Trailing lantana [Lantana montevidensis (Spreng.) Briq.] is a low-growing, woody shrub or sprawling groundcover native to tropical areas of South America. The leaves are simple, opposite, rugose, ovate in shape, with dentate margins and a pungent odor when crushed. The attractive umbel inflorescences are typically lavender in color with varying degrees of white and/or yellow in the center of corolla tubes. Flowers are followed by an infructescence of ellipsoid drupes turning from green to purple when ripe (Dehgan, 1998).
As early as 1825, the species was described by the German botanist Curt Polycarp Joachim Sprengel (Johnson, 2007, 2009). It has since escaped cultivation and is considered invasive in many subtropical ecosystems from Hawaii, Australia, and the Southeast United States. The invasiveness of trailing lantana is attributed to several factors, including 1) its ability to produce large amounts of fruit that are dispersed by birds, 2) the presence of an underground storage organ (xylopodium) facilitating its resilience to fire, drought, and herbicide, 3) its potential to produce two embryos per seed (apomixis) that germinate under a range of conditions, and 4) its ability to spread vegetatively (O’Donnell, 2002). Due to its rapid expansion and colonization of native lands and improved pastures in Australia, trailing lantana is a restricted invasive prohibited for use by the Queensland Biosecurity Act of 2014 (Johnson, 2007, 2009; 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), 2020]. In Florida, herbarium vouchers have documented its escape in 18 counties (Wunderlin et al., 2020).
To date, trailing lantana has not been listed as a Category I or II invasive plant by Florida’s Exotic Pest Plant Council (FLEPPC, 2019). However, based on a predictive test, the University of Florida/Institute of Food and Agricultural Sciences’ (UF/IFAS) Assessment of Non-Native Plants in Florida’s Natural Areas does not recommend its use in northern, central, or south Florida, because it has a high invasion risk (UF/IFAS Assessment, 2020a). The predictive tool used to make this conclusion is a weed risk assessment protocol consisting of 49 questions that address the history of the species, along with its biogeography, life history traits, and ecology (Lieurance et al., 2016). Each question receives a numerical score between −3 and 5 points, and conclusions are made based on the cumulative score. Any score greater than 6 means a high risk of invasion. Trailing lantana received a score of 29 and is therefore not recommended for use in Florida (UF/IFAS Assessment, 2020b). Specifically, the species scored a value greater than 0 for 25 of the 49 questions, with heavier weighted scoring designated due to it being a weed of agriculture (4 points), a weed of environmental harm (4 points), a garden weed (2 points), a congeneric weed sharing the genus of the highly invasive Lantana camara L. (2 points), and the documented naturalization beyond its native range (2 points). In Florida, all cultivars fall under this classification unless proven otherwise through an internally approved UF/IFAS Infraspecific Taxon Protocol (ITP) evaluation. This protocol consists of 12 questions to determine 1) if the taxon displays invasive traits that cause greater ecological impact than the wild type or resident species and if it can be readily distinguished; and 2) the fecundity of the taxon and its chances of regression or hybridization to characteristics of the resident/wild type species (Lieurance et al., 2016).
Interestingly, in Australia two forms of trailing lantana have been reported that differ in their ability to produce fruit (Johnson, 2007, 2009). Steppe et al. (2019) obtained a permit to import germplasm from the fruiting Australian form into the United States. They also collected different U.S. forms sold from various nurseries in Florida and a naturalized form from Texas. A total of eight different varieties of trailing lantana were evaluated for morphological and cytological distinctions. It was discovered that Australian trailing lantana differed morphologically and cytologically from the U.S. varieties (Steppe et al., 2019). Most noticeably, leaves of Australian trailing lantana were smaller with fewer leaf serrations, distinct serrate-crenate margins, and less appressed hairs. Also, well-developed, stainable pollen grains were observed in the anther sacs of the Australian trailing lantana but absent in U.S. varieties. Finally, the Australian trailing lantana was determined to be a tetraploid, but all U.S. varieties evaluated were triploids. The current study was conducted to explore the landscape performance, flowering, and female fertility of these eight trailing lantana varieties planted in replicated field trials at two locations in Florida.
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