Ruellia L. consists of ≈250 species of perennial herbs, subshrubs, and shrubs with mostly tropical and subtropical distribution and is one of the largest genera in the Acanthaceae (Ezcurra, 1983). Ruellia simplex Wright (commonly known as mexican petunia, mexican bluebell, or Britton’s petunia) has low maintenance requirements and prolific flowering and has become a very popular landscape plant in the southern United States (Gilman, 1999) since its introduction to Florida sometime before 1940 (Hupp et al., 2009). There are many synonyms for R. simplex (R. brittoniana Leonard, R. coerulea Morong, R. malacosperma Greenm., and R. tweediana Griseb.) with the name R. simplex being the first documented, thus having taxonomic priority (Ezcurra and Daniel, 2007). A meiotic complement of n = 17 appears to be widespread in Ruellia (Daniel et al., 1984). Ruellia simplex (as R. tweediana) has also been reported as 2n = 34 (Piovano and Bernadello, 1991).
Ruellia simplex has naturalized in disturbed uplands and wetlands of six southern U.S. states (from South Carolina west to Texas) plus the U.S. Virgin Islands, Puerto Rico, and Hawaii (Kartesz, 2012; U.S. Department of Agriculture, Natural Resources Conservation Service, 2012). Since 2001, the Florida Exotic Pest Plant Council has considered mexican petunia as a Category I invasive plant, described as “plants that are altering native plant communities by displacing native species, changing community structures or ecological functions, or hybridizing with natives” (Florida Exotic Pest Plant Council, 2011). The Institute for Food and Agricultural Science (IFAS) Assessment of the Status of Non-Native Plants in Florida’s Natural Areas does not recommend use of mexican petunia in the central and southern parts of Florida, and in northern Florida, its specified use needs to be approved (IFAS, 2011).
Currently there are tall (‘Purple Showers’, ‘Chi Chi’, and ‘Snow White’) and dwarf (‘Katie’ and ‘Southern Star’ series) cultivars available of R. simplex in purple, pink, and white flower colors. These cultivars are clonally propagated, except for the ‘Southern Star’ series, which is propagated by seed (PanAmerican Seed Co., Chicago, IL). With the exception of ‘Purple Showers’, which does not set fruit by open pollination (Wilson and Mecca, 2003), all known cultivars set fruit and are potentially invasive. Sales of ‘Purple Showers’ in Florida were ranked third for herbaceous perennials after pentas and lantana (Ornamental Outlook, 2009). A survey conducted in 2002 including 946 active nurseries in Florida indicated that 15.9% of them grew or sold R. simplex, and total reported annual sales for this plant was estimated at ≈$12 million (Wirth et al., 2004).
Since 2007, we have developed the first Ruellia breeding program at the University of Florida (UF)/IFAS in Gainesville, FL, directed specifically toward creating new sterile cultivars for the landscape plant industry. To reduce the spread of R. simplex by seed, female sterility (and fruitlessness) or lack of seed viability is desired. The breeding lines of Ruellia described below were obtained by a combination of polyploidization using oryzalin and hybridization. They were selected in multilocation trials in Florida from a group of 15 different clones for superior landscape performance as compared with commercial cultivars and no fruiting (Freyre et al., 2012).
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