia (Queensland Government, 2009), where it is controlled in natural ecosystems through mechanical and chemical controls (Technigro, 2011). In urban/suburban environments, it restricts boat access, blocks drains, and creates a favorable habitat for certain species of mosquitoes (Queensland Government, 2009). Neptunia oleracea has also been reported as a weed of rice fields in southeast Asia (IRRI, 1993; Moody, 1989). This risk element had an average amount of uncertainty. Risk score = 3.1 Uncertainty index = 0.12 Geographic Potential Neptunia oleracea is an aquatic plant that grows in wetlands, bodies of fresh water, and slow-running tropical rivers (Bentham, 1875; Windler, 1966). To evaluate its potential distribution in the United States, we had to determine if it could survive the winters where it was found in the Little Maumelle River in Arkansas, a region in USDA Plant Hardiness Zone 8. We consulted with Dr. Brett Serviss, a plant biologist at Henderson State University who co-authored the paper reporting the Arkansas colony of N. oleracea. Dr. Serviss thought that N. oleracea might be able to overwinter in Arkansas during warm winters if the water did not freeze, but he did not think that the N. oleracea colony would be able to expand and spread in Arkansas (Serviss, 2011). However, Dr. James Peck, the biology professor from Arkansas State University who found the Arkansas colony, reported that a few stem fragments of the original Arkansas colony remain, suggesting that, at least for the last few years, it has been able to survive cold winter temperatures (Peck, 2011). He reports that stem fragments seem to sink into the water in the fall, thus avoiding the freezing ice. It is also possible, however, that the population has survived only because it is recolonized by people growing the plant as a vegetable. In our analysis, we assumed that N. oleracea can survive in Plant Hardiness Zone 8. We estimate that about 20 percent of the United States is suitable for the establishment of N. oleracea (Fig. 1). The predicted distribution is based on the species’ known distribution elsewhere in the world and includes point-referenced localities and areas of occurrence (GBIF, 2011). The map for Neptunia oleracea Ver 1. (Original) June 14, 2012 2 Weed Risk Assessment for Neptunia oleracea includes the joint distribution of USDA Plant Hardiness Zones 8-13, areas with 0- 100+ inches of annual precipitation, and the following Köppen-Geiger climate classes: tropical rainforest, tropical savanna, steppe, desert, humid subtropical, and marine west coast. Entry Potential We did not assess entry potential because N. oleracea has already naturalized in Arkansas (Peck and Serviss, 2011) and is cultivated in U.S. aquariums and water gardens (The Water Garden, 2011; The Flowering Garden, 2011; Ponds Plants and More, 2011). Figure 1. Predicted distribution of Neptunia oleracea in the United States. Map insets for Alaska, Hawaii, and Puerto Rico are not to scale. Ver 1. (Original) June 14, 2012 3 Weed Risk Assessment for Neptunia oleracea 2. Results and Conclusion Model Probabilities: P(Major Invader) = 73.7% P(Minor Invader) = 25.3% P(Non-Invader) = 1.1% Risk Result = High Risk Secondary Screening = Not applicable Figure 2. Neptunia oleracea risk score (black box) relative to the risk scores of species used to develop and validate the WRA model (other symbols). See Appendix A for the complete assessment. Figure 3. Monte Carlo simulation results (N=5000) for uncertainty around Neptunia oleracea’s risk scoresa. a The blue “+” symbol represents the medians of the simulated outcomes. The smallest box contains 50 percent of the outcomes, the second 95 percent, and the largest 99 percent. Ver 1. (Original) June 14, 2012 4 Weed Risk Assessment for Neptunia oleracea 3. Discussion The result of the WRA for N. oleracea is High Risk. Neptunia oleracea is a floating aquatic plant that spreads quickly over the surface of fresh bodies of water and replaces native wetland plants, blocks water flow in creeks and drains, restricts boat access, and reduces water quality (Queensland Government, 2009). Comparison of N. oleracea to the 204 species used in the validation study indicates that it shares many of the same traits and impacts as other major- and high-scoring minor-invaders (Fig. 2). In the uncertainty analysis, the simulated risk scores all resulted in a conclusion of High Risk (Fig. 3), indicating that the overall model conclusion is highly robust. In this WRA, we considered Plant Hardiness Zones 8 and above as suitable for the establishment of Neptunia oleracea. If only Zones 9 and higher are suitable for this species, then we estimate that approximately 6 percent (versus 20 percent) of the United States is suitable for this species.