Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 8/31/2009
Publication Date: 1/31/2012
Citation: Hoch, P.C., Grewell, B.J. 2012. Ludwigia. Book Chapter. In: Baldwin, B.G. (convening ed.) The Jepson Manual, Vascular Plants of California, 2nd edition. Berkeley, CA: University of California Press. p. 948-951. Interpretive Summary: Ludwigia species have become aggressive aquatic weeds in California, while former taxonomic treatments for identification are inaccurate and out of date. The Jepson Manual has become the authoritative floristic reference for the state of California, and is used by professional botanists, agency personnel, environmental consultants, conservation planners, teachers, and students as a conservation tool and a primary resource for plant identification. The 1st edition of the Jepson Manual (published 16 years ago), rapidly became out-of-date as a result of the phenomenal progress in plant systematics. This substantially revised taxonomic treatment of the Ludwigia genus is a contribution to the forthcoming 2nd edition of the Jepson Manual. The treatment is based on extensive biosystematic research of Ludwigia populations throughout California. L. hexapetala and L. peploides taxa previously thought to be native to California are now recognized as naturalized and disjunct from their native South American range. A recently introduced and naturalized invasive species, L. grandiflora, is now included.
Technical Abstract: The Jepson Manual; Higher Plants of California is the authoritative floristic reference for the state, that has rapidly become out of date given substantial advances in plant systematics and the arrival of new exotic species. Recent aggressive spread of Ludwigia species (Onagraceae) has impacted sensitive wetlands, water conveyance canals, and rice fields in Pacific western states. Variable growth responses to environmental conditions and contradictory taxonomic keys have complicated accurate species identifications that are essential for weed management. Here we present a revised taxomomic treatment for Ludwigia (Onagraceae) found in California. The updated taxonomic descriptions and key are based on extensive biosystematics research, and considers currently available cytological, morphometric and molecular data. The treatment describes six Ludwigia taxa in California, while previously only five were recognized. The treatment now includes the recently introduced invasive weed, L. grandiflora. L. hexapetala and L. peploides taxa previously thought to be native to California are now recognized as naturalized and disjunct from their native South American range.