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Trailing lantana (Lantana montevidensis) is a popular low-growing ornamental plant valued for its heat and drought tolerance and continuous purple or white flowering throughoutmuch of the year. Recently, trailing lantana was predicted to be invasive by the University of Florida/Institute of Food andAgricultural Sciences (UF-IFAS) Assessment of Non-Native Plants in Florida, and therefore not recommended for use. All cultivars fall under this designation unless proven otherwise. Eight trailing lantana varieties were obtained from wholesale growers and naturalized populations found in Texas and Australia. Plants were propagated vegetatively, finished in 4-inch pots, and planted under field conditions to determine morphological and cytological differences among varieties. Australian trailing lantana differed morphologically from the other varieties in its smaller habit, leaves (which had serrate-crenate leaf margins, and fewer appressed hairs), heavy fruiting, and cold sensitivity (observational reduced growth and flowering during winter months). Nuclear DNA content analysis suggests that Australian trailing lantana is likely a tetraploid and all other varieties evaluated were likely triploids with high levels of sterility. Pollen stainability of Australian trailing lantana was moderately high (58.83%), whereas pollen production was rarely observed in all other varieties. Results support that there are two forms of trailing lantana, the U.S. varieties distinguished by their leaf and flower morphology, ploidy level, and the absence of fruit and viable pollen. Trailing lantana (Lantana montevidensis) is a low-growing woody shrub native to tropical areas of South America. As early as 1825, the species was described by German botanist Curt Polycarp Joachim Sprengel as Lippia montevidensis. This plant has also been described as Lippia sellowiana or Lantana sellowiana to honor German botanist Friedrich Sellow (or Sello). Finally, in 1904, it was reclassified as Lantana montevidensis by the Swiss botanist John Isaac Briquet and this name remains today (International Plant Names Index, 2015). The genus refers to the original Latin name for Viburnum ‘‘Viburnum lantana,’’ having a similar inflorescence structure. The specific epithet is derived from Montevideo, Uruguay, where the plant was first found (Johnson, 2007). Trailing lantana is listed as an invasive exotic in many subtropical ecosystems from Hawaii and Australia to the southeastern United States. In Australia, due to its rapid expansion and colonization of natural lands and improved pastures, trailing lantana is a restricted invasive prohibited for use by the Queensland Biosecurity Act of 2014 (Day et al., 2003; Johnson, 2007; Munir, 1996; O’Donnell, 2002). In the United States, it has escaped cultivation in seven states, including Alabama, California, Florida, Georgia, Hawaii, Louisiana, and Texas [U.S. Department of Agriculture, National Resources Conservation Service (USDA, NRCS), 2019]. In Florida, herbarium vouchers document its escape in 18 counties (Wunderlin et al., 2019). To date, trailing lantana has not been listed as a Category I or II invasive plant by the Florida Exotic Pest Plant Council (FLEPPC, 2019). However, based on a predictive test, the UF/IFAS Assessment of Non-Native Plants in Florida’sNatural Areas does not recommend its use in northern, central, or southern Florida, with results concluding that it has high invasion risk (UF/IFAS Assessment, 2019). All cultivars fall under this conclusion unless proven otherwise and exempted from the ruling. Trailing lantana is characterized by having a horizontal growth habit, with branches rooting at the nodes. Leaves are opposite, broadly ovate, and strongly aromatic when crushed. Umbel inflorescences, each containing 30 florets, are borne on long axillary peduncles 30 mm in length. If present, blackberry-like fruit is drupe, each having one seed and up to two embryos. In Australia, Johnson (2007) reported two forms (cultivated and wild) of trailing lantana differing in their ability to produce fruit. The Australian weedy variety was described as having purple flowers with white throats, and the ornamental nonweedy variety (cultivated garden form) was described as having either lilac petals with white to yellow throats, or white petals with yellow throats. Although the lavender variety is more popular in the trade, there is a white-flowered form L. montevidensis forma albiflora that was collected from the wild in Brazil as early as 1944 (IPNI, 2015; San Marcos Growers, 2019). Similar to the lavender variety, the white form flowers year-round and is drought tolerant and adapted to full sun or part shade in USDA cold hardiness zones 8 to 10 (USDA, 2012). Henderson (1969) reported that the two forms of trailing lantana in Australia also differed dramatically in pollen viability and ploidy level/chromosome number. The weedy form had 65% pollen stainability and was a tetraploid with 2n = 4x = 48 chromosomes, whereas the garden form had extremely low pollen stainability (less than 6%) and was a triploid with 2n = 3x = 36 chromosomes. In India, only the triploid trailing lantana was noticed (Raghavan and Arora, 1960). Although the introduction of new trailing lantana varieties is insignificant compared with L. camara, there has been some selection of the species with named patents (Google Patents, 2019). In 1990, Monrovia Nursery introduced White Lightnin trailing lantana (L. montevidensis ‘Monma’) and Lavender Swirl trailing lantana (L. montevidensis ‘Monswee’) that are still popular today. In 2007, Proven Winners released Received for publication 1 Aug. 2019. Accepted for publication 11 Sept. 2019. We gratefully acknowledge funding support from the U.S. Department of Agriculture’s (USDA) AgriculturalMarketing Service and FloridaDepartment of Agriculture and Consumer Services Specialty Crop Block Grant Program, Florida Fish and Wildlife Conservation Commission, and Florida Nursery and Growers and Landscape Association. The contents of this publication are solely the responsibility of the authors and do not necessarily reflect the official view of the USDA. We thank Mark Kann, Chris Harchick, Bart Schutzman, Krishna Bhattarai, Julia Rycyna, and Jackson Jablonski for technical assistance; and Megan Thomas and Adam Black for plant collection assistance. This paper is based on a presentation given during the Annual Meeting of the Florida State Horticultural Society, which was held 9–11 June 2018, in Orlando, FL. C.S. is the corresponding author. E-mail: csteppe@ ufl.edu. 2134 HORTSCIENCE VOL. 54(12) DECEMBER 2019 Luscious grape trailing lantana (L. montevidensis ‘Robpwpur’) and it has since received prestigious awards as a top performer from plant trials at Kansas State University, University of Georgia, Texas A&M University, Longwood Gardens, North Carolina State University, and University of Delaware. In 2013, Lord Brooks trailing lantana (L. montevidensis ‘Lord Brooks’) was patented as a new variety distinguished by its darkercolored purple flowers. Unnamed white and lavender trailing varieties are also commonly available from nurseries throughout the United States. To our knowledge, all U.S. varieties are propagated vegetatively, as fruit is extremely rare or absent altogether. Among the known trailing lantana introductions in the United States, none have been reported from planned breeding programs for plant morphology, female sterility, pollen stainability, and/or ploidy level, such as with Lantana camara (Czarnecki et al., 2012; Deng et al., 2017). The objective of this study was to assess morphological and cytological differences among eight trailing lantana varieties collected from different growers and a naturalized area in Texas and Australia. Information in these aspects was much needed to determine the invasive potential and suitability for continued commercial production and landscape use in the United States. Materials and Methods Plant material. Eight sources of trailing lantana were identified for use in this study, as described in Table 1. Four of the plant Table 1. Varieties of trailing lantana (Lantana montevidensis) evaluated for morphological and cytological comparisons. The source of plant material and contact information are shown. Source/variety Contact/company Additional information provided if available American Farms (AF) lavender trailing lantana Justin Orion, American Farms, Naples, FL Unrooted cuttings produced from Dummen’s ORO farm in Guatemala Australia (AUS) trailing lantana Megan Thomas, Queensland Herbarium, Brisbane Botanic Gardens Naturalized location in Queensland Australia, Permit USDA APHIS P37-17-01621 Costa Farms (CF) lavender trailing lantana Purchased through distributer, Lowe’s, Gainesville, FL Costa Farms, Miami, FL Hatchett Creek Farms lavender trailing lantana (HCTL) George Griffith, Hatchett Creek Nurseries, Gainesville, FL Mother plants obtained 20+ years ago Hatchett Creek Farms white trailing lantana (HCTW) George Griffith, Hatchett Creek Farms, Gainesville, FL Mother plants obtained 20+ years ago Luscious grape trailing lantana Jim Putman, New Products Manager, Proven Winners (PW) ‘Robpwpur’ is a product of a planned breeding program developed by plant breeder, Robert J. Roberson. It was discovered in July 2002 as a naturally occurring branch mutation of Lantana montevidensis ‘Alba’. Base of leaf blade is cuneate rather than cordate (trailing purple). Has denser pubescence on lower side of the leaf blade and darker violet main color on the upper side of the flower. Application date: 2007 (Google Patents, 2019) Riverview Farms (RF) purple trailing lantana Rick Brown, Riverview Farms, Seffner, FL Quality Cuttings, Mexico

Morphological and Cytological Comparisons of Eight Varieties of Trailing Lantana (Lantana montevidensis) Grown in Florida