Chinese hibiscus (Hibiscus rosa-sinensis L.) or tropical hibiscus is extensively planted as a flowering pot plant worldwide and as a flowering shrub throughout tropical regions. Hibiscus rosa-sinensis has not been reported from the wild and is generally a highly heterozygous polyploid of complex ancestry (Singh and Khoshoo, 1970). The Linnaean showy double red-flowered plant type was obtained from China where it was cultivated, although no wild forms of the species are known to exist there (Kimbrough, 1997). Indigenous hibiscus species from islands in the south Indian Ocean including H. schizopetalus Hook., H. liliiflorus Cav., H. fragilis DC., and H. boryanus Hook and Arn. in combination with the Pacific Island species H. kokio Hillebrand, H. arnottianus Gray, H. wimeae Heller, H. denisonii auct., and H. storckii Seeman are thought to have played a major role in the development of cultivated H. rosa-sinensis (Singh and Khoshoo, 1989).
Chinese hibiscus has moderately high pollen fertility (Singh and Khoshoo, 1989) but seed set is rarely observed under normal conditions in the tropics (Sharma and Sharma, 1962). Proper attention to environmental conditions during pollination was demonstrated to improve seed set in an Italian study with best set occurring in the spring and fall under moderate shade when the temperature ranged from 16 to 27 °C, and dew point was between 10 and 16 °C (Mercuri et al., 2009). Observations of seed set indicates some H. rosa-sinensis cultivars are superior female parents, whereas others are better male parents (Lawton, 2004).
Size, shape, and flower color as well as plant habit show great variation in Chinese hibiscus clones. Newer clones generally flower more freely in more diverse colors than heirloom clones and are cutting propagated instead of grafted (Dickey, 1950; Lawton, 2004). Modern breeding is generally directed at the hobby flower show, florist-grade flowering pot plant, or landscape shrub market segments. The hobby market is focused on floral traits with little attention to ease of propagation or plant morphology. Florist-grade clones are bred to be compact, responsive to growth regulators, have high bud counts under greenhouse production environments, and have dark green dense foliage. Breeding for the shrub market is limited by lower plant values and is generally serviced by screening clones developed for the other more financially lucrative market segments. Landscape shrub producers and consumers desire clones with characteristics such as rapid growth to fill bigger pots, environmental tolerance, and extended bloom cycles (Lawton, 2004). ‘USS Alabama’, ‘USS Mississippi’, ‘USS Missouri’, ‘USS Tennessee’, and ‘USS Texas’ were selected for the shrub market.
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